I feel like it's getting harder and harder to find people who are actually knowledgeable, and good at their job. Not to mention thorough.
I'm on the Controls and Instrumentation side of things, so i get to deal with clowns all the time.
I feel like it's getting harder and harder to find people who are actually knowledgeable, and good at their job. Not to mention thorough.
I'm on the Controls and Instrumentation side of things, so i get to deal with clowns all the time.
That's because people aren't held accountable. Everyone gets a trophy. "Do as little work for as much money as possible." Hear it all the time.
Did not drive it yesterday but let it idle in the driveway while watching AC pressure and Fans and snugging down trans coolant and heater hoses.
Got the P1518 upon initial startup but didn?t come back.
Im getting ONLY P1518 and very randomly, I dont know what else to check other than open connectors and give the TAC, TB and PCM pins another visual.
All grounds have been checked, cleaned, torqued.
Power feed to the TAC has been verified. I have 1 single relay that feeds 6 fuses to power up the engine harness.
Since the TB connector on the harness had a jacked up pin, and giggling the connector (before I replaced it) would bring in this specific code, is it possible that it damaged the TB pin internally? Even though I can get pretty rough with it now and not cause a code.
I do have a spare TB I can swap out.
Is it worth opening the harness and making the serial connection a twisted pair? TAC is 6 inches away from the PCM with about 2 foot of harness so I can easily account for the loss of length after twisting, I would just have to shorten and re pin the other 14 or so wires.
At some point during tuning I did recurve the pedal table slightly to de sensitize the pedal on the bottom end.
I also had to tweak the throttle vs air flow table a small amount to keep the other diagnostic code from getting triggered (cannot recall the code but it?s the one that maxes out at 4.1). I setup a log and tweaked the table just enough. This code isn?t coming in anymore, just the P1518.
Last edited by wlwarnke; 05-16-2023 at 07:51 AM.
Compared to all the other things you've done and what's left on the list, how much effort would it be to put that table back to stock as a test? How many minutes' work?Originally Posted by wlwarnke
Yeah don't change the pedal stuff.. just asking for trouble.
Tuner at PCMofnc.com
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Big pain in the ass, especially on a theory. Seems more about cross-talk than electrical noise, so might be the solution. Have you verified that they aren't twisted pairs right now? Think you could use one of the twisted pairs from an ethernet cable, or make your own by chucking up two wires in a drill? Try to avoid re-pinning.
According to the GM diagrams, this is a UART signal and it doesn?t sound like UART need shielding or twisting according to a few websites on the subject of communication protocols. The length is also limited to about 15m.
At least 5 minutes. 😬
Refer to ?Intermittent Conditions? on page 2. Where is that?
I?ve read through this bulletin as it comes up on just about every search for P1518 diagnosis.
Harps heavily on power and grounds.
Have fun.
the most uselessly-generic page in the GM service manual Document ID 838866.pdf
Basically, 'check that everything in the vehicle is as it should be.'
May sound crazy, but have you tried a correct-for-application pedal instead of the diesel thing?
No I haven?t, I don?t have one but I used this same make and model pedal on a friends swap with no issues.
Yesterday was drizzly at home so super humid. May be something, may not, but the fault occurred just moving up and down the driveway. Swapped TAC and TB.
Opened TAC, TB and PCM connectors to inspect pertinent pins.
PCM, relays, OBD2, and TAC all use the same ground lug on the fender which also has a jumper added directly to the battery.
From battery to stud is like .5 ohms with a dmm. When powered up, I see like 11 ohms between battery and stud. This is probably just a DMM thing since you?re not supposed to measure ohms on a live circuit but still seemed odd since ground is ground.
I am really frustrated. I guess next I will run a UTP for the serial data or ?
My friend don't forget your training. Resistance means voltage drop.
While the engine is running, measure the voltage from the ground stud to the ground post. If you get nearly 0V you're golden.
Test in opposite, too. Compare pos-neg battery terminal voltage to pos-stud voltage. Should be nearly 0V difference.
Last edited by SiriusC1024; 05-17-2023 at 09:39 AM.
Measured voltage drop both directions. Nothing at 2 decimal places on my fluke. By nothing, I mean ?maybe? 0.01v.
Is cross talk a thing? I pretty much always have my laptop running. Maybe disconnect the OBD2 port for a test run?
It?s gotta be something stupid simple I?m overlooking.
Alternator noise?
Swamp gas from Venus?
Yeah crosstalk is a thing, especially over longer lengths of wire. I figure Gm spec'd twisted pairs for a reason. I don't have any ideas otherwise.
This evening I?ll swap out the 2 UART wires for a twisted pair. Outside the loom, completely separate.
Any idea if the factory UART is ran with UTP?
Nope lol I don't.
Just test ran with a shielded twisted pair, yes, only shielded on one end.
Still got P1518 a few times.
Putting that back, and moving on to something else. May run a dedicated ground just to the TAC module?
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