E40 APP1 Mystery - 0V reported by ECU; 1-2.5V being generated by APP1

Settle in, this is a weird one.

I've don a lot of swaps over the years and this one is a real head scratcher/beard stroker :banghead:. Lucky me. You should know this car has been cursed from the moment that I got it, but that is not the technical issue at hand right now.


I am doing a swap into a non-GM platform using a 2005 Corvette Engine which I bought as a dropout; the transmission is a manual but is not from GM (which doesn't matter). The only changes to the PCM file is to make it a manual and do the patches, otherwise it is a stock file.

I am using a C7 corvette pedal which I know uses different voltage sweep patterns than the C6 that originally came with the car. The E40 pedal has APP1 rising from 1v to 2.5 v and APP2 falling from 4v to around 1v; most pedals after 2005 ( I suspect with the introduction of the 58x crank) have APP1 and APP2 rising, with one rising at roughly twice the rate of the other. The way I have my c7 pedal wired the APP outputs ARE CORRECT FOR THE E40.

Everything is wired up and I wanted to verify that everything was working but it wasn't. I have not yet tried to start the car, which I think has been a good call until this gets sorted out

The issue is that the PCM is throwing code p2122 which is APP1 low voltage. The throttle body basically locks itself in place and the PCM goes into REP.

When you scan the PCM it always shows APP1 reporting 0V, every-time always no matter what you do with the pedal. APP2 scans as normal.

--> The problem is that the APP1 signal which goes to C1 (Blue PIN 22) actually has the correct, expected voltage flowing through it, which I have verified many times by tapping into this wire with a voltmeter<---


I have checked the wiring many times and it is wired correctly.

The low references go to ground, the 5v signal wires come through to the pedal, APP2 works just fine.

The other 5V referenced sensors and the 12V referenced sensors seem to be working fine as well. The MAP sensor which shares the 5v bus with APP1 is working correctly and reporting the correct barometric pressure.

The PCM isn't throwing any codes related to this except for p2122.

The only thing that I can think of is that there is some sort of internal fuse in the PCM for APP1 and it was ether blown before I got it (The engine did come from a wrecked car) or I managed to blow it.

Has anyone ever seen this before?

It's more than just the voltages going in the correct direction as the pedal moves, they have to be within the expected window(s). 'APP1 Low Voltage' doesn't mean there's NO voltage, just that it's less than expected in those who-knows-how-many TAC tables we don't have access to.

I would plug in a C6 pedal and un-repin as required just to see if the rest of the system is able to work.

Possibly separate issue: How did you turn the auto trans tune file into a manual tune file?

The ECU is reporting 0.00v when scanning the APP1 PID even though the wire feeding pin C1 22 has between 1-2.5V travelling through it - that is the issue that I am trying to solve. APP2 is reporting the volage in the wire, when I switch the wires the other voltage is reported by the PCM (i.e. 1-2.5v).


Even though it doesn't do anything I changed the Transmission type from automatic to manual in the tune and then done a write entire - tried it both ways several times and it makes no difference.

What did you do with the T42 trans controller & wiring ? Normally, you need the GM dealer equipment to change from auto to manual and vice versa. Do you have the clutch switches wired in ?

I do not have the transmission controller and all transmission wiring has been removed.

All sensors are reporting voltages correctly except for APP1, including APP2.

If you tried to change the auto ecm to a manual ecm by writing, it still thinks it is an auto--with a bunch of inputs missing.

I have written the original stock tune into it (Which was an auto) and it makes no difference.

There are TAC and ECM bits in the TCM and TCM bits in the TAC and ECM. The things you've tried made no difference because HPT is not able to access two of the eight segments in the ECM, where those leftover auto trans bits are hiding.

What I would do...
-Re-pin as needed and plug in the correct APP, if it shows the same symptoms I'd be fairly confident the ECM has done broked.
-Get the ECM (either the existing one if it tests OK, or the replacement if it tests bad) flashed with a real proper honest-to-God flashing tool - i.e. not a HPT interface - like a Tech2. You'll need a VIN from a manual trans vehicle.

I should be able to test a stock APP later today; hopefully that will work but I doubt it.

If I am following this correctly if I had a 2005 Corvette Auto in front of me and unplugged the TCU it would behave the same. I need to have the PCM service flashed with as a manual transmission PCM. I Should be able to get that done in a few days.

So ultimately it is just like the old style PCMs except that the TCU is physically separate.

Hopefully I have that right.

Thanks.

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EDIT - I just installed a brand new 05 gas pedal and the PCM behaves exactly the same. That makes sense if the issue is the base program in the PCM.

As a follow up - the problem was simply the base service level tune :doh: :o . Once I service level flashed a manual transmission tune into the E40 PCM everything worked as it should, including the re-wired C7 pedal :cool: .

You do indeed learn something new every day.

Thanks for the help.

Another follow up - 1st this car is definitely possessed.

The throttle system worked perfectly yesterday. I disconnected the battery, went out to the car this morning and it is back to its old tricks APP1 reading of 0 volts.

For future searchers here is what should be the final follow up.

The problem was a BAD PCM

I replaced the PCM and the system is working perfectly with the C7 pedal wired as described above.

Also, the auto/manual service level flash had nothing to do with the problem; I tried the replacement PCM which was for an 05 Corvette auto and the system worked perfectly, then I flashed it with SPS to a manual and the result was the same.

I don't think anyone ever suggested that the '0v' issue was because of the auto/manual OS thing.

What happens when an auto trans OS gets 'converted' to manual by deleting the TCM is that the throttle behaves normally at key-on, but when driving the ECM is expecting to get feedback from a TCM, particularly regarding 'Abuse Mode', and stabbing the pedal while driving will result in limited throttle opening.

There are two ECM segments that HPT cannot access but the GM tools can. The ETC segments are different between a auto OS and manual OS. An auto trans ETC does not work right without the TCM reporting in that all is well. The manual trans ETC does not look for those TCM status messages.

Understood; didn't mean to suggest that I received any bad advice.

Now the fuel pump relay C1 pin 45 is always hot +12v whenever the ignition is on - another mystery.

I'm pretty close to moving on to an e38.

Quote:

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Originally Posted by rao

... I'm pretty close to moving on to an e38 ...

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Too funny. The E40 was used 1 year in the Corvette, and 2 years in other select models. They were not popular.

Changing from an E40 ECM is not a problem - however, they are a Gen 3 (24x CKP and 1x CMP) style controller. You cannot use an E38 ECM, unless you change the CKP and CMP reluctors and sensors.

The easiest (and most user friendly) option in a conversion vehicle, is to use a P01 or P59 PCM - depending on throttle body in use - DBC versus DBW. Back when 24x CKP LS2 engines were readily available, this was a commonly used control system.

It is pretty funny and a lot of work.

I understand that moving to an E38 would mean moving to a 58x reluctor and 4x cam gear and re-doing the PCM connecetors.