Hi, Just bought a 1988 5.0L in Freemont, CA and drove it to Fairfax, VA as an adventure with my kids! Car did awesome and my kids are so happy to have a trans am to drive (I am 52 yr old desert storm vet). AC is not working and ECU pin D11 is pushing 12v. and my right fan is not working. I expected D11 to be an input or a ground switch so the ECU knows the status of the second fan. Can anyone tell me if it's normal to see 12v on ECU Pin D11? Please help. I think I need to replace the ECU to solve the D11 voltage problem but wanted to see what others say.

 

D11 is both a fan request and a fan status input to the ECM. To the ECM it is a primary fan request.

But is also a signal that the secondary fan should be running.

In a no-fan-needed state, it should be at 12 volts (or system voltage).

With either the A/C high pressure switch, or the head temperature switch, being activated, D11 should go to ground.

Since the A/C isn't working, that can't request the secondary fan.

Which leaves the head temperature switch. In which the engine coolant needs to reach some absurd temperature of 228°F(?).

On a running engine you can ground the terminal of either the head switch connector or the A/C pressure switch connector and that should turn on the secondary fan. If not, then either the relay is bad, or the fusible link for fan power is bad, or other such anomaly.

RBob.