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.