My car has had the p1642 code since october at first it would come on then go off after a while. But it has been solid for over 4 weeks. My fans never had a problem until yesterday. I noticed my car was getting hot, then when I got home my fans were not working. I have searched and it seems that the only things that can cause this is wiring, relays, or the temp sensor. Is there anything else I should look at. Thanks

 

The 1642 (not 1643) is the fan control for relay #2 & #3. They are both on the same line coming from the PCM. FYI, this line like many others is monitored by the PCM. One side of the relay coil is tide to a fuse the other side of the coil goes to the PCM where it activates the relay by grounding the side the PCM is tied to.

So the first thing to check is the 25amp fuse #7 in the UH fuse panel.

Because the relay coil is just a coil of wires, it will allow voltage to pass thru it up to the PCM on the dark blue control wire. It goes to C1, the Red connector at the PCM on pin 10. The PCM monitors this line before it commands the fan (relay) on to be sure it is at 12 volts. If it doesn't see 12 volts, it will set a 1642. When it commands a fan on signal, as I mentioned before, it grounds the dark blue wire to complete the circuit and power the relay.

So what you need to do is be sure voltage is getting to the relay and then up to the PCM. When ever you deal with tracing a circuit, work in halves. Start in the middle and work in the direction toward the source if you don't see the voltage or away from source if you do.

The dark blue control wire from the relays (relays F & J) to the PCM passes thru C100. The black 10 pin connector by the PCM. So you can either go right to a relay socket or C100 (which only has one dark blue wire) to confirm the presence of 12 volts with the key on.

If you pull a relay and measure for the presence of 12 volts, remember there should be 12 volts on 2 of the relay pins when KOEO. If the fuse is good but the relay doesn't have power on the coil pin, trace the orange wire from the relay to the fuse under the fuse panel. On standard relays as used here, the pin configuration is the same. Pins 85 and 86 are for the coil. These are the coil you are concerned with. They are what actuates the relay. The other 3 pins are the contacts for the relay. Just FYI pin 30 is the common. Pin 87 is normally open when the coil is not energized. Pin 87A is normally closed when the relay is not energized. But don't let the FYI confuse you.

The 2 pins that should have power with KOEO are one of the contacts and the one you are concerned with, the one for the coil.

If you check relay F and it has power on only one pin and relay J has no power on any pins, there could be a problem on the orange wire. Or the fuse contacts.

 

oops I mean P1642. I did check for power I have no power on the blue wire at the 10 pin connector, with the key on. I have power on pins 85 and 30 at relay F but only have power at pin 85 on relay J. I also have power on both sides of fuse 7. The fans also do not come on when the ac or heater is on.

 

Both blue wires at the relays also have power. But no power is making it to the blue wire at the 10 pin connector. If I put power to the blue wire at the 10 pin connector I can turn off the SES light, but fans do not run.

 

The dark blue (or dark green) wire at C100 is never supposed to have 12v on it. If you go putting 12v to it, you may fry your PCM. A ground comes out of the PCM to operate the fan relay.

There are fan schematics on my website you can use for troubleshooting.

 

Sorry but the dark blue wire WILL have 12 volts on it until the PCM commands the relay to activate by sinking the line to ground level. That is what a 1642 is, lack of the voltage when the device is not activated. For those that can't see it(remember a coil is just windings of wire) by merely looking at the schematic, reading the shop manual will explain it. This is how the PCM checks for continuity of the control wire. This explains why the PCM cleared the code when you applied 12 volts to the wire. However, don't jump any more directly without some sort of resistance in line. The PCM sinks low current to ground with "drivers" however there needs to be devices inline to limit the current draw.

Your blue wire is obviously broken or not making contact somewhere between the PCM and the relay socket. Your next job is to pull the connector at the PCM and pull the relay and ohm the dark blue wire between the relay socket and the PCM.

Not only is there C100 in the line, there is also a splice between the relay and C100 that branches to the other relay socket. But I can not find where the splice is. It should be easy from here to find the continuity problem of the dark blue wire.

 

I guess I was in too big of a hurry to reply. I was thinking no power with the key off, but that only applies to pre 96s. Sorry for the confusion. Still, jumpering unresisted 12v toward the PCM is not a good idea, as we both agree.

 

Just like my answer for the guy with the happy hooker. I don't know why for the life of me I was thinking Hooker Headers.

Glad to see you are actually human.