mRahmani

I know I'm bringing a topic back from the dead here, but it's the most relevant one I can find.

I'm getting the same 3 error codes - P0412, P1641, P1642. AIR pump recall was done back in 2001, and the #7 fuse is working fine. Is there any other relay or connection I can start looking at that might tie these together?

Injuneer

What year is your car? Assuming it's a 96 or 97 since you posted in LT1 based engine tech. Below is based on the 1996 factory manual.

P0412 indicates the state of the AIR pump control circuit does not match the state commanded by the PCM. This could be due to the failure of the 12V supplied by fuse 7, including the orange wire between the fuse and the AIR pump relay. Or it could be a failure of the AIR pump relay. Or it could be ground supplied to the AIR pump relay on the brown wire from pin C1-14 of the PCM to the relay.

P1641 and P1642 set when the PCM detects a mismatch on the commanded fan relay control circuits. All the issues described above could apply to this circuit. But since there are four separate relays (3 for the fans, 1 for the AIR pump), and separate ground circutes from the PCM, the only common element is the supply of 12V from fuse #7.

You need to verify that you have 12V at the coil side of each of the relays, with the ignition switch in "run". If you don't have 12V, you have to work your way back on the wiring toward fuse #7. How did you determine that fuse #7 is "working fine"?

mRahmani

Hey, thanks for the awesome info.

The car is a 97 Z28, stock powertrain and factory tune (no AIR delete etc.) When I say the fuse is working fine, I just mean that it wasn't visibly blown, and replacing it with a new fuse didn't fix anything. I'm pretty new to vehicle electrical systems, but I know my way around a multimeter.

Checking the voltage across the fuse itself, I came up with about +2.5V. I'm not sure how to check the relays, though. They have 5 prongs - how do I know which leads to check for +12V?

Injuneer

Voltage drop across the fuse, particularly with neither the AIR pump or the fans running should be near "0" VDC.

The best way to check a fuse with a multi-meter is to measure the resistance with the low ohms scale, with the fuse out of the box. Resistance should be near "0".

In all cases, the 12V DC control wire from fuse #7 to the relays is orange.

One potential problem with the realays - if they are failing, they may work fine for about 2 minutes, then the heat generated by the coil in the relay can short to ground or fail open. But you would have to have all the relays doing that at the same time, and that is not likely.

mRahmani

Finally had some time to work on this, here's what I came up with:

- 0 ohms resistance across fuse #7, also tried tossing in a new one. No change.
- +12V from the right side of the fuse lead to ground. (red wire, goes to fusible links by the battery)
- Left fan comes on low if I pull relay #1 and jump it with a wire, fans come on high if I do the same to relay #2. Jumping relay #3 didn't do anything.
- Tried replacing all 4 relays - cooling fans 1-3. and the AIR relay. No difference.

Any ideas where I go from here?

Injuneer

Did you verify you still have the codes, and that they are not stored from the previous event?

Did you actually measure for 12V on the orange wire terminal at each relay? While you may have 12V on the orange wire at fuse #7, there is a splice (S177) where all four relay wires (3 fan, 1 AIR) attach to the single orange wire from the fuse. If that splice is bad, or the single wire is bad between fuse #7 and the splice, none of the relays will work, and you will get the three codes.

Which pins did you jump on the relays to get the fans to work? You should be testing the signal side (orange wire) of relay only, because that's the only circuit the PCM can see. If you jumped the red wire from the fusible link to the light blue wire on relay #1, you were bypassing the relay completely, and hooking the fan up directly to the battery. Ditto, if you connected the red wire to white wire on relay #2.

GaryDoug

Since you may not be able to see which pin has the orange wires, see if there are markings in the panel under the relays. The ones you want to measure are D5, F5, and J5 for the fan relays, and E5 for the AIR pump relay.

mRahmani

Still testing stuff out on the car. Cleared the codes and they came back immediately. You were right, I was jumping the wrong pins on the relays to make the fans come on.

I checked the resistance from the orange wire on fuse 7 to the orange pin on each of the 4 relays last night, and came up with something like 30 ohms on each, which seems crazy high. Maybe I had the multimeter set to the wrong setting. I'll check for 12V from each when I get home tonight.

Thanks for the suggestions guys!