ok so i bought a new temp sensor for the ECU at autozone. i put the new sensor in and still had the same problem :( then i checked the voltage on it and got 5.1V (cold) then i heated the engine to normal temp and got the same voltage. whats going on here? could they have sold me the wrong sensor? maybe could it be the sensor for the guage on the dash? i'm lost here.


thanks for all your help!

-sal

If it's the '89GL, it should have LH2.4; there are 2 elements in the sensor, both grounded at one end. In Bosch parts, it's got a black insulator.
The LH2.2 sensor (blue insulator) has only one element, not grounded.

The wiring diagram I have for 89 shows the coolant temperature sensor as having two wires connected to it, one white, to the main ECU, one red to the idle stabilizer control unit. Neither one goes directly to ground, unless it grounds internally, through the body of the sensor itself.

The sensor on the 90 engine sitting in my shed has a black insulator, but only two terminals on it.

Hi Blue Horse,

Both ECT sensors have two terminals. The Blue Horse sensor is for LH2.0, and LH2.2. Its one thermistor is connected across the two terminals, so one has to be grounded externally.

The Black Horse sensor is for LH2.4, which we infer is the car in question. It has two thermistors identical to the one in the Blue Horse sensor, but referenced between the brass housing or body and each of the two terminals, so the ECU and the ICU can each have their own independent temperature reference.

A reading of 5V at the sensor connector would lead me to suspect the plug was not fully seated or the pin damaged, or otherwise the circuit is open. It could also be that the sensor in question is the Blue Horse sensor instead of the required Black Horse sensor. The reading should be more like 2.7V when cold and close to 100mV fully warmed, regardless of which (Blue or Black) Horse sense is being used in its proper place.
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Art Benstein near Baltimore

Nobody will ever win the battle of the sexes. There's too much fraternizing with the enemy.

The ~5 volts is reference voltage from the ECU. The voltage and current on the incoming wire to the ECU does change as the sensor resistance changes with temperature, and this how the ECU infers engine temperature.

As Blue Horse says, check the sensor resistance. Easy to do with the sensor out of the engine. Connect the sensor terminals to your multimeter leads and use the ohm (Resistance) scale. Immerse the business end of the sensor (NOT the terminals) in a pot of cool water. Resistance should be something like 2000 ohms. Heat until it starts to boil; resistance should be around 200 ohms. If so, sensor is good. For fun, check your old one, too, and see if it really was the problem. If either sensor is good, check wiring connections.
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Bob (son's 81-244GL B21F/M46, dtr's 83-244DL B23F/M46, my 94-944 B230FD and 89 745 (LT-1 V8); hobbycar 77 MGB, and a few old motorcycles)

Couldn't you just use a lighter?

-Will
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1990 740 Turbo, on its way to stock specs, maybe beyond

Check the resistance of the sensor (ohms) across the two terminals, at various temperatures. The volts are supposed to stay the same at all times. The ECU reads how easily those volts escape through the sensor as the resistance changes. That's how it knows what the engine temperature is.

o ok now i see how it really works. thanks guys, i'll check the resistance tomrrow and let you know what happens.

thanks again

Check the connector itself. I chased a problem where one of the pins in the connector had backed itself out. Easy fix, pull the rubber boot back, and with a jewelers size screwdriver you can remove the one pin, bend the holding tabs back out and re-insert. This applies to lots of the connectors under the hood.
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Post Back. That's whats makes this forum work.