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Thread: Clearing codes to run crank relearn

  1. #1
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    Clearing codes to run crank relearn

    I have an LS2 (2005 Pontiac GTO) in my Datsun. I believe I need to run the crank relearn procedure as I get codes for both the crank and cam sensor (yes, I replaced both). It runs smoothly after start up so I believe the motor is in time (I had an experienced machine shop do the timing). The main problem, apart from the codes, is that the motor doesn't like to start (it turns over, occasionally back fires, but eventually starts up and runs well).

    I tried to run the crank relearn procedure but it says it cannot run with codes present. However, I don't see any codes in the scanner (after clearing the cam/crank sensors). I'm new to HP Tuners so am I just missing something obvious?

    Thanks!

  2. #2
    Tuning Addict blindsquirrel's Avatar
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    Cam sensor is not working for whatever reason, probably miswired. Is there a reason you can't list the DTCs? Is it a secret? There are a lot of them and guessing is not really an effective method of troubleshooting these things. There are so many codes because they all mean different things and point you to different possible causes to look at.

  3. #3
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    I've checked the wiring for both the cam and crank sensors and confirmed they are wired correctly (I'm running a Wiring Specialties harness). I'll grab the specific codes this evening.

  4. #4
    Tuning Addict blindsquirrel's Avatar
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    (it turns over, occasionally back fires, but eventually starts up and runs well)
    This is the symptom when there is no data from the cam position sensor. The ECM only uses CMP to distinguish #1 TDC compression from #6 TDC compression. With no CMP signal it has to guess, once it figures out which of the two choices is correct, the engine runs normally.

    Not having the crank relearn completed will not set any codes other than P0315. And having any other CMP/CKP codes current will prevent doing the crank relearn.

    Are you certain somebody didn't accidentally stick a 4x cam gear in it instead of a 1x? Does your harness use any kind of extension harness for the front mounted CMP?

  5. #5
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    That's very helpful. Is there a way in VCM Scanner to see if the ECM is getting data from the CMP and CKP? I traced the current CMP/CKP wires to the FSM pinout but we did find an error in the original pinout so it is possible that one of the sensors is pinned to the wrong place.

    There is no extension to the CMP harness. I did have the machinist replace the timing set so I suppose it is possible that they purchased the wrong cam gear (specs are a 24x reluctor wheel, 1x cam gear). Can I diagnose the cam gear through the ECM or do I need to pull the CMP to actually look at the gear? If that is the problem, is there any solution other than replacing the cam gear?

  6. #6
    Tuning Addict blindsquirrel's Avatar
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    You can look through the cam sensor hole and see the pattern on the gear. If it's got the wrong one it has to be changed.

    I suspect, though I have not seen it first-hand, that if you were to combine a 4x cam gear with a 24x crank on a 24x ECM, you would get the hard/long crank symptom, and codes P0341 (CMP sensor performance) & P0016 (CKP/CMP correlation). And of course the P0315 because it hasn't been (& can't be) done yet.

    I don't know if VCM Scanner can show incrementing CMP/CKP counts, I have only looked at that with a Tech2, it's made for that sort of thing.

    Proper pinout is:

    CMP 'A' > ECM C2-44 +12v
    CMP 'B' > ECM C2-15 GND
    CMP 'C' > ECM C2-26 SIG

    CKP 'A' > ECM C2-62 SIG
    CKP 'B' > ECM C2-14 GND
    CKP 'C' > ECM C2-43 +12v

    See this? From GM's own 2005 GTO manual under Component Locator/Connector End Views:
    screenshot.24-02-2021 12.11.05.png
    ^^^ THIS. IS. WRONG, WRONG, WRONG.

    That's shown backwards from every other E40 CMP pinout. The diagram has it correct:
    screenshot.24-02-2021 12.17.18.png

  7. #7
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    I can confirm the pinout is proper (I have my notes from checking the wiring earlier). Early in my diagnosis I was getting the following four codes. After replacing the crank and cam sensors, it dropped down to two but I cleared the DTCs so I can't recall which two are still present (I can run the motor tonight and get the codes again).

    > 0x7E8: P0016 - Crankshaft Position - Camshaft Position Correlation - Bank 1 Sensor A (Pending, Current, Old)
    > 0x7E8: P0335 - Crankshaft Position Sensor A Circuit (SES, Pending, Current, Old, History)
    > 0x7E8: P0340 - Camshaft Position Sensor A Circuit (Bank 1 or single sensor) (SES, Pending, Current, Old, History)
    > 0x7E8: P0341 - Camshaft Position Sensor A Circuit Range/Performance (Bank 1 or single sensor) (Pending, Current, Old)

  8. #8
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    So it does look like the machine shop installed the wrong cam gear. I could clearly see the holes in the gear, which looks like the LS1 version. Ugh. At least I know the problem now...

    Thanks for your help. I would never have thought about the cam gear on my own.

  9. #9
    Tuning Addict blindsquirrel's Avatar
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    Ah, so they installed a 0x gear? lol (I mean, not funny, but kinda funny.)

  10. #10
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    It’s funnier from the outside, I’m sure! Apparently their parts guy was sh*t and has since been replaced. I guess it gives me an excuse to install a new camshaft while I’m in there...

  11. #11
    Tuning Addict blindsquirrel's Avatar
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    Apparently the exact same thing happened to this bear. How weird is that?!

    shop-installed-a-LS1-cam-gear-in-my-LS2.jpg