2007 4.8L with 4L60 (e38 and T42) swap harness - no pedal

[beenba]

I did a swap harness for a 2007 4.8L with 4L60 (e38 & T42). I'm having an issue when ignition is put on APP/TB is working fine, but once started 9/10 times it goes into REP (reduced engine power) and gas pedal drops out dead. When it does work, the engine runs and drives fine with zero issues.

When pedal drops out it seems to throw a P2123 code (APP sensor 1 voltage high), and fuel pump stops priming. Not sure why.


Tests done:
--logged the ecm supply voltage is steady at 5.1v
--logged both APP1 & APP2 signals and voltages are sweeping fine. TB1 TB2 also responding properly.
--tried 3 gas pedals, 2 throttle bodies.
--checked all wires from pedal to ecm, and wires from ecm to TB.
--harness grounds look fine (one by ect sensor, and one by TB)

--put a stock tune on e38 ecm, with just vats disabled, and issue still remained.
--tried another ecm, with just vats removed, issue still remained.
--disconnected the TCM, and issue still remained.

I'm at a loss here, not sure what else to check.
What else could cause it to be going into REP mode?


Log file attached with it working with just ignition on, then dead once started.wes_log_nothrottle.hpl

[beenba]

Bump!

[ScarabEpic22]

What pedal, throttle body, and ECM OS are you using? Are they all from the same vehicle? If not, you'll likely have issues. Post up your tune and also what pedal you have.

[beenba]

Yes the pedal, TB, and ECM are all for 2007.5 model year truck.

Pedal is ACDELCO 25832864.

ECM is 12597121
OS of the tune is 12714088
Seg 7 of the tune is 12605899
Seg 8 of the tune is 12590068

I've checked these against TIS, and they are all the latest offered for the VIN.

[2xLS1]

More information on the swap harness. Commercial or home made?

[ScarabEpic22]

What 2xLS1 said, how is the harness setup? We'll also need a tune in additional to the log from your first post if it's not a wiring issue.

[beenba]

I modified the factory harness. I'm not ruling out a harness issue, but here's what I've tried:

To rule out bad grounding (I've heard this could be issue) I cut the main ground on the ecm pin 73 and wired directly to battery negative with no change.

New APP and TB connectors soldered in.
Ohm'd out the 6 APP wires, all are fine.
Ohm'd out the 6 TB wires, all are fine.

Sorry I can't post tune, as it is in .cal format for another program, but I'm very confident it's not a ecm/tune issue as this happened with two separate 2007 ecms using stock tunes (with only vats gone).

Not sure what else to check other than harness issue. Maybe a bad sensor on the motor causing a issue with the 5v bus or grounding in the pcm?

Ecm is getting battery on black 20
Ecm is getting ignition on black 19 & 47
Ecm is getting ground on black 73.

TCM is getting battery on 32
TCM is getting ignition on 31
TCM is getting ground on 49.

[Jon S.]

Looks like you may have missed wiring 2 ignition voltage circuits when you reworked your wiring harness.


E38 ECM C1 (Black) pin 18.


T42 TCM pin 11.

[blindsquirrel]

My info for 2007 Silverado shows both ECM X1 #18, and TCM #11 (both are the same CKT 5985) as "Accessory Wakeup Serial Data".

[blindsquirrel]

#PIP3783B: Reduced Power Message And Accelerator Pedal Position Code - keywords 5.3 6.0 6.2 6.6 accel acceleration APP DIC DTC engine LC9 LMG LY5 LY6 L92 mode no P2120 P2122 P2123 P2125 P2127 P2128 P2138 RPM - (Nov 20, 2007)

Subject: Reduced Power Message and Accelerator Pedal Position Code

Models: 2007-2008 Cadillac Escalade
2007-2008 Chevrolet Avalanche, Silverado, Suburban, Tahoe
2007-2008 GMC Sierra, Yukon, Yukon Denali


This PI was superseded to update models and engines. Please discard PIP3783A.

The following diagnosis might be helpful if the vehicle exhibits the symptom(s) described in this PI.
Condition/Concern:

The customer concern may be a SES light on with a reduced power message.
Recommendation/Instructions:

Complete the current SI diagnostics for any symptoms or DTCs found. If the vehicle was brought in for a reduced power message and DTCs P2120, P2122, P2123, P2125, P2127, P2128, or P2138 were found, inspect connectors C109 and C205. Connector C109 is located on the left side of the engine compartment below the underhood fuse block. Connector C205 is located under the Upper Instrument Trim Panel. To access connector C205 use the SI procedures for Instrument Panel Upper Trim Panel with Windshield Defroster Nozzle Grille Replacement.

Inspect all terminal and pin fits at connectors C109 and C205. Make sure the connectors are properly seated and locked. Make necessary wiring repairs following SI procedures.

Please follow this diagnostic or repair process thoroughly and complete each step. If the condition exhibited is resolved without completing every step, the remaining steps do not need to be performed.

[blindsquirrel]

Per the P2123 diagnostics the only possible causes are: open ckt on APP1 lo ref (intermittent? see bulletin posted above), or short to voltage (unlikely, this would probably trigger other codes as well).

An intermittent open circuit is orders of magnitude more likely/common than a short to voltage.

[blindsquirrel]

And don't worry about the fuel pump right now, that's probably the ECM shutting the pump off when it sees the throttle fault. It's a symptom of the initial problem and not something that can be fixed on its own.

[blindsquirrel]

Last one, I promise:

If this thing were in front of me, and I couldn't wiggle and get it to replicate the open circuit while parked, I would patch in a temporary jumper between ECM X1 #30 & APP 'F' and drive it until I was confident it wasn't going to flake out again.

[blindsquirrel]

OK I lied. I'm slow sometimes.

...THEN, if it still flakes out with the jumper in place, I'd be very suspicious I had a bad ECM, but only because I'd know I had eliminated everything else.

[beenba]

Thanks for the info and advice. I ran new APP pedal wires when I had the truck in my shop, and nothing changed. I tried another APP pedal and same thing.
I'm wondering if its a bad APP plug....I did look at the pins but maybe they should be tightened up...it was a aftermarket gm plug with all white wires.

Unsure what the GM bulletin is having me check. I don't know what the C109 and C205 connectors do, and they are likely gone with it being a swap harness now.

[Jon S.]

My info for 2007 Silverado shows both ECM X1 #18, and TCM #11 (both are the same CKT 5985) as "Accessory Wakeup Serial Data".

On truck platforms GM used the term "Accessory Wakeup Serial Data" rather than using the phrase "the BCM will supply 12 volts to these circuits when the key is in the on position".

If you look at Corvette schematics, E38 C1 pin 18 is hardwired to ignition voltage.

I have seen people rework their own Gen 4 wiring harness, and mistakenly omit these two circuits, and have similar problems.

[blindsquirrel]

Well shit! I saw 'serial' in the pinout list and 'data communications' in the diagrams, and assumed they said what they meant and meant what they said. But noooo, that would be too easy!

[blindsquirrel]

Thanks for the info and advice. I ran new APP pedal wires when I had the truck in my shop, and nothing changed. I tried another APP pedal and same thing.
I'm wondering if its a bad APP plug....I did look at the pins but maybe they should be tightened up...it was a aftermarket gm plug with all white wires.

Unsure what the GM bulletin is having me check. I don't know what the C109 and C205 connectors do, and they are likely gone with it being a swap harness now.

A jumper at either J1 or J2 will tell you if this is a harness problem, or an APP connector problem. If it still happens with a jumper in either location, it's either the APP connector or something inside the ECM (or between the ECM connector & ECM pin, I guess, in other words it would have to be something beyond the location of the jumpers).

I do not think these low references are monitored in any way, so this test shouldn't create confusion for the ECM. It doesn't care or know whether a particular low ref pin is in use or not as far as I know.

[beenba]

On truck platforms GM used the term "Accessory Wakeup Serial Data" rather than using the phrase "the BCM will supply 12 volts to these circuits when the key is in the on position".

If you look at Corvette schematics, E38 C1 pin 18 is hardwired to ignition voltage.

I have seen people rework their own Gen 4 wiring harness, and mistakenly omit these two circuits, and have similar problems.

This could be exactly my issue then. The issues you have seen are related to APP codes also (or reduced engine power) ?

Per LT1swap they can be removed...so I'm pretty sure I did not connect those two wires to ignition voltage.


And thanks blindsquirrel if the above doesn't work I will try that. Stay tuned!

[beenba]

Both jumping the ground from the purple/brown APP wires and putting ignition voltage to accy serial wakeup didn't resolve the issue. Still no pedal and REP.

Last thing to try is wire up the PCM powertrain relay control (pin 59) to trigger the IGN wire pin 47 (pink black). Right now it is just wired to ignition. Maybe it needs to be controlled by the pcm and have the 3s shutoff delay?