LLY P0335

[CaptPhil]

Well the old girl let me down finally. Truck ran fine, sat for a month then no start.

Gives about a 2 second crank, then stops. Code is P0335, crank position sensor. I've read about every thread there is online about this. Scanner shows no rpm during crank. Reluctor wheel is solid.

Replaced the sensor and pigtail. No change.
Pulled fuse box, found multiple mouse chewed wires, fixed. No change.
Checked all 3 wires for continuity to ecm, all are good with low resistance.
Jumped 12v feed from another circuit, no change.

If i probe any of the connector wires and touch a battery positive i get voltage, which i wouldn't have expected. But same with other harnesses.

12v wire is not getting voltage from the ecm, even though continuity is good.
Signal wire has good continuity.
Low reference is good to ecm.
Ecm is grounded.
All fuses are good and have power.
Batteries are new.
I can't back probe the ecm connector with my current meter, probe are too big.
All three wires show some continuity to ground, but so do other sensors harnesses.

Bad ecm? Short killing the 12v circuit?

I'm lost, been playing with it for two full days.

 

[Ron Nielson]

12v wire is not getting voltage from the ecm,

The crank sensor power is a 5V signal from the ECM, not 12V. Don't put 12V on a sensor wire unless it really requires 12v.

 

[2004LB7]

Back probe the connector with a paper clip or needle. Be creative

 

[CaptPhil]

The crank sensor power is a 5V signal from the ECM, not 12V. Don't put 12V on a sensor wire unless it really requires 12v.

I'm getting conflicting info on that. The LBZ is 5v, but everything I'm reading says to expect 12v from the lly.

Plus, the voltage wire is continuous to c-2 pin 28, which is a 12v supply wire.

 

[2004LB7]

LB7 and LLY use 12 volts for cam and crank sensors

 

[Ron Nielson]

I stand corrected. Thanks for that.

 

[CaptPhil]

Well now I'm confused more. I checked the cam sensor, it's getting 5.0v, even though according to the ecm pinout it's a 12v supply. Confirmed continuity to the ecm. Back probed and it's 5v.

Crank 12v supply is 0v back probed while the ecm plug is in and key is on.

 

[CaptPhil]

Jumped crank power to a 12v supply and got it to turn over longer, rpm were showing but jumpy, didn't start. Then back to normal.

 

[2004LB7]

What are you getting for missed crank and cam pulses count?

 

[CaptPhil]

What are you getting for missed crank and cam pulses count?

Not sure how to see that info. I'm using my v2. Haven't used the laptop yet.

Ecm is definitely not supplying 12v to the ckp though. But wiring continuity is very good to ecm pin from ckp.

At this point I'm leaning towards an internal ecm short that killed the 12v feed. I did have several mouse chewed wires under the fuse box. Will probably just pull the ecm and send it out to get bench tested.

 

[Chevy1925]

Dod you check all the power and ground supplies to the ecm? Test all the fuses?

Could be a bad ecm but its more likely you have power dropped to the ecm or bad pin connections. I would verify the pin on the ecm does not have 12v coming out with the connector removed (test directly at the ecm pin). If no power, I’d make sure every power and ground feeding the ecm is good. Also make sure no pins backed out.

Another thing to think about is load testing the wires you ohm tested

 

[2004LB7]

James has a good point. There are more then one 12V feed and ground on the ECM. I believe one or more of those is for supplying the 12V sensor and other accessory power. So, if you loose one or a ground, the ECM may seem to be working in all other respects but not have power for the sensors as you see

 

[Chevy1925]

We fought shit like this on an LMM recently. I really wish you could get diagrams of the internals of the ECM so you could see where the power feeds come from but instead, we get to fiddle fuck around and figure it out.

 

[CaptPhil]

Dod you check all the power and ground supplies to the ecm? Test all the fuses?

Could be a bad ecm but its more likely you have power dropped to the ecm or bad pin connections. I would verify the pin on the ecm does not have 12v coming out with the connector removed (test directly at the ecm pin). If no power, I’d make sure every power and ground feeding the ecm is good. Also make sure no pins backed out.

Another thing to think about is load testing the wires you ohm tested

I'll pull the connector and see if that pin gets power. I back probed it and verified continuity from the connector to the pin and to the ckp connector.

All fuses in the box have power and are good.

The ecm has power for sure, I can interrogate it fine with the v2. Plus pretty much everything else is working.

Should the ecm case be grounded? I am getting a ground across it to battery ground.

 

[Chevy1925]

The ecm has power for sure, I can interrogate it fine with the v2. Plus pretty much everything else is working.

Should the ecm case be grounded? I am getting a ground across it to battery ground.

Just because you can talk to it via the v2 does not mean all the powers are working. Again, in the case of the lmm we just fought with, it could communicate with scan tools, take flashes, operate as normal but the fpr and turbo vane actuator had no power/control and set codes. One of the multiple power “in” wires to the ecm had a bad connection within the ecm connector to the ecm. Only way you could tell was by wiggle test and seeing when the fpr came back on line.

So until you confirm it, dont assume.

As for ground, do NOT do that. There is a shared ground in the harness and if you have a bad ground, you are going to send a high load through the ecm in a way its not intended.

 

[CaptPhil]

Just because you can talk to it via the v2 does not mean all the powers are working. Again, in the case of the lmm we just fought with, it could communicate with scan tools, take flashes, operate as normal but the fpr and turbo vane actuator had no power/control and set codes. One of the multiple power “in” wires to the ecm had a bad connection within the ecm connector to the ecm. Only way you could tell was by wiggle test and seeing when the fpr came back on line.

So until you confirm it, dont assume.

As for ground, do NOT do that. There is a shared ground in the harness and if you have a bad ground, you are going to send a high load through the ecm in a way its not intended.

I wasn't intending on grounding the case, just pointing out that my meter going to battery ground and the case itself is showing ground continuity. So the case itself is grounded. Wasn't sure if it should be.

Which pins are providing ecm power? The battery positive voltage pins on connector c-1?

 

[CaptPhil]

Checked voltage at the ecm, both 12v inputs are getting proper voltage.
Main ground on c2 is solid, as is the ground in c1, but when I turn the key on its going from roughly 1 ohm to 30 ohms. So not sure what's the situation with that.

I am getting 12v from an unused pin in c2, wonder if I could repin the ckp 12v in the connector.

 

[Ron Nielson]

Use a jumper wire to start with, de-pin if you have good results.

 

[CaptPhil]

All three wires have ground continuity with the ecm plugged in and key off.

With ecm unplugged they are open, so that rules out the harness to the ecm.

I pulled the ecm and am not getting ground across the ecm pins, so there's gotta be a short to ground somewhere else.

God I hate wiring and ecms.

 

[2004LB7]

All three wires have ground continuity with the ecm plugged in and key off.

With ecm unplugged they are open, so that rules out the harness to the ecm.

I pulled the ecm and am not getting ground across the ecm pins, so there's gotta be a short to ground somewhere else.

God I hate wiring and ecms.

You might also have a misunderstanding on the difference between a "short" and an "open" when it comes to electrical. Knowing the difference helps greatly in diagnosis