The fans on my 96 impala are not working at all. I have changed the relays, temp sensor, fuses and still nothing. I have sent power to both fans individually and I can ensure they work however when I let the vehicle run it will get hot and the fans never turn on. I need help. I have put multiple scanners on this vehicle and don't have any error codes, so I am lost. I believe it's a wiring issue somewhere, but I am stuck.
Fan not working
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Search, Fan TSB on the forum up top you’ll find a lot of great/helpful info.
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The most basic test is to unplug the PCM's temperature sensor at the water pump. When unplugged the PCM turns on the fans because it knows it has no temperature information.
The live data will show what the temperature sensor is reporting to the PCM. I am not sure but I expect the 1996 will also report if it turns on each fan.
If unplugging the temp sensor does not start the fans then you will have to test the wiring. At the relays you can test to see if the PCM is supplying a negative (ground) to each relay. The relay is also the place to check for positive voltage that supplies each relay coil and the positive power for each fan. The relay's control contacts can be "jumped" (bypassed/bridged/shorted) to run the fans.
With four separate fused circuits the fan's have a lot of redundant circuitry. The common ground by the right headlight (on a 1994) would be one thing that would cause problems with both fans.
The circuit diagram:
Relays and fuses can be tested. It is a waste of time and money to replace parts that have not shown any malfunction.
Testing wiring this old can be a challenge as a voltmeter may show volts when something in the circuit is corroded and can not supply the amps to power up something.
Do some testing or get some one to do tests. Then come back and ask questions.
You need to look at live data not for error codes.
The live data will show what the temperature sensor is reporting to the PCM. I am not sure but I expect the 1996 will also report if it turns on each fan.
If unplugging the temp sensor does not start the fans then you will have to test the wiring. At the relays you can test to see if the PCM is supplying a negative (ground) to each relay. The relay is also the place to check for positive voltage that supplies each relay coil and the positive power for each fan. The relay's control contacts can be "jumped" (bypassed/bridged/shorted) to run the fans.
With four separate fused circuits the fan's have a lot of redundant circuitry. The common ground by the right headlight (on a 1994) would be one thing that would cause problems with both fans.
The circuit diagram:
Relays and fuses can be tested. It is a waste of time and money to replace parts that have not shown any malfunction.
Testing wiring this old can be a challenge as a voltmeter may show volts when something in the circuit is corroded and can not supply the amps to power up something.
Do some testing or get some one to do tests. Then come back and ask questions.
OP
as mentioned, unplug the connector on temp sensor on water pump and start car. In a minute the fans should start running. If they do not they are not getting power. Even though relays were replaced.....was the plastic base in underhood relay melted around pins?. There was a TSB addressing this issue. If that is the case get the external fan relay kit from Gary at Innovative Wiring
as mentioned, unplug the connector on temp sensor on water pump and start car. In a minute the fans should start running. If they do not they are not getting power. Even though relays were replaced.....was the plastic base in underhood relay melted around pins?. There was a TSB addressing this issue. If that is the case get the external fan relay kit from Gary at Innovative Wiring
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Define "hot". These cars (in stock form) are notorious for high temps before fan turn-on.
This is exacerbated by the fact that the gauge is tied into a (different) sensor in the head. And the PCM is tied into the sensor in the water pump. They see different readings. You really do want the gauge sensor in the head so you can visualize an overheat condition sooner than the waterpump will see (a head will overheat instantly with poor coolant flow). Whereas the PCM sees more normalized readings at the water pump and will control engine parameters without overreacting to things like hard pulls or hill climbs.
First do what was suggested. Unplug the temp sensor on the WP and wait a minute. If the fans turn on, then it's under control of the PCM. Your gauge may be off in this case. I would purchase a cheap IR temp gun and shoot the thermostat housing when you think it's running hot and verify temps. (FWIW, 220 degrees is "normal" for a B-Body)
When you used "multiple scanners" -- what were they reading as the coolant temp?
If you determine the gauge isn't reading correctly, this is common. The needle moves on the shaft and they go out of calibration. It's also fairly easy to fix. I did a YouTube series about this and plan to do some followups.
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3,101 Posts
GM's OE fan-on thresholds are the problem. The solution is to reprogram the pcm.
If coolant flow is ever compromised, it is entirely possible for the dash temp gauge needle to indicate overheat while the H2Opump temp sensor merely indicates 221F.
That's why the dash temp gauge needle is so important.
(Note that Fleetwoods lack such a gauge, and the OE overheat warnings may be too late ...)
It's important to note that if the dash temp gauge needle is 'off', it may be UNDER-reporting, which is potentially dangerous.
(Obviously OVER-reporting is better, and accurate reporting is best.)
This assumes the H2Opump is working properly, coolant flow is normal, radiator fans work well, and coolant is not chemically compromised.
Again, with GM's OE fan-on thresholds, yes this is 'normal'.
However, it is not necessary for any LT1 to operate normally and ever reach 221F.
Re-read the above. A pcm tune not only improves performance, it also gives peace of mind.
The H2Opump temp sensor readings should be compared to the dash temp gauge needle indications, especially if one wants to learn about how a 30 year old LT1 cooling system behaves.
These are eagerly awaited ...
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