myk

iTrader: (4)

Hey guys, another question for you. I'm sure there's a problem with my fans in that they will only turn on if I jump them directly from battery power. All 3 relays test as working and they're good. I consulted shbox.com and saw that if I jumped terminals 5 and 6 on the OBD connector the fans should turn on, but they don't. When I run the A/C I don't think the fans turn on. I'm thinking this is a PCM or wiring problem, but then someone else suggested that the ECT sensor could also be bad. Any ideas? Also, if it IS the ECT, how do I tell the parts store which ECT sensor I need? There's one in the water pump and another in the head for the 'temp gauge, as I understand it. Any input is welcome...

shbox

Please provide car info when asking for help. Yes, the fans should come on when you jump the DLC. That may indicate a PCM problem or with the green and blue control wires from the PCM to the fan relays.

myk

iTrader: (4)

My apologies; '97Z28, all stock.

Now, I feel stupid for suggesting this, but is there a possibility I'm not jumping the DLC properly? I'm cramming a wire between 5 & 6, but I was told that there is a series of events that will happen when you enter field service mode but the car doesn't respond at all. There are no codes, pending or otherwise, and the car is otherwise fully functional...

cardo0

Ya know that happened to me just before my PCM4less tune install. I wonder if i had rebooted the PCM it would reorganize things. To try a full reboot disconnect both batt cables and step on the brakes a bit to discharge anything. Reconnect and start'er up.

Hope this helps.

shbox

I guess it is possible you might not have continuity to ground on pin 5 or continuity to the PCM on pin 6. If either is open, then it won't engage the mode. You'd have to check that out. You won't get any codes this way, but it is unclear that you meant you got none with a scanner.

Go under the hood and unplug C100. On the forward side of the connector, use a jumper to ground and touch the green wire in cavity J. That should enable low speed fans. While still touching J, also touch H (blue) and you should get high speed fans. That will at least tell you if all the circuitry is ok from there to the fans.

myk

iTrader: (4)

I was refering to a scanner not providing any codes.

Ok, so ground terminal J from C100, check for low speed, then simultaneously ground H to check for high speed?

myk

iTrader: (4)

Alright, so I grounded both terminals J and H from C100 on the forward side and got both speeds. So that indicates that all wiring forward of that harness junction is good. So I'm guessing the problem is from the other side of the harness; is there some way I can check to see if a signal is coming from the PCM? BTW, why hasn't a DTC code been set yet? According to my scanner there are none pending, either...

shbox

There are codes for the fan relay circuits, but apparently you are not triggering any. When you ground the DLC into field service mode, you should see a ground on the green and blue wires toward the relays (same thing you were doing with your jumper wire). If you don't see that (and I expect you will not), you might want to make sure there is continuity from C100 back to the PCM connector. You will need to remove the PCM connector and ohm the wires between those points. It is not often that the PCM has an issue like this, but yours may be having one.
Another thing you could try for grins is to cause a DTC (like unplug the ECT at the water pump) and see if the fans come on. This is just in case the DLC jumpering is not working.

myk

iTrader: (4)

I will check for continuity between those points. Question about triggering the DTC: will the fans turn on as soon as I pull the ECT connector, or will the DTC have to trigger the MIL first?

shbox

Those things should be fairly simultaneous.