SOLVED! Crankshaft Position Variation Relearn issues

rchalmers3

Gold Supporter
Hiya fellas, I'm currently struggling with getting my workhorse back on it's feet after removing the engine for resealing and refreshment. It's a 2005 Sierra 1500 2wd, base cab long bed with 370k miles on the 4.8L engine. I believe you folks know this truck as a GMT800, but I'm just learning to speak Chevrolet.

After installing the freshened engine, it starts, runs and drives, but has all of the symptoms of needing a crankshaft position variation relearn. I could numerate the various driveabilities, but I think you fellas are all aware of what those symptoms are. BTW, there are neither those "P", "B", nor "C" codes that are known to inhibit the relearn procedure, nor am I seeing the two "p" codes directly relating to the CKP sensor. Nothing. Zip. Nada.

The specific issue is that neither my Snap-On Verus or my Maximus 2.0 scanners can perform the relearn procedure. The Maximus 2.0 takes me into the procedure, but there is no rev limiter (yikes!), and time after time the procedure does not complete successfully. Meanwhile the Verus won't initiate the test. The scanner displays an error message indicating the test is "out of range" due to the "transmission is not in park or neutral."

Since the range switch is on the side of the transmission, and easy to access, I have tried moving the switch to the limits of it's adjustments, and have swapped in a known good switch. These easy attempts to affect any improvement in the test results proved fruitless. Because the instrument cluster gives correct shift position readings while selecting gears, and is displaying what the ECM is seeing from the range switch, I'm left to believe this is an ECM issue.

This is a puzzle I'm unable to solve all by my lonesome self! Before I head down the road of an ECM repair or replacement, I'd like to hear from the brain trust. Do you guys have any insight as to why the ECM won't conduct the relearn process? Any experience or advise is appreciated. Thanks,

Rick
 

Mooseman

Master Blaster
Moderator
Usually a cam/crank correlation errors happen when a CASE relearn is needed but it should still do it regardless. Do you have access to a Tech 2? It might have better luck.
 

rchalmers3

Gold Supporter
Thread Starter
Thanks for the suggestion, I do not have the Tech II. However I recently made a friend at the local $tealership. He is a transmission specialist, and happens to be a GMT360 fan like us. I’m thinking I might approach him to see if he’s available on the side.

Meanwhile, it appears the ECM has been previously repaired. There is a sticker on the unit from a company that offers ECM repairs on EBay. I have contacted them and will report their response to my query.

Rick
 

MRRSM

Lifetime VIP Supporter
Still "Stock as a Clock" inside? Visit THIS Link to get the Down-Lo on the "GYMKO" (General Motors Knock Off) Tech 2 offers. There may be some links that are still active to contemporary sales of these Scanners for around $300.00 via AliExpress Vendors:


We've had quite a few Members make their purchases successfully and remain quite satisfied with them. You couldn't tear mine away from my Cold, Dead Hands ...with a John Deere Tractor... :>)
 

TollKeeper

Gold Supporter
I thought we had a couple tech2 owners in the Carolinas?
 

rchalmers3

Gold Supporter
Thread Starter
Silly question, but did you have the park brake on while attempting the test? If not, this can inhibit the results. Ask me how I know.
Thanks Chickenhawk, I definitely had the PB set, and followed the procedure correctly. However, I'm curious to know what tool did you use? And how were you informed of the improper condition?

Fellas, I have an update: I visited the dealer and confirmed the service number on the ECM is applicable to my truck. My acquaintance at the dealer was disinclined to provide me with ideas or assistance. The company whose sticker is on the ECM had no ideas, other than to use a Tech II on it. But I'm not ready to hand the dealer a tall stack of cash.

I made a new observation that leads me to believe there is an internal issue inside the ECM. The underline that tracks the shift position on the PRND display functions, but the P and N positions lose the underline after about 5 seconds after engine start. They return briefly on a restart, but vanish quickly. All the gear position underlines (RD321) work steadily.

What say you? Am I wrong to ASSUME this observed behavior is Abby Normal?
 

Mooseman

Master Blaster
Moderator
I think that the PRND321 issue is a problem with the cluster itself. They have been known to go bad. Only way to confirm is with another cluster.

Thing is with PCMs, most of the time, is they either work or they don't. It doesn't sound to me like a PCM issue but something with the scanner not doing it right. I've used my Tech 2 for lots of CASE relearns and never had an issue except once where the jackwagon never really fixed the issue with the crank sensor throwing a code. He insisted I try and... Revved to 6500 RPM and didn't cut out. If you have no errors and it won't do it, I'd give the dealer a try with either their Tech 2 or MDS. It's literally a 5 minute process and tell them that's all you want. If you're lucky, might only charge for 1/2 hour or an hour.
 

TollKeeper

Gold Supporter
PRND321 could also be the BCM or Neutral Safety Switch. So dont read to heavily into that until you can get a definitive answer. Parts Bazookas are rather expensive!
 
My vote is a cluster issue for the missing indicator bar. For informations sake: the cluster displays the bar at the appropriate position in response to a serial data message from the PCM. Watch here as I spoof the messages using a bluetooth OBD2 adapter and a serial data app on my phone... (The click heard at the reverse position is a relay on the bare BCM board seen on the bench)

 

rchalmers3

Gold Supporter
Thread Starter
PRND321 could also be the BCM or Neutral Safety Switch. So dont read to heavily into that until you can get a definitive answer. Parts Bazookas are rather expensive!
Tollkeeper, the range switch is the same part number found on the GMT360 transmissions. I happen to stock some used switches, and tried two of them, with no changes in results. Skewing the switch full clock and counterclockwise made no difference. I also pinned out the 5 wires between the ECM and range switch. All is well.

Please consider, the truck does start only in P and N. I consider that observation to be evidence the range switch is working and reporting to the ECM.

Rick
 
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rchalmers3

Gold Supporter
Thread Starter
I think that the PRND321 issue is a problem with the cluster itself. They have been known to go bad. Only way to confirm is with another cluster.
Mooseman and TJBaker57, The cluster was repaired within the past year by one of those services found on Ebay. That does not guarantee anything, but based on the recent repairs, I am less concerned about the display, and more about where the information that drives the display comes from, ala the serial data line TJBaker57 mentions.

Guys, talk me through this: All 8 ECM grounds plus the transmission range switch use the G103 ground on the right rear of the engine. I remember making that connection fast due to the inaccessible nature of the rear of the head and block on that side. My interpetation of the range switch wiring schematic is that the range switch distributes a ground signal from G103 back to the ECM via 4 switch positions: A, B, C and P. If I'm understanding the schematic correctly, the ECM wants to see an ABSENCE of a ground signal on PRND A, B, C and P, in order to enable crank. Do you concur with my assumption, or shall I go outside tomorrow and confirm the computer grounds and range switch signals?

I still think the ECM is the culprit, and am trying to prove that hypothesis right or wrong.



Rick
 
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rchalmers3

Gold Supporter
Thread Starter
Found it! Between a ground splice connection in the loom and the range switch I found this broken wire on top of the engine.
IMG_0268.jpg
Thankfully the break was on top of the engine and not laying on top of the transmission. I was much more comfortable laying over the radiator core support than having to pull the loom from out over the transmission.
IMG_0267.jpg

There was no ground present at the transmission range switch. Without ground, all four signals to the ECM were default to 12v. The engineers get a big "attaboy" for arranging the switch logic such that the truck is still able to be started and driven in this failed condition.

The wire break was due to being tangled, making that particular wire effectively shorter than the other wires. I untangled the wire and created excess length before butt splicing it.
IMG_0269.jpg
I recovered the loom and have successfully performed the CKP Variation relearn, and I have all shift position indicators. Boy is it good to have my old, worn out truck back in operating condition.

Thanks fellas, I appreciate your thoughts and comments. This forum is a great place to propose issues and solutions to some sometimes vexing issues!

Rick
 

MRRSM

Lifetime VIP Supporter
Forgive this tiny o/t insinuation Rick...

But... in looking closely at your open hood image... it appears that your Rear Hood Weather Stripping Seal is a bit abraded:

ABRADEDHOODWEATHERSTRIPI.jpg

FWIW... This site carries the two replacements for your 05' Sierra for not too much bread... if it seems worth attending:


2005GMCSIERRAHOODSEALS.jpg
 

rchalmers3

Gold Supporter
Thread Starter
One last thought on this repair. In the FSM, under transmission diagnosis, there is a section on how to diagnose the shift indicator not working correctly. There you will find the data needed for a step by step diagnosis of proper range switch operations and logic. Turns out the ECM watches 4 circuits for a high (12v) or low (grounded circuit) in different combinations to determine shift position.

Finding that info put me on track, and exposing the ground loom splices gave me access to where that one broken wire leading to the range switch branched off the splice.

Thanks again,
Rick
 
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