P0335 - good sensor and wiring; next probable cause?

[baskervi]

We have a 2007 Yukon XL 1500 5.3L with 220,000 miles. We're having a chronic problem with the crankshaft position sensor code lighting up, causing the Yukon to throw the stabilitrak warning and then goes into reduced power mode. I've spent several hours on it, I've taken it to the dealership and another auto repair shop. This may happen several times a day (usually 2-3 times per day), but it may work OK for a few days without displaying errors and going into reduced power mode. It even went a few months once without throwing any error codes or misbehaving (September 2017 through April 2018). The best guess from the repair shops is the PCM is flaky, although GM also wanted to replace the sensors again as well as the throttle body.

Here are more details: Both the CKP and CMP sensors were replaced with O'Reilly brand sensors last August, but the error code was still occurring. We replaced these with genuine GM sensors, but the problem still occured. This past weekend, I unwrapped the wire bundle from the PCM to the CMP and CKP sensors and visually inspected the wires, and I also flexed the wires to see if continuity would break or if the wires were shorted. There appear to be no problems. Looking at the reluctor wheel from a bore scope, it looks fine. Backprobing the CMP and CKP sensors and connecting to an oscilloscope, the sensor signals look fine (e.g. no missing pulses, but I'm not sure what the phase difference should be betweeen the CMP and CKP signals. I guess it's possible the timing chain could be stretched, but it did run fine for a few months with no problems. I've cleaned the connectors on each end with CRC Electronic Cleaner, as well as visually checked the connector contacts - some were very hard to see, but nothing appeared strange. I never lose connectivity when probing the connector, so I feel pretty certain the connector contacts are OK.

I'm not sure what to do next. We've already spent too much on this at the repair shop, and we've had 3 visits to the dealership, and the other shop kept the car a couple weeks. Does anyone have an idea of what I should look for? My best guesses are as follows:

1) Bad wiring harness connector to PCM
2) Flaky PCM
3) Stretched timing chain
4) Possibly put in a bad CMP or CKP sensor

I'd appreciate thoughts here. Thanks

 

[swathdiver]

Howdy Al. Do you know someone with a Tech2 or other advanced scan tool? You need this so you're not throwing parts at the problem.

Any aftermarket wiring put in the engine bay? It can cause interference. The next step after making sure the wires appear sound is to use the live plot to see that the crank and cam sensors are tracking together. The battery must be in good form too.

If it passes that then you check the harness connector with a multimeter across each terminal for ohms and volts and if they check out ok, it is your ECM that is the problem.

Since you've already replaced the CKP several times, my guess is you need a new ECM. But it could be the connector and or wiring or interference but not as likely.

 

[swathdiver]

1. Ignition OFF, disconnect the harness connector at the CKP sensor.
2. Test for less than 1 ohm of resistance between the CKP low reference circuit terminal B and ground.
 If greater than the specified value, test the low reference circuit for an open/high resistance. If the
circuit tests normal, replace the ECM.
3. Ignition ON, test for 4.8-5.2 volts between the CKP 5-volt reference circuit terminal C and ground.
 If less than the specified range, test the 5-volt reference circuit for an open/high resistance or short
to ground. If the circuit tests normal, replace the ECM.
 If greater than the specified range, test the 5-volt reference circuit for a short to voltage. If the
circuit tests normal, replace the ECM.
4. Ignition ON, test for 4.8-5.2 volts between the CKP signal circuit terminal A and ground.
 If less than the specified range, test the signal circuit for an open/high resistance or short to ground.
If the circuit tests normal, replace the ECM.
 If greater than the specified range, test the signal circuit for a short to voltage. If the circuit tests
normal, replace the ECM.
5. Ignition OFF, connect a fused jumper wire to the CKP signal circuit terminal A.
6. Ignition ON, momentarily touch the other end of the fused jumper wire to the battery negative post. The
CKP Active counter should increment.
 If the CKP Active counter increments, test or replace the CKP sensor.
 If the CKP Active counter does not increment, replace the ECM.

 

[baskervi]

I used an oscilloscope I had temporary access to, and I saw the CMP and CKP pulses on the same screen, so I did see the live plot. I even manually turned the engine and watched the CMP and CKP signals. I don't know of anyone with a Tech2 scanner. Will that provide other information than the oscilloscope? If so, I'll try to track one down. The tracking of the signals is what I meant by "phase."

You mention the battery being in good form. Fairly regularly, the battery gauge will show discharging. I took it into a local auto parts store, and I was told the alternator was bad. I replaced the alternator, but this didn't change anything. I've since taken it to a couple other auto parts places and had them check the charging system, and one said it was a bad battery, but this individual didn't appear to know what day of the week it was. I took it back and had it retested, and everything came back fine. I also went to another part store, and they also said everything was OK. I recently changed the negative battery cable, but that didn't change anything.

No aftermarket anything in the vehicle. All wiring is factory.

Shorting the remote connector and measuring resistance at the ECM connector, the reading stays consistent at .5 ohms, which is about what I get reading across the test leads. It doesn't fluctuate as I flex the wires.

Thanks for your assistance.

 

[swathdiver]

I used an oscilloscope I had temporary access to, and I saw the CMP and CKP pulses on the same screen, so I did see the live plot. I even manually turned the engine and watched the CMP and CKP signals. I don't know of anyone with a Tech2 scanner. Will that provide other information than the oscilloscope? If so, I'll try to track one down. The tracking of the signals is what I meant by "phase."

You mention the battery being in good form. Fairly regularly, the battery gauge will show discharging. I took it into a local auto parts store, and I was told the alternator was bad. I replaced the alternator, but this didn't change anything. I've since taken it to a couple other auto parts places and had them check the charging system, and one said it was a bad battery, but this individual didn't appear to know what day of the week it was. I took it back and had it retested, and everything came back fine. I also went to another part store, and they also said everything was OK. I recently changed the negative battery cable, but that didn't change anything.

No aftermarket anything in the vehicle. All wiring is factory.

Shorting the remote connector and measuring resistance at the ECM connector, the reading stays consistent at .5 ohms, which is about what I get reading across the test leads. It doesn't fluctuate as I flex the wires.

Thanks for your assistance.

Ok, well then, it seems you've done everything right so far Al. What do you mean though that the battery gauge shows discharging? Did you check the voltage on terminals A and C?

 

[baskervi]

1. Ignition OFF, disconnect the harness connector at the CKP sensor.
2. Test for less than 1 ohm of resistance between the CKP low reference circuit terminal B and ground.
 If greater than the specified value, test the low reference circuit for an open/high resistance. If the
circuit tests normal, replace the ECM.

==> I've not done this but will do it tonight.

3. Ignition ON, test for 4.8-5.2 volts between the CKP 5-volt reference circuit terminal C and ground.
 If less than the specified range, test the 5-volt reference circuit for an open/high resistance or short
to ground. If the circuit tests normal, replace the ECM.
 If greater than the specified range, test the 5-volt reference circuit for a short to voltage. If the
circuit tests normal, replace the ECM.

==> I've done this and got right at 5.0 volts

4. Ignition ON, test for 4.8-5.2 volts between the CKP signal circuit terminal A and ground.
 If less than the specified range, test the signal circuit for an open/high resistance or short to ground.
If the circuit tests normal, replace the ECM.
 If greater than the specified range, test the signal circuit for a short to voltage. If the circuit tests
normal, replace the ECM.

==> I've done this and got right at 5.0 volts

5. Ignition OFF, connect a fused jumper wire to the CKP signal circuit terminal A.
6. Ignition ON, momentarily touch the other end of the fused jumper wire to the battery negative post. The
CKP Active counter should increment.
 If the CKP Active counter increments, test or replace the CKP sensor.
 If the CKP Active counter does not increment, replace the ECM.

==> What size of fuse? I'll check this out tonight.

I post the response back tonight. Thanks

 

[baskervi]

Ok, well then, it seems you've done everything right so far Al. What do you mean though that the battery gauge shows discharging? Did you check the voltage on terminals A and C?

Sorry about that - I had a phone call come in and lost my train of thought. My multimeter normally shows 13.6 V across the battery terminals, but it drops down to 12.7 V when the battery gauge is reading on the lower side. This may occur for 5 minutes or so, and then it goes back to normal. I've not read any voltage levels on the sensor when the voltage gauge is reading low.

 

[baskervi]

I'll also note that I've not seen a correlation between the setting of the P0335 error code and lower voltage. I've specifically wondered about that, and we've been logging in a notepad every time this error code pops up, but at this time they've never occurred at the same time - they both occur about at the same rate, though - a few times per day on average.

 

[Tahoe14]

How old is your battery. If you have a dead cell it may not show up on the parts store testing equipment. Batteries can cause very strange problems.

 

[baskervi]

I don’t know the exact age. Maybe 4 years?