P0690 Code help

[rcarson25]

So dialing in all of the gremlins on my 1978 firebird LS3 swap. All seems to be working well excpet that I am getting a P0690 ECM Power Relay High code. I looked at ECM fuse and it is good visually inspected the harness, as much as I could and all looks good. The car seems to start and run well. Any suggestions where to start on this? Common swap issues related etc? Thanks in advance.

[rcarson25]

I checked resistance in the 3 GMPP harness grounds and all seemed good. I checked other grounds on the vehicle just to be sure and those all seemed good as well. I also checked the ecm fuses in the GMPP fuse block and those all look good. I checked the battery and all connections seem good and it has 12.4v. I will check to see if there is voltage feedback when on next. Anything else I should be checking to chase down this issue?

[vette427-sbc]

What is your running voltage? Measured at battery and at the ECM

[sccacuda]

Not sure how GM defines codes, but for Mopar, high means short to voltage. If the same, it would mean the relay is staying powered when the ECM is expecting no voltage on that relays output. Maybe something as simple as having the relay coil wired to constant voltage when it should be ignition switched voltage.

[rcarson25]

Will check my running voltage today. Excuse my ignorance here, but I don’t see a PCM relay in the GMPP power block. Would the PCM relay be the same as the PT Relay, does anyone have the pin out or wire diagram for this relay?

[rcarson25]

Voltage while running at the battery is 14.4v I do not have a back probe to test at the pcm. May need to pick those up.

[rcarson25]

So, couple things I realized that may help someone else out in the future.

PT Main relay controls fuse position 1,2,3,7,8,9
Ign relay controls fuses 4,5,6

The PCM fuse is fuse 4 and is controlled by the IGN relay. Guess what happened when I switched that relay out......No more code. Thanks for all the help guys now on to the next item on the check list.

[rcarson25]

Thought al was fixed and light came back on. I am thinking it is an issue with the wiring to the ignition relay. I have searched with no luck does anyone have the wire diagram or pi out for the ignition relay?

[ween]

From old notes:
Powertrain relay: Terminal 30..Battery, Terminal 87..Fuses 1,2,3,7,8 ,Terminal 85..Fuse #5 (ignition relay out) , Term 86..PCM Blue connector pin 40

[rcarson25]

thaNow, do you happen to have the pin outs for the ignition relay as well?

[ween]

Ignition relay: Terminal 30..Battery, Terminal 87..Fuses 4,5,6 (MAF, relays, bulkhead), Terminal 85..Ignition switch (12volts run and start), Terminal 86..Ground

Fuel Pump Relay: Terminal 30..Battery (maxi fuse 2), Terminal 87..Fuel Pump (grey lead), Terminal 86..ECM blue connector, pin 13, Terminal 85..Ground

[rcarson25]

Awesome, thank you so much

[rcarson25]

I did some probing on the relay circuits and though I am getting 12v to the constant I am only getting 11.6v to the switched, which is 86 for me, 85 is my ground. I don’t think this matters as they are opposite sides of the could. I am going to check my switched ground connect under the dash but figure this would be a good place to start. I assume the pcm may not like the .4v drop and that may be one reason, if not the reason, my MIL is on?

[blitzer454]

I haven't incurred this problem myself but here's some things to try:

1. remove the IGN relay and measure the voltage across terminals 85 and 86 with the ignition switch on and off. With the key off you should get 0V and with key on you should get around 12V.

2. repeat test 1 but this time put the negative test lead of the meter on the battery's negative terminal and the positive lead on terminal 85. The voltages should be about the same as test 1. If they are then you have good ground to the fuse block if the voltage is 3V or more higher than test 1 then you have a bad ground.

[rcarson25]

12v constant 12.42v

1.) key off 0v key on 12.25v
2.) grounded to battery key off 0v key on 12.25v

My terminal 85 is ground and 86 is switched 12v. I don’t think this should be an issue because it is just opposite sides of the really coil correct?

[ween]

Yes, you are correct. i believe the relays GM uses have a suppression resistor in them, not a diode.
The coil therefore isn't polarity sensitive.

[rcarson25]

Did more tests yesterday. All seems to be working as it should at the relay. I tested the wiring at the fuse block and all seems good for pin 30, 85 and 86. I did a bunch of tests on the wire for pin 87. With power off I get continuity with the positive post of the battery and an open circuit with the negative post. When looking for voltage I get nothing when testing to negative post. All of this seems to make sense, what I don’t get is why I get a full 12v when I test voltage from pin 87 wire to the positive post of the battery. Does this sound right? I would think if I had a short in the wire I would get continuity with ground, no?

[rcarson25]

Also tested PT relay to see how it looks:
Ignition off: 30 12v, 85 0v, 86 open circuit 0v, 87 7.5v
Ignition on: 30 12v, 85 12v, 86 ground, 87 6.3v

Does that all sound about right?

[blitzer454]

All of this seems to make sense, what I don’t get is why I get a full 12v when I test voltage from pin 87 wire to the positive post of the battery. Does this sound right? I would think if I had a short in the wire I would get continuity with ground, no?

It sounds right, if that is the voltage you measured when the relay is off. When the relay is off you're measuring the open circuit voltage between those two points and when the relay is on that voltage should go to 0V.

The documentation that I have read concerning this code is that there is a fifth voltage sense wire that goes from the ECM to the relay that the ECM uses for this test but I have been unable to determine which pin on any of the ECM connectors is used for that wire nor did I find any info as to which relay terminal it's connected to. The test says that a voltage greater than 3V when the relay is off or greater than 18V when the relay is on will set the code after it persists 5 times. If a guy knew where that wire was he could leave a probe on it and see if it ever meets the requirements to set the code.

[rcarson25]

Now I feel like you are just teasing me.....Would be nice if GM would provide an actual wire diagram with these connect and cruise packages.

[ween]

There shouldn't be that much voltage drop across the relay contacts
Ignition on: 30 12v, 85 12v, 86 ground, 87 6.3v
The voltage at terminals 30 and 87 should pretty much be the same with the relay operating.

[rcarson25]

So I re ran the checks as suggested.

Ignition on: 30 12v, 85 12v, 86 ground, 87 12v
Ignition off : 30 12v, 85 0v, 86 open circuit, 87 7v.

I tested the wire that comes into the fuse block at 87 with the relay out of the fuse block. There is 7v there when the car is off and 6.3v when ignition is on. Should there be voltage at this wire with the car off? Does low voltage there when off indicate a short or a back feed?

[ween]

I'd have to check on a similar system. The voltage checks would normally be done with the relay in circuit.
GM tells you to use 2011 or so Camaro for service information. The powertrain relay is wired differently in the Camaro compared to the GMPP.

[ween]

Checked on a vehicle in shop today, had LS7. Removed Powertrain relay, cycled ignition, left off, probed terminals.
Term 30 12.7V, Term 87 0V, Term 86 12.6V, Term 85 0V. Cleared P1682 code afterwards.
This vehicle has the GM trans computer that plugs in to the bulkhead connector.
I feel something is suspect with your harness. Is there anything connected to your bulkhead connector?
According to GM instruction sheets, the LS engine control kits all use the same engine harness.

[rcarson25]

Kind of as I suspected I seem to be getting some sort of power feed back into the harness. Of course the bulkhead connector in question is buried deep within the fender well and will not be easy to get to. Would have to pull the whole fender to get to it . Thanks so much for the confirmation, I assume that 6v I am seeing at the pin 87 wire with Ignition off is my issue. I will track it down and at least I know where to start. Any clue what in the bulk head may tie to the wire that feeds pin 87 on the Pt relay?

[ween]

Can't say. Quick test would be to remove the fuses labeled bulkhead in the GMPP fuse/relay box though.

[rcarson25]

Yeah I plan on pulling some fuses to help track this down. Hopefully I can track this issue down.

[rcarson25]

So after testing a few fuses and relays I think I have found the issue. Relay 3 for the dual fan setup has a constant 12v wired to pin 86 and it should be a 12v switched. When that relay is out of the equation the P0690 and the 7v at pin 87 of the PT relay is gone. Have to open up the fuse block and change the wire, fingers crossed I can get to it without taking too much apart.

[rcarson25]

Made the change in the fuse block and all is good. No more check engine and no more phantom voltage at the PT relay. Thanks for all the help.