'06 9-7X 5.3i :: Intermittent Voltage Surge While Driving

[MTBoss]

Greetings all,

TL;DR - 2006 Saab 9-7x 5.3i has intermittent voltage spikes while driving at a range of ~1500-2500 RPM which causes the vehicle to "jerk" or "jolt" as if power to the engine was momentarily lost for half a second along with a CEL popping in for a second and clearing. This happens randomly, from back to back within a mile of driving, to once over the span of 20 miles, at anywhere from 35mph to 80mph. Battery, Alternator, and Spark Plugs were replaced. Tech 2 shows clean misfire logs. System voltage stays at ~ 14.4V while engine is running, and spikes are hitting ~16V per Torque logs. Intermittent nature of the issue, and the fact that it only seems to happen while driving (haven't seen it at idle yet) leads me to believe it could be ground related. No stored/pending CEL codes. Looking for suggestions on what to check.

Essay version for details:

I've got a seemingly odd issue with my 2006 9-7X that I'm hoping to get some suggestions on. This vehicle isn't a DD and I mostly use it for fishing trips, kayak hauling, and light towing, so I'm not in a situation where I need to take it into a shop for a quick fix. I enjoy problem solving, so I've been "learning" bits and pieces of automotive repair with this vehicle.

All of that being said, I can't seem to find any information on the issue I'm experiencing, so I decided to finally make a post and see what comes of it. Here's a bit of the background on what happened with the vehicle, what I've replaced so far, and where it stands today:

About a year back the vehicle had been sitting a while with a drained battery, and as the vehicle was being jumped and voltage was returning to the battery, the electrical system starting flaking out. The alarm went off and some previously unknown headlight washer fluid apparatus extended from the front bumper and began spraying water into the air. I didn't know those were even in the vehicle, as I don't have headlight wipers, so that was somewhat of a shock. Nevertheless, the battery charged and I was able to start the vehicle. After idling for about 5 minutes, the engine just turned off on its own, but all of the electrical components were still on, the dash was illuminated, radio was on, etc., and I got a Stabilitrak Off message across the dash. After that happened it wouldn't crank over immediately, and took about a minute or so before it would start up again. Thought it was maybe a fluke, but it ended up happening again, so I started looking into the issue.

I kept running the vehicle idle to see if it would throw a code, and eventually it spit out a p0601: Internal Control Module Memory Check Sum Error. After checking some forums, it seemed my PCM was corrupted. Not having access or insight into the world of PCM programming, I wasn't really sure if the issue was purely logical and could have been corrected with a retune or reloading on firmware, so I ended up buying a used replacement from the same year/make/model/trim off of ebay. They said they were going to push my VIN on the replacement PCM as well, but they actually never did that, so I currently have a mismatched VIN, although I'm not sure if any other component in the vehicle have the VIN encoded.

After swapping the PCM, I ended up buying a clone "Tech 2" off of Alibaba to perform the Crankshaft Position Sensor Relearn, and got the vehicle running again. All was good for a while, but while driving we started noticing the AC would randomly stop blowing cold. If we turned the AC button off and on again it would come back. After a while, I'd see a check engine light flash and the vehicle would feel like it lost power for a split second and jerk or jolt. And then the AC compressor would be off, so it seemed like the two issues were intertwined. At some point, the AC quit blowing cold altogether, and the Tech2 showed a Low Pressure status. R134 levels seemed fine, so assuming it's a low-pressure switch (which I haven't replaced yet,) but I've been running the vehicle without the AC system engaged at all and it would still have the random loss of power.

The power loss issue that feels like the vehicle jolts or jerks for a split second seems to be fairly random. I've had it happen while driving around town at ~35mph, and on the highway up to 80mph. It seems to be within the 1500-2500 RPM range, but that's where most of my driving occurs, so that doesn't really explain much. I haven't seen it hit while idling yet, so the vehicle being in motion could be a factor (maybe something with the yaw rate sensor?) The time between it jerking is also random. Sometimes it'll happen back to back within a minute, and other times I've driven 20 miles between events. I don't drive the vehicle regularly, but have a nice 35 mile commute to work that I've been taking it on to try and collect data. Probably not the safest choice considering the symptoms, but I haven't had a great way to test it otherwise.

Anyhow, ended up downloading Torque and used a WiFi OBD scanner to try to isolate what was happening to the vehicle when it would jerk or jolt. It seemed like it was having a voltage drop, but Torque actually showed the system voltage was spiking up to nearly 16V. Thought this could have been the alternator, so I replaced it, but it still did the same thing afterwards. Tried to find some info on a Voltage Regulator, but it seems it's built into the alternator, so I don't think the issue would have persisted after changing. Since this started, I've replaced the battery, alternator, and just recently did the plugs using AC Delco 41-110 Iridiums. I did have some really bad Misfires on 4 before the plug change, and it has since cleared up.

At this point I'm not entirely sure what to check next. I checked the fuse panel wires at both panels for short to ground, and didn't find anything suspect. Seems like it could be related to a bad ground somewhere, but all of the easy/accessible grounds have been cleaned, tightened and checked for voltage drop. I've got the clone Tech2 available, and I'm willing to setup an XP machine with TIS2000 if anyone thinks there's something worthwhile to check along that route.

If you read all of this, I appreciate it. This forum has been an awesome resource throughout the years, so I'm hoping some of you folks can point me in the right direction.

Regards.

 

[Mooseman]

Hi and welcome!

Not to sure what to make of the voltage spikes and drops. Did you recheck all your battery connections and grounds? I think you also have a SARVC voltage regulator on the negative battery cable. It regulates how much the alternator works according to power demands to help extend battery life. If you disconnect it, the alternator will work like an older one always keeping voltage at 14V.

Maybe someone else has some ideas.

 

[Reprise]

Like Mooseman mentioned, check to see if you have a SARVC, and disable it. Do this first, as it's the cheapest / easiest solution. You may be able to test it with the Tech2 - ?

If it's 'ok at idle', like you mentioned, you may need to set up a data capture while you recreate the drive cycles to trigger it.

GM's part # for it is 25826405 , Generator Battery Control Module. It's discontinued, but you can still find a new one in various places for about $100. I'd probably source a used one (junkyard) if you want to replace it. But if merely disconnecting it resolves the issue, I think I'd leave it like that for a bit, myself.

Saab also uses that number, along with 25816746 (superseded).

Chevy and GMC used it (all MY, all engines), along with most of the other 360s, and a couple of other platforms, too (Colorado, Canyon, Hummer H3, H3T). It's the same part, so no need to source it from a Saab parts resource.


Another thought... you could have someone like Jeremy ( @limequat) take a look at the PCM, when you order up a tune from him (he charges only $99 for the GMT360s, so probably the cheapest resource you could secure to do this). He'll also do a regular tune for you, of course, as long as nothing's wrong with the ECM.

If you still have the old original ECM, chat with Jeremy about whether it can be reflashed. If it can, that might be the better one to send him. Or, he can let you know if it can be recovered with the TIS2000, in which case, you can prep up a laptop and have at it.

I saw you put in new iridium plugs. Did you put new wires in, or test the resistance? Same for the coils. Especially start with #4, since you were having issues with that plug. But I doubt a coil / plug wire is doing this, TBH.

I know that's kinda taking the parts shotgun to it, but it's the best I can think of for now. As I wrote this post, I started thinking more and more along the lines of the battery ctrl module getting fried along with the ECM, when you jumped it (when you think about it, it's right inline in the electrical path, right?) So that's where I'd start.

 

[MTBoss]

@Mooseman @Reprise

Really appreciate the quick feedback fellas! I’ll see about removing the SARVC and report back.

Concerning the data capture, is there anything in particular you think would be good to focus on? Not sure if the phone apps like Torque or OBD Fusion would produce logs suitable to diagnose a problem? One caveat with the Tech 2 that I failed to mention is that when this issue occurs I lose connectivity with the Tech 2 Via OBD, so any logs get disrupted. Don’t seem to have the same issue with the WiFi OBD module though.

Resistance was good across all of the plug wires, surprisingly, even though #2 and #8 got yanked pretty good after about 15 minutes of trying to avoid breaking the wires. I’ll keep the coils & plug wires in mind if nothing else seems to pan out. Agree it doesn’t seem likely that would cause this issue, but I have heard horror stories of bad coil packs hiding electrical gremlins, so who knows.

Thanks for tip with Jeremy; I’ll have to reach out and see about checking that other ECM. That’s a steal for a tune!

 

[Reprise]

He turns 'em around quick, too. (no problem for you, since this isn't a DD). He's seen this post, so I expect he'll be looking for a PM / e-mail from you, soon.

*After* looking at the battery module, don't forget

The Tech2 is very sensitive to voltage interruption, more so than the Torque / BT apps.
Moose has a post on how to get around the voltage issue on the Tech2 - search on his posts to find it. It may help you.

BUT -- if you set up a capture on the Tech2, it *should* write to memory, until such point as the voltage gets interrupted? WAG on my part, but it's worth trying. It may write to volatile (chipset) memory until the capture is stopped; if that's the case, you'll probably lose the capture. But if it transfers to non-volatile / card memory once the buffer fills, or the TIS2000 (connected in-line) can capture / save it in real-time, then you'd be OK.

Unfortunately, I'm not an expert on Tech2, even though I have one, myself
(I got old and stopped caring about trying to learn 'everything about everything'...lol)

I'd think you'd want to set up data logging on the secondary ignition / electrical system. Run a test (non-logging) on the Body Control Module, as well, to eliminate that as an issue.

 

[limequat]

Generally any of the P060x codes is lights-out for a PCM. It doesn't happen often, but when it does, I recommend scrapping them.

That said, it wouldn't hurt to try rewriting it with the Tech II clone in this case.

The replacement PCM should be fine. Using a module from a same make/model/year donor without updating the VIN is the same process I use for my loaners.

I wonder if there isn't a ground issue to the PCM specifically. The PCM has one dedicated ground. Interrupting ground prevents the module from doing a proper shut down, and could have even caused the original P0601. Also I wonder if the SARVC defaults to 16 volts when there is no serial message from the PCM.

You could try wiggling the engine wiring harness to induce the fault. Monitoring voltages won't detect this issue, but maybe there's a way to monitor module current?

 

[budwich]

the easiest test of the SAVRC control "system" is to just disconnect the plug going to it. This causes the system to run like a "normal old time alternator" putting out somewhere in the 13.8 volts range ALL the time. You can drive it like that for a while and see if your "overvoltage" issue shows up. Go from there depending on the results.

 

[MTBoss]

@Reprise thanks for the tip on the Tech 2, I’ll check out the post.

It seems my vehicle doesn’t have an SAVRC after all. The battery cables look stock as well, so I don’t believe it was replaced by the previous owner (bought this in 2014 with 75k miles on it.)

I think I’ll take another pass at checking all of the grounds; I only hit the easily accessible lugs when I last checked. And I’ll try putting some wiggle onto the wiring harness to see if it inducing the issue as @limequat suggested. And I’ll be in touch on the PCM tune for the replacement unit that’s currently installed.

Lots of good suggestions; I may try to take a pass at some of it this afternoon, but I’ll be out of town for work until Friday, so I likely won’t get into it until next weekend.

That being said, I’m starting to wonder about a potential Body Control Module issue as well. Does that unit control the theft system/alarm? Wondering if the issue that started when jumping the battery impacted something with the BCM, or wiring/grounds to the unit, since the alarm was going haywire during jump. I also discovered an issue I hadn’t previously seen that’s somewhat linked to the jumping battery event: the rear wiper fluid pump blows the 20A fuse (7 - WPR) when activated, and this pump also seems to connect to those previously unknown headlight wiper fluid reservoirs that randomly started discharging fluid during the jumping event as well. Maybe there’s a connection?

Thanks again all, will report back when I make some progress.

 

[limequat]

@MTBoss , pretty sure the theft system is its own module.
I thought of a few more connections to support my hypothesis. The A/C button is a momentary contact. If the PCM were to reset, it would go back to it's normally-off state. Also it would make sense that you wouldn't be able to talk to the PCM via OBD during the issue, as it would be off!
Finally, you mentioned sometimes the check engine light would come on during the issue. There's only two times the CEL comes on: 1) there is a fault stored, 2) the PCM is running bulb check. #2 only happens after -you guessed it- a reset.

 

[Mooseman]

I also discovered an issue I hadn’t previously seen that’s somewhat linked to the jumping battery event: the rear wiper fluid pump blows the 20A fuse (7 - WPR) when activated, and this pump also seems to connect to those previously unknown headlight wiper fluid reservoirs that randomly started discharging fluid during the jumping event as well. Maybe there’s a connection?

This is one the Saab's oddities. The headlamp washers don't have their own button compared to other GMT360's. It is activated only by the BCM every four times the windshield washer is used. Very annoying and useless waste of washer fluid. I pulled the relay for it. As far as your rear pump is concerned, it could just be internally shorted or the wiring to the pump is shorted. Testing would be required.

 

[MTBoss]

Ended up getting delayed and didn’t get a chance to work on the Saab until today. I went through the grounds again, moved just about every wire/wiring harness while the vehicle was running, and dismantled the main fuse block to check for breaks. Still wasn’t able to trigger the issue in park/idling. I did end up adding a 6AWG ground from the alternator mounting chassis to the frame ground that is closest to the battery negative terminal. I had the wire from a work project and just thought I’d throw some lugs on it to see if it improved anything. Probably should have waited til after doing the tests with the wiring before doing that.

Anyhow, got it all back together and haven’t taken it on the road yet; may try a drive cycle later in the week.

I did find a short clip I made a while back of the dash to try to identify what the gauges were doing while the issue happened. It’s crappy quality, but I turned it into a gif for easy viewing:



Quality is rough because I was just trying to point my phone at the dash while driving in hopes of capturing it. One thing I noticed here is the speedometer and tachometer dropping so immediately. The tach makes sense if the engine actually stalled for a fraction of a second, but the speedometer? Other gauges didn’t seem to be affected except the battery gauge, which seems to start crawling upward right after the event takes place. It’s sort of lost in the gif, but you can see it if you want a few times.

If anyone has any new ideas on what to check in light of that clip please let me know. Will update after I drive it a bit to see if the added ground has any impact.

 

[MTBoss]

Morning folks.

Had an interesting commute this AM. Took the Saab to get a drive cycle in and had a really minor blip about 7 miles into the commute, less of a jerking than usual, and then it seemed to be driving smooth for another 20 miles or so. Then I had the voltage spike, Stabilitrack Off flashes on my dash, and the entire dash died, including all interior lights, climate control, and radio. Had OBD Fusion running (similar to TORQUE but for iOS) and see the battery voltage and control module voltage spikes up to 16-17V.

Slowed down to a stop and everything came back on, and all of the voltage values returned to normal. As soon as the RPMs ramp up from idle, the voltage spikes again and the dash cut out. Probably not the safest decision, but I couldn’t exit and wasn’t far from work, so I kept driving the vehicle. Voltage was actually at the highest levels with lower speed but moderate RPM, so it was actually a bit better to just resume 60-70 MPH. At some point the dash would start to flicker back on and then I got a “battery not charging” prompt.

Interestingly, while continuing to drive with the battery not charging I didn’t experience the jerking at all, but when the dash would flicker back on I almost immediately got the flashing CEL and jerking. When I got to the office and parked, all levels resumed to normal. I turned off the vehicle and was able to restart. Applying some gas in Park and voltage spikes again. I’m not sure if this is due to adding that direct ground from the alternator to chassis/battery neg, but that’s the only real change I can think of. I’ll pull it off later and test it to see if that’s impacting.

At this point it seems like it is an RVC issue, even though I don’t have a standalone. I did some reading and it looks like the RVC system that’s internalized uses communication between the PCM and BCM to regulate voltage. Any thoughts or insight on that? Seems like my BCM is completely losing communication with the PCM when increasing RPMs above idle.

Also popped the hood when I got back to check things out and there’s a definite smell around the battery. Wouldn’t be surprised if it’s shot, as it was running at almost 17 volts for a bit.

 

[MTBoss]

Quick update:

This afternoon while at work I checked to see how the voltage levels were and it appears the alternator is shot after this morning's excursion. Got a "Battery not charging" message across the dash and the red battery symbol in the upper right corner, which is the same thing that happens when you pull the 2-wire signaling plug from the alternator. I checked that as well to be sure it wasn't burned up, and got 5V reference on the Red lead. Likewise, meter showed no juice coming from the alternator, and I tried revving a bit to see if there was any change. Ended up charging the battery as much as I could off of a jump and took my chances on the road home. Battery is fairly new, and I was actually able to drive it 39 miles before it died in my driveway. About 2 miles before getting home all of the interior components cut out, and then the headlights as I was turning down my street.

Was on the fence with the alternator anyway, so gives me an excuse to return it (bought on Amazon) and go with a higher quality unit. I'll probably bring the battery in to the auto parts shop and see if it's shot as well.

Really fortunate things didn't go worse today; felt a little reckless continuing on after the voltage spiked up. And in a way, it seems like this may have given a little more insight into what's actually causing the initial issue. I think I'm going to pick up a used BCM and see if replacing that gets me anywhere. Any thoughts on that?

 

[MTBoss]

Feels like I’m beating this post to death

Just swapped out the alternator with my original and now it seems to be working again without issue. Haven't taken it on a long drive yet to see if the original problem surfaces, but it seems to be charging properly, although a bit lower (13.5V vs 14.4V.)

Also poking around on the Tech2 and wanted to see if anyone could verify a couple voltage values for me. Vehicle running:

EC Ignition Relay Feedback: 13.2V
Ignition 1 Signal: 13.4V

Couldn’t find any reference values for this engine, but saw a list that showed a 2.25-2.95V expected value on EC feedback for the LS2. Update: Found Ignition 1 Signal reference.

 

[mrrsm]

You might consider trying to use your Tech 2 to confirm what @limequat covered regarding a Completely FUBAR’d PCM:

(1) Have a Passenger available to Hold the Tech 2 and Watch The screen while you Test Drive the Vehicle under conditions likely to cause the sudden Engine Code Light to come on while the vehicle lurches.

(2) Plug in the Tech 2 into the SUV DLC and after Setting up the Tech 2 as Follows...

Diagnostics→Vehicle Year→ Vehicle Type (Light Truck) → Chevrolet Truck→ Product Series (S) Trailblazer → Diagnostics (Vehicle Control Systems) → 4.2L → Vehicle Identification → (Choose either Up-level Radio or Navigation Radio) → Establishing Communications → Vehicle Control Systems → Class 2 Message Monitor → Waiting for Data → Class 2 message Monitor (Ping ALL Modules)

… Start the Vehicle and conduct your Test Drive.

(3) Have the Passenger keep their Eyes GLUED to the Tech 2 Screen just after they hit the “PING ALL MODULES” Key and advise you whether or not ALL of the Modules report in the Right Column as “ACTIVE”. What they are looking for is a COMPLETE change of ALL On Screen Modules from an “ACTIVE” State into an INACTIVE State just as the Vehicle LURCHES and advise you of any On Screen Changes to this affect.

(4) Also... If the Passenger observes any Individual Modules changing from an “ACTIVE” to INACTIVE” Status ...they should make a note of which Module went DEAD at precisely the moment of the LURCH occurring.

 

[MTBoss]

@MRRSM appreciate the info. I just ran a drive cycle and it did the lurch 4 times and we saw no change in any of the statuses. All modules remained active before and after pinging.

 

[mrrsm]

Okay... That would SEEM to take the PCM Off The Table as the Culprit... (But I would Side with @limequat 's Expertise over any of my suggestions... Hands Down) Your Next Port of Call might be to use @Realism 's Amazing Post to Chase down every single Ground in the Engine Compartment...and make Damned Sure to perform the "Touch...Twist and LIGHTLY Pull on the Copper Cables" in each and every location around and underneath the Engine Bay:

Electrical Ground locations

While troubleshooting a bad ground I came across some scans of the service manual regarding electrical ground locations for our platform posted on another site. This includes both short and long wheel base, as well as both 4.2L and 5.3L. Credit goes to Wex...

gmtnation.com

One other Thought comes to Mind... The Main Fuse Block Connections:

On rare Occasions... the "Blocky" Electrical insert points will have an Electrical Break in the Thick Copper Wires embedded into the Block Channels. Pull them all out from under the Power Distribution Center and then Use a Bright Light and a Magnifying Glass along with an SAE-ANSI Calibrated "Eye Ball" and look for any signs of Burning, Melted Plastic or Out and Out Broken Wires inside. These CAN be Repaired using some Silver Solder and Due Care... or it may come down to trying one from the Salvage Yard. Best of Luck with this issue, Brother.

 

[MTBoss]

@MRRSM: Excellent suggestion! I’ll definitely work through the grounds as outlined in that post. I did pull the fuse panel apart in the engine bay and took a pick to the copper wiring in the block channels looking for breaks and came up empty; although I didn’t quite inspect it as thoroughly as you suggested. However, there were some parts of the copper that had slight burn/discoloration though. I’ll see if I can snag a salvaged fuse block for cheap to at least eliminate that as the culprit.

Taking the original issue and comparing it to the event that happened the other day where the RVC pretty much ceased to function, I’m really thinking the connection between the BCM and PCM is what’s being affected here. As you’ve suggested, it could be ground related. Or could possibly be an intermittent short on one of the 5V references with the 12V main power feed at or around the BCM. Although I’m not sure if the Class 2 system would have showed the BCM go inactive or dead when I was testing that earlier if that were the case.

Appreciate your feedback sir! Electrical issues are fun.

 

[limequat]

I still believe the PCM is resetting. The PCM drives the speedo and and tach directly. It makes sense that they would start to drift back to zero and then jump back to real values.

 

[MTBoss]

I still believe the PCM is resetting. The PCM drives the speedo and and tach directly. It makes sense that they would start to drift back to zero and then jump back to real values.

Good point. Aside from verifying the ground to the PCM, what other wires/parts of the harness do you think would be good suspects for the PCM resetting? You thinking the PCM is resetting because it’s momentarily losing power, or momentarily surging power? It’s hard to tell if the voltage spike is preceding or following.

 

[limequat]

Chicken or the egg? Maybe the spike is caused by the PCM resetting. There's 3 or 4 power inputs to the PCM, all off of different fuses. There's also the possibility that it's internal to the PCM, or a software reset.
Back to MRRSMs idea for pinging the modules...it could be that a reset is occuring between pings. Depending on priority and bus speed, it could take 100s of ms to complete the pings. I don't know how long a SW reset would take, but it could be pretty fast.
If I'm right, you might need an oscilloscope to diagnose this properly. Or, get a new used harness and PCM and kill the issue dead. Either way, it's a lot of money to invest based on what some dude on the internet says.

 

[budwich]

pull the plugs / connectors at the pcm and check the pins on both. People have seen the pins having issues (ie. "misalignment", "corrosion"). such that they get strange events. Since everything that the PCM "sees" / "does" travels thru them, focus on those pins associated with powering / grounds.

 

[mrrsm]

... and while trying to run these Gremlins to Ground... Here are all of the Harness-To-PCM Pin-Out Diagrams and GM Class 2 Network Imagery to assist you:



These Two CRC Electronic Component Spray Solvents are your Best Friends in this situation. They are CHEAP and available on Amazon:


PS...

On Very rare Occasions... Alternator OVER-VOLTAGE Spikes can occur if the Rectifier(S) Panel has gotten 'Wonky'... PCMs and BCMs hate THEM as much as Under-Voltage circumstances. ;>)

 

[MTBoss]

Thanks again guys; these are good suggestions. Are the 4.2 diagrams backwards compatible with the 5.3?

 

[mrrsm]

Ouch... Sorry for this I-6 Oversight... No... The GM 4.8L, 5.3L and 6.0L Engines Do NOT use the ACDelco P-10 PCM... Here is what the Delphi V8 PCM Harness Connectors look like on that PCM:

 

[MTBoss]

Ouch... Sorry for this I-6 Oversight... No... The GM 4.8L, 5.3L and 6.0L Engines Do NOT use the ACDelco P-10 PCM... Here is what the Delphi V8 PCM Harness Connectors look like on that PCM:

View attachment 92869

No worries, and thanks for the reference photo. Do you know if similar diagrams for the pins are available for the 5.3? I can’t seem to find one among @Mooseman’s document post, at least on my mobile device. Maybe it’s in the 2006 service manual that’s a large zip file?

 

[mrrsm]

Yes... The Digital GM OEM Service Manuals are available (Courtesy @Mooseman) via THIS Link. I think they come in the PDF Format but any Zip-Unzip App should be able to extract them:

Need service manuals? Get them here!

*********************************************************** The password below is no longer required. I am unable to edit that post to remove that info. Please note that the FireFox browser has issues with the password handling and because these downloads are not under HTTPS, flagging them as...

gmtnation.com