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Old 07-18-2009, 06:28 AM   #1
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Default fan not coming on - need seperate circuit

I'm running the stock ecu and I noticed that my fan doesn't work.
When I ground 1R (R/G) at the ECU, the fan comes on, so that entire circuit is ok.




My temp sensor is giving me about 1K at 25C and 100ohm when the car has been driven (temp gauge at 12), so the sensor is OK.

I checked continuity on the wires from the temp sensor to the ECU (B/R in 3F and R/L in 2E) suggesting that circuit is fine as well.
I checked B/R and it's a good ground.

So, if the fan still doesn't come on, I can only assume that the ecu is faulty? Or could there still be something else?

I shorted 2E to 3F and the fan still didn't come in. Shouldn't 0 ohm immediately turn the fan on?

Assuming my ecu is indeed faulty, can anyone point me to a circuit I can use? I'd hook it up to the stock sensor so that at x ohm, the fan turns on (with some hysteresis in the circuit).
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Old 07-18-2009, 11:15 AM   #2
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Quote:
Originally Posted by f_devocht View Post
I shorted 2E to 3F and the fan still didn't come in. Shouldn't 0 ohm immediately turn the fan on?
Depends on how the programmers decided to handle that case, which I don't know. On the MS, we treat 0v (or 5v) on a sensor input as a fault condition and default that input to some "safe" value.



Quote:
Assuming my ecu is indeed faulty, can anyone point me to a circuit I can use? I'd hook it up to the stock sensor so that at x ohm, the fan turns on
Actually, it'd be "x volts" not "x ohms" as we presume that the ECU is already pulling up the sensor. Which brings us to a good testing point: if you measure voltage between 2E and GND with the engine on, what do you get?


Here's one device that will do the job: eLabtronics Voltage Switch - Prebuilt: 22876 AutoSpeed


No codes?
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Old 07-19-2009, 07:56 AM   #3
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I measure about 2.8V with the engine warm. The thermosensor was about 100 ohm.

The thing is that I have a euro 99 ecu and the pinouts for the ecu are not entirely identical to the US ecu's. For instance, the fuel pump is on an other pin (see the thread Frank's failure). So there might be some obscure pin that needs a signal somehow for the fan to come on (I stripped pretty much everything out - no a/c, no PS, no Power brakes, no electric stuff etc).

I'll order one of those voltage switches if I can't get it going. Thx Joe!
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