Replaced plugs, cleaned TB, now have reduced power and SES lights.... :(

[Ed H]

I have been reading many threads and will continue, but I am hoping someone will chime in with a similar experience. I changed the plugs and cleaned my throttle body today. The TB was absolutely filthy, and I may have been a little hard on it (holding it fully open while cleaning)? Never had an issue with other cars. This is my first Trailblazer.

I disconnect the PCM fuses for 30 minutes, went to start her up and it would not crank. Dash lights and headlights were on, the battery had full power, but no crank. Disconnected the PCM again for about 1 minute and got her to start, but the SES and REP lights are on. The car idles over 1000, then almost dies, then back to 1000 again. Pressing the throttle pedal results in no change in engine rpms.

Did I toast my throttle body? The harnesses appear fine, all sensors are connected, etc. Does anyone have any ideas short of my brining it to Firestone? I can get to Firestone without a tow, but not to the dealer (max speed is like 10 mph)..

So much for a quick afternoon plug change and TB clean...

 

[Ed H]

Nope. PCM fuses pulled for 30 minutes and the engine would not crank. Pulled PCM fuses again for about 20 seconds, inserted, and it fires up again, but I have both SES and REP lights again. Pressing the throttle does not change the rpms. It changed the 'sound' if you will, but the rpms stay pegged at 1200.

I did go heavy on the throttle body spray. Any chance that got somewhere it shouldn't?

I also noticed the 2002 throttle body is different than 2003+. Did GM fix an issue with the 2002 design?

Appreciate any and all input....

 

[jrSS]

Did u not take throttle body off and clean it???? Id hope so. Or did u clean it while it was still bolted on?

 

[c good]

On a new direction, what type of plugs did you install? Also, did you make sure the Coil over's fit correctly on the plugs? Have you run a scan to pull the codes?

 

[Ed H]

Yes, I did unbolt the throttle body to clean it. It's pretty straightforward. (4) 10mm bolts, the wiring harness, and the vacuum plug (?). Not much to it.

I installed AC Delco 41-103s. Everything went as expected. Only plug #1 gave me a little challenge with the wiring harness covering the coil pack bolt. I am 99% sure I got the coil pack onto the plug. I would be 100%, except you have me thinking maybe I should pull it and check again... The coil pack fit fine, it was just accessing the bolt. It will take me 10 minutes to check in the morning. Hell, I will pull all of them just to be 100% certain.

I am somewhat encouraged you didn't immediately say I toasted the throttle body - as if it was a known issue on 2002s...

Also, I do not have a scan tool. I will pick one up in the morning.

 

[jrSS]

Well then too much tb cleaner shouldnt be at fault. And yea I know how to take out the i-6 tb. I used to have an i-6.

 

[Ed H]

I didn't mean to suggest you didn't know how. I am the rookie with i-6. Just proving I did.

 

[jrSS]

Its all good man.....let's just try to figure out what's wrong with ur ride.

 

[c good]

Good going on the AC Delco's. What was the reason for the service work? Was is running well before you started the work?

 

[Ed H]

It was running fine... I just bought the truck 3 weeks ago with 156k miles on it. This was "new to me" preventative maintenance along with air filter, oil change, etc, etc. You know how it is when you buy a new (used) truck.

The existing plugs looked pretty good (41-103s), but I had oil on #3. A topic for a different thread.

The throttle body has never been cleaned from the inside.. It was unreal (dirty) on all surfaces. Wow. I should post a pic..

I fully expected to start her up and purr like a kitten, but was unpleasantly surprised when it wouldn't even turn over when I turned the key. Only after a 'quick reset' of the PCM would it crank. I'll reseat all coils and pull codes tomorrow.

I appreciate your support. I am a newcomer to the i-6, but not to wrenching. This one really (unpleasantly) surprised me....

 

[CaptainXL]

it wouldn't even turn over when I turned the key. Only after a 'quick reset' of the PCM would it crank.

This should be your first clue that something isn't right with the battery or it's connections. For a vehicle of your age and apparent previous owners neglect of maintenance I would replace the bolts on the battery or clean them. Mine were almost totally stripped and the wires underneath the + and - boots were green with corrosion.

 

[Ed H]

I removed / replaced all coil packs, disconnected and inspected the throttle body wiring harnes (all appears good), and cleaned the battery terminals. Still had SES and REP.

I picked up a scanner later this morning and have 2 codes - P1512 Cnf and P1512 Pnd. I am researching now....

Edit: I cleaned-up the ground connections to the frame, cleared the codes, started her up, and now I am getting 4 codes,

P1512 Cnf
P1512 Pnd
P1516 Cnf
P1516 Pnd

Edit: It might be time for a new throttle body... The SES and REP lights come on immediately. Clear codes, unplug PCM fuses, and the codes come back almost instantly..

 

[gmcman]

Do you have any of this?


I would pull the TB harness and clean the contacts.

Did you inadvertently yank on the TB harness by chance? Could be a loose contact.

 

[gmcman]

I wanted to add.....did you get EVERYTHING cleaned where the throttle butterfly meets the TB bore? Even around the edge of the butterfly? I mean EVERYTHING?

Granted you pulled the fuse there is always the possibility you cleaned everything but left a spec of crud where the butterfly closes and is not allowing it to close, but cleaned everything else up allowing added airflow. Not very likely but figured I would ask.

The fact it didn't crank at first, double-check the battery connections, turn on your headlights, highbeams, rear defrost and when cranking observe the headlights. Do they dim slightly or heavily? Rear defrost may cycle off when cranking so I'm not sure.

I had my TB harness cut by a vandal a while back and when it was re-attached one of the crimps wasn't perfect. I would get occasional REP lights and I went back and re-cripmed everything and has been fine since. If there is ANY discrepancy with the TB the ECM says no go.

 

[Ed H]

I will check and clean the connectors again. I was pretty gentle with the wiring harness, but you never know. Been there, done that before. No fun.

I cleaned everything. It looks brand new. It was frankly disgusting. 156k miles (previous owner) and this was the first time the back side of the TB was cleaned.

I removed so much crap, the resting position of the butterfly might be farther closed that before I cleaned it. I am looking for help everywhere I can. Someone suggested I need the dealer to re-calibrate the throttle body and throttle sensors. Not something I can do without a top of the line scanner / programmer.

Appreciate the info. I will let everyone know the outcome so we can mark this solved and help others that run into this...

 

[gmcman]

There is a process involving turning the key on after disconnecting power but being on my phone I can't link it now. Do a search and try that .

This will allow the TB to relearn the closed point.

 

[Ed H]

At the advise of a mechanic, I disconnected the battery for an hour, reconnected it, turned the ignition key to the ON position, then slowly pressed the accelerator down to the floor (2 mins to get there), held it on the floor for 1 min, then returned to idle position slowly (2 minutes back). Did that 3 times. Then fired her up and let it idle 10 minutes. This didn't work.

GMCMAN, I searched for a while and did not find the post you meant, so I drove the car to Firestone at a top speed of 18mph. I did not want to risk a trip to the dealer at 18mph. I might not have made it there... And I need the truck back asap.

I will share the diagnosis...

 

[CaptainXL]

I read this somewhere.

Disconnect battery and wait for over 1 hour. Then reconnect and idle the truck without pressing any pedals for 15 minutes.

But since you don't have any codes then you probably don't have a throttle body issue. I would look into getting a vacuum reading. Should be steady at about 18 in Hg at idle.

 

[gmcman]

At the advise of a mechanic, I disconnected the battery for an hour, reconnected it, turned the ignition key to the ON position, then slowly pressed the accelerator down to the floor (2 mins to get there), held it on the floor for 1 min, then returned to idle position slowly (2 minutes back). Did that 3 times. Then fired her up and let it idle 10 minutes. This didn't work.

Like the Capt stated, I think what you did could be a problem. I looked but couldn't find the procedure but again, you turn the key to on, and don't touch the accel pedal, if you do you have to start over.

I believe the procedure the tech stated was with the GM TECH 2 scan tool attached but not certain.

Did you leave the rubber gasket installed on the intake? Was it there when you reattached the TB?

 

[gmcman]

I tried searching.....

 

[CaptainXL]

I tried searching.....

Let me check Alldata. It should be under the R&R procedure for the TB.

Edit: couldn't find anything.

 

[Ed H]

Did you leave the rubber gasket installed on the intake? Was it there when you reattached the TB?

Yes, the gasket was in place and remained there after I cleaned / reinstalled the TB. I have removed / cleaned TBs on other vehicles before and am not a complete noob (not meant to offend). I've done much more than this, again on other vehicles, but this one has me completely stumped.

I will be pissed if I should NOT have cycled the accelerator, but to be honest with you, I had little doubt it would work anyways. The truck did not need tweaking, this seems like catastropic failure of some component. My thought is the TB itself, but I won't know until tomorrow.

Also, I hear people can drive 30mph with the REP light on. Not me. The truck would not exceed 2k rpms, which I now know equates to 18mph (MAX) in first. The accelerator did not raise the rpms. It wouldn't shift. This is the worst "limp mode" as they used to call it, that I have ever experienced. No fun.

I will eat a huge slice of humble pie if it ends of being something simple / stupid. I hate humble pie. But I have eaten it before, LOL..

Edit - I did have a code - P1512 again.. Thanks again for your genuine support. That speaks volumes for this site.

 

[gmcman]

Have you checked the ignition switch?

Check the small ground wire going to the fender.

Everything worked before you took it apart, what was the order of disassembly? Did you disconnect the battery ground first?

I would seriously double, triple-check the connection at the TB. Make sure a pin isn't pushed back into the connector.

Edited to add: The reason I keep stressing the TB connection, I had the EXACT same issue you did when I had one wire slightly loose but making contact. Exact same symptoms.

Could be a powertrain control module, ign switch, bad TB but check the easier, cheaper things first. If anything is the slightest bit off with the signal to and from the accel pedal, TB and ECM, you will get a REP condition. Must be practically perfect.

 

[Ed H]

HELP! The truck is at Firestone. They confirmed the TB was toast. It was not sending open / closed information to the PCM. They replaced the TB and it is now sending a signal. HOWEVER, they are telling me it needs a new PCM because the sensors in the pedal are not communicating with the PCM. I told them no way. There is a re-learn procedure, or they should be able to program the PCM. They agreed to do more research for me on the GM tech website or something like that. Can someone advise / confirm how Firestone should proceed from here? I told them to let the truck idle for 15 minutes, and they said they would try that. I am NOT impressed with these guys. Per above, do you cycle the accelerator pedal or not? Does the PCM have to be unplugged for 1 hour? Firestone claimed they disconnected the battery for 20 minutes. I said that was not long enough..

Also, they have a Genesis scanner, and something else.

 

[gmcman]

Have you checked the ignition switch yet?

 

[Ed H]

No. I did not check the ignition switch. I dropped it off last night before reading your post. I did clean the ground-to-frame connections, but no improvement.

I removed / replaced the TB with the battery attached, and then pulled the PCM fuses. After encountering issues, I have removed the battery cable several times for up to an hour.

Firestone claims the TB was the issue and the new one "works" as shown on their scanner. They are not aware of a re-learn procedure, but only pulled the battery cables for 20 minutes. Long enough?

Edit - I refuse to believe the PCM is bad.

 

[CaptainXL]

I would just pay and leave with your new throttle body. Clear the codes and drive it for a while and see what other codes, if any, come up. If the same codes come back then it's their mess and you should demand your old throttle body back and a refund of your money.

 

[Ed H]

They claim codes 1512, 1515, and 1516. I am with you though. I will NOT pay for a new PCM. No fricking way.

 

[CaptainXL]

Sounds good. For future reference you shouldn't remove anything electrical without disconnecting battery first. Bad things can happen when you reconnect stuff. Especially if the ignition was left on. Oh well we all learn don't we.

 

[gmcman]

Someone else will probably need to chime in, but does the OP need a TECH 2 to readout the replacement TH?

Does this Firestone dealer have a TECH 2?

 

[CaptainXL]

Someone else will probably need to chime in, but does the OP need a TECH 2 to readout the replacement TH?

Does this Firestone dealer have a TECH 2?

Only GM dealers have Tech2's. They have special software and two way hardware capable of commanding specific tests. You don't need a two way scanner to passively read the throttle position.

 

[Ed H]

The mechanic just called. They still say PCM. They pulled the negative battery terminal for an hour, started the car, tried to program it, etc. The issue is there is no input from the app sensor now. Start car, mash gas, the rpms do not change. They are not seeing the app sensor move on the scanner. They do see the TB working, however. SES and REP lights remain on. The car is not driveable (over 18 mph) still.

Is a fried PCM possible? I did not have the ignition on when I disconnected the TB harness.

This is nuts. They are convinced its the PCM and I'm trying to juggle 10 things including a broken truck while at work... If the car is STILL undriveable (literally powered by "idle" only), I am stumped..

Edit - I may tow it to the dealer...

 

[gmcman]

I called my buddy and he said generally you don't need a TECH 2 to readapt. I guess they used one to see if it was communicating when mine was there.

I don't know what to tell you, I think you are tossing money at the wind if they aren't using a TECH2 but I don't know. Wish I could be more help.

 

[CaptainXL]

The mechanic just called. They still say PCM. They pulled the negative battery terminal for an hour, started the car, tried to program it, etc. The issue is there is no input from the app sensor now. Start car, mash gas, the rpms do not change. They are not seeing the app sensor move on the scanner. They do see the TB working, however. SES and REP lights remain on. The car is not driveable (over 18 mph) still.

Is a fried PCM possible? I did not have the ignition on when I disconnected the TB harness.

This is nuts. They are convinced its the PCM and I'm trying to juggle 10 things including a broken truck while at work... If the car is STILL undriveable (literally powered by "idle" only), I am stumped..

Edit - I may tow it to the dealer...

Wait. You just said in your earlier post that when they put in a new throttle that it works just fine?

So is the problem the pcm or the throttle body or the pedal position sensors?

 

[Ed H]

THE TRUCK IS RUNNING!!

Thanks to everyone for all your advise and patience. So I show up at Firestone and tell them I am taking the truck as-is. I will drive it home at 10mph and finish the job myself. They are perplexed. Why would you do that when it needs a new PCM. I told them it does NOT need a new PCM. They understood my frustration (as well during 5 calls throughout the day). So the Tech puts the intake resonator back on, fires up the truck, and backs it slowly out. I thought DAMN. Then he proceeds to drive around the building at a pretty quick pace. Faster than 10mph, and I could see him start / stop a few times. He comes back in absolutely baffled and says "The truck is running fine. The REP light is not lit, and I checked for codes - there are none". I literally yelled F-YES, I told you!!

It seems the truck needed to be started, idled, and started a few more times. I have no idea what they did, but they clearly looked (and felt) like idiots for telling me it needed a new PCM about 2 minutes earlier. The information they provided was unclear and somewhat contradictory. I think they were searching for a solution (on-line, etc), and their scanner was not a TECH II.

Thankfully, the saga is over and I have the truck back. Many lessons learned - #1 Do not manually rotate the TB open to WOT and hold it there while cleaning it.... #2 This board rocks. I thank you all. #3 Firestone is good for tires, but not stuff like this. If I can't figure it out, the dealer is the place to go.

Time for a couple beers!!! :wootwoot:

 

[CaptainXL]

Hey congrats! So it was the Tb then?

 

[Ed H]

Yes, it was the throttle body. I obviously screwed it when I held it at WOT position and cleaned the heck out of it. I am used to the old throttle bodies (direct cable). Lessons learned...

 

[BRomanJr]

Yes, it was the throttle body. I obviously screwed it when I held it at WOT position and cleaned the heck out of it. I am used to the old throttle bodies (direct cable). Lessons learned...

I'm thinking that holding it open could not damage it, Just fighting a spring. Many members do the same process to hold it open while cleaning. The problem may have been the wrong type of cleaner or massive amounts of cleaner getting into the electronics.

Either way, glad it's fixed.

 

[BRomanJr]

Only GM dealers have Tech2's. ........

Not true, The Tire Store I use for Tires and Service has a Tech II, They used it to re-program my new-to-me NAV Head Unit. They have the subscription to program all Modules too.

 

[Sparky]

Glad it wasn't the PCM. If it was that would have been one weird coincidence, unless you were hosing down the engine bay with the cleaner lol

I was warned when cleaning my TB to avoid spraying the cleaner towards the edge of the blade where it goes into the stepper motor area, just in case, and to air it out a few minutes before bolting it on and hooking it back up. If some got sprayed in there real good and got into its circuits, then energized, that may have been the cause, perhaps.

Hope that TB didn't set you back too far!