Where is the temp sensor?

joshwfl · Aug 17, 2010

2000 GT and I have a continuing fan problem. New CCRM tests fine, but the low speed fan never comes on even at operating temp. It does work when wired straight though. I found the sensor for the gauge (top of intake, pass side in crossover tube), when I unplug it the guage falls to cold and the ac kicks off. Is there a separate gauge for the PCM? If not, could the sensor be 1/2 bad giving a good gauge reading, but not triggering the low speed fan?

wmburns · Aug 17, 2010

The 1999+ MY's have only one temperature sensor located in the intake manifold cross over. The temperature sensor output goes directly to the PCM. The PCM makes all of the decisions regarding what to do.

This is where an ODB2 scanner can be very handy. Use it to monitor what temperature the PCM "thinks" it is. There is also a PID for fan speed (off, low-speed, high-speed).

For example, if the PCM is calling for low speed fan, we can test for this at the CCRM. Then it becomes a matter of figuring out if it is a break down in the wiring or in the PCM itself.

Note, your post does not tell HOW the CCRM was tested. These small details can make the difference. Esp when as many things have been tried as in this case.

For example, were the CCRM pins 14 and 17 grounded to test fan operation?

Have you confirmed/tested the low speed aux circuit breaker on the right hand engine compartment? A bad F1.31 Circuit breaker would exactly cause this symptom.

joshwfl · Aug 17, 2010

Help me locate the low speed aux breaker and it'll be the first thing I check after work tomorrow. I want this crap fixed (although it is nice to let the LX see some miles)

wmburns · Aug 17, 2010

Do you know where the battery junction box is? The aux fuse box is located on the right hand fender well directly in front of the strut towers. It lines up exactly opposite of the BJB. It is about 2x4 inches.

joshwfl · Aug 18, 2010

Wondered what that was for, thanks!

joshwfl · Aug 18, 2010

Cb is fine, power on both sides when ac is on max. Nothing with ac off and at operating temp. I'm going to replace the temp sensor even though the gauge reads normal. Hopefully that's the fix.

joshwfl · Aug 18, 2010

No change. The compressor then fan kicks off even when on max. When the fan is wired to direct power, the compressor stays running.

wmburns · Aug 18, 2010

joshwfl said:
Cb is fine, power on both sides when ac is on max. Nothing with ac off and at operating temp.

There a problem!

The CB is for the LS fan. It should only have power when the LS fan is active. When the AC is running, the HS fan should be engaged. No power through the LS circuit.

Check out the attached diagram.

So.....either there is a problem with how the test was performed or this is your problem.

If the test is correct, this means that the low speed relay is engaged all the time, or there is a short in the wiring harness, or the PCM is bad.

joshwfl · Aug 18, 2010

I did a simple test using a test light. With max ac, the cb has power, but at no other time. I've gone through 2 brand new ccrms, guessing I have a short somewhere destroying the ls relay.

Also: When the ls cb has power, the hs fan is running!

wmburns · Aug 18, 2010

joshwfl said:
I did a simple test using a test light. With max ac, the cb has power, but at no other time. I've gone through 2 brand new ccrms, guessing I have a short somewhere destroying the ls relay.

Don't presume that the new CCRM is bad. Consider that if CCRM pin #17 were grounded, this could cause the symptom.

This is not going to be an easy problem to solve. Best to review the wiring diagram so you can see how it works.

This could be something as simple as a solder wisker shorting out adjactent connections. If this were my car, I would first remove the CCRM and clean both sides of the connection.

From here on, this will get messy.

joshwfl · Aug 18, 2010

First thing I did was clean both plugs using CRC. I had to wire the fan to a switch tonight so I can at least drive to work. Time to start tracing, damn I hate electrical problems.

wmburns · Aug 20, 2010

I have been thinking about this problem. IMO, there is a possibility that the test is flawed. What may be happening is that voltage is feeding backwards through the High speed circuit of the fan itself. When +12 volts is measured on both sides of the CB, it is coming FROM the fan but no current is actually flowing.

The test needs to be repeated with the CB removed. This will isolate the Low speed fan power source from the fan itself. Now test for +12 volts on Pin #1 of the CB. If there is voltage now, it is coming from the CCRM. To confirm, test for +12 volts on CB pin#2. If present, this is coming from the fan.

Sorry about the false lead.

As mentioned previously, this sort of electrical problem could turn very ugly. I believe it can be solved but it may take some very detailed tests.

joshwfl · Aug 20, 2010

Makes 100% sense. I'll try that tonight. For now, the fan is on a switch. The ac isn't as cold now with the fan switched. All these symptoms reared up after having the compressor replaced a few weeks ago. That lasted 3 days before the compressor coil went, then the fan problem started.

Wish this would have happened while I was on vacation for 2 months, just started back to work this week.

wmburns · Aug 20, 2010

Let's fall back and re-group.

-Car harness tests:
Disconnect the fan connector. Measure the resistance between the BK wire and battery negative (key off). Post the results.

With the fan connector still disconnected, start the car and run the AC. Probe the RD/OG and OG/LB wires for +12 volts. Post the results.

-fan tests:
Towards the fan. Confirm the low speed fan runs when powered directly via the RD/OG wire.

Next power the OG/LB wires. The high speed fan should run. There should be an obvious difference in fan speed.

These tests are to confirm that the fan has been wired correctly (HS and LS fan not reversed).

joshwfl · Aug 21, 2010

wmburns said:
-Car harness tests:
Disconnect the fan connector. Measure the resistance between the BK wire and battery negative (key off). 0

With the fan connector still disconnected, start the car and run the AC. Probe the RD/OG and OG/LB wires for +12 volts. Post the results.
With max ac on, HS fan comes on.
RD/OG has power, OG/LB has power

-fan tests:
Towards the fan. Confirm the low speed fan runs when powered directly via the RD/OG wire.
LS runs when powered direct

Next power the OG/LB wires. The high speed fan should run. There should be an obvious difference in fan speed.
HS runs when powered direct

These tests are to confirm that the fan has been wired correctly (HS and LS fan not reversed).

As far as the CB: When fan is wired direct with ac on, pass. fender side of cb has power

With the fan plugged in and max ac on:
HS fan runs and power on pass. fender side of CB
If I unplug the CB, fan and compressor kick off and stay off even after replacing CB

With ac off the fan did kick on and off a few times, usually running for 30-45 seconds. It did feel like the high speed fan running though.

With the fan plugged in, everything seemed to work fine until giving throttle which kicked the ac and fan off. The ac would come on and off after this, but the fan stayed off.

What seems strange still:
1- When the fan came on at operating temp, it felt like HS
2- When the fan is wired direct either HS or LS, the opposite terminal also
has power
3- When the fan is plugged in with ac on the compressor and fan shut off upon throttle. When the fan is wired direct with ac on, the compressor won't kick off.

wmburns · Aug 21, 2010

Here's my theory. The Low speed fan is engaged all the time. This is powering the HS and LS at the same time. Because the same voltage is present on BOTH fan terminals, this effectivly bypasses some/most of the fan coil. This has the effect of making the fan run on a lower speed.

Take out the low speed circuit breaker from the aux breaker box. This will have the effect of temporally disabling the LS fan. The LS fan will not run, but as the motor warms up, the HS fan will kick on. It should also work normally with the AC on.

Drive it for a while and see if it works better/same as the direct wire. This will PROVE the theory.

Once the theory is proved, we can work on WHY the low speed fan is engaged all the time.

joshwfl · Aug 21, 2010

With the CB removed, the hs fan doesn't run with the ac on.

By the way, thanks for the help thus far. I really do appreciate it!

wmburns · Aug 21, 2010

Go back and look at the diagram. It is clear that the Low speed CB controls the low speed fan. With the CB removed, there is no way for the LS fan to run.

Therefore, if the fan quits completely with the Low Speed CB removed, this says that the High Speed fan is not functioning at all. What you have been hearing run all along was the Low Speed fan. This would also explain why the car is over heating.

Previous posts stated there was power in the car's fan harness for both the LS and HS speed terminals. Further, you confirmed that the ground return resistance is zero (IMO this is some what of a doubtful measurement. I would have expected a very low reading such as 0.25 Ohm).

This tells me there is an error somewhere. I want to caution you to be careful as these tests are performed. A wrong result could send us both (more yourself) on a wild goose chase.

Go back and look at the fan connector itself. Check for loose, dirty, overheated terminals. The fan carries a lot of current. To carry the heavy load, the terminals must be in good condition.

Repeat the tests. Double confirm the results. Otherwise, get the "chill pills" ready. You may need them.

joshwfl · Aug 21, 2010

wmburns said:
you confirmed that the ground return resistance is zero (IMO this is some what of a doubtful measurement. I would have expected a very low reading such as 0.25 Ohm).

This tells me there is an error somewhere. I want to caution you to be careful as these tests are performed. A wrong result could send us both (more yourself) on a wild goose chase.

Go back and look at the fan connector itself. Check for loose, dirty, overheated terminals. The fan carries a lot of current. To carry the heavy load, the terminals must be in good condition.

Repeat the tests. Double confirm the results. Otherwise, get the "chill pills" ready. You may need them.

My digital meter wasn't working properly, so I had to use an older needle type. When testing the resistance, the needle dropped right to zero. Should've stated that's why it was a "zero" reading.

As far as the fan running with the cb in, it's definitely the high speed. After all the testing I've been doing I can tell the difference now between the amount of air moved and the sound difference between hs and ls.

The fan blade connectors are tight, I cleaned them with a folded piece of sandpaper, and there's no sign of overheating or melting on the wires or plug itself.

I'll check the diagram and pick up a new digital meter tomorrow and retest. Thanks again for the continued help!

wmburns · Aug 21, 2010

An analog meter should work just fine. What setting did you use (should be a low multiplier).

Remember I said there has to be an error. Well it may be me. I repeated the tests on my 2000 GT. When the LS CB is removed with the AC on, the fan stops working alltogether. After about 30 seconds, the High speed fan comes on. The HS fan runs for a few seconds and then shuts off completely. The cycle repeats.

This tells me that some assumptions are incorrect. There may be some logic in the CCRM that makes the fan run for fail safe reasons. I do have an ODB2 scanner. I will run some tests and compare the results. Maybe come back smarter than I was yesterday.

Where is the temp sensor?

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