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    Ford Escort 1600 16V 1998 Alternator/Temp Gauge Fault Archived Message

    Posted by George Georgiou on July 22, 2008, 10:22 am

    I serviced and repaired the AC on this vehicle , switch on dash to turn on AC had failed. Customer went on driving holiday only to find that alternator light came on.

    Garage diagnostics concluded faulty alternator, was replaced with new Bosch unit (plain old alternator, not smart charge). only to find battery light still on , replaced unit again and when customer came to pick up car , bat light still on and was told to rev engine to put it out. After filling up for the return journey at the petrol stattion ,light on again and revving up put it out again. Car drove fine until motorway services (100 mile run) stopped and on re-start found light would not go out on revs and at the same time temp gauge showed permanent hot, even with engine switched off.

    Thats where I came in after car got towed back to customers house. I tested feed wire to field coil and found it to be close to zero volts with engine running , no output to battery. I managed to 'excite' the alternator by touching a +ve battery feed briefly to coil feed wire. Alternator started up and worked fine giving good output voltage and current under all load conditions. At the same time I found removing temp sender plug from temp sender allowed gauge to drop to cold end of gauge and by resitor substitution tested gauge fully from about 100 ohms down to 40 ohms. Next day came back and replaced sensor with Ford part and gauge worked perfectly sitting in the middle with engine fully warmed up. The original sensor was shorted when measured , zero ohms.

    All was well for a week and then customer rang to say car had stalled and could not re-start. He drove it for some time after starting it with the red light on !!! I told him with the blower fan on it would only be a short time before battery would discharge and ECU stop working , hence car stalling. Car pushed back to his house .Next day car started and moved off driveway, so battery had recovered enough to at least start the vehicle.

    My next inspection found that the temp gauge was indeed stuck to the hot (max) again and removing connector caused it to drop to cold (min) reading. Also bat light was on again. Looks like new sensor had failed again , only this time putting resistors to test gauge caused my small resistors to start smoking, due to excessive current draw. I suspect I now have a more premanent fault with the wiring/temp gauge on the dash ???

    Also the moment I removed the connector to the temp gauge sensor the alternator battery light went out and the alternator started to run as normal with very good voltage and current delivery on all loads. NOTE: Prior to removing the temp gauge connector I tested the field wire and found it to be almost zero volts, i.e. no output from alternator to battery light, after I removed temp sensor connector the voltage measure 14 volts approx.and the alternator worked as normal.

    I am susepecting the dashboard as being the centre of this fault as it seems both times the bat light has stayed on has coincided with the temp gauge failing and getting stuck on hot. However when I reconnect the temp sensor wiring to the 'shorted' sensor , the bat light does not come on and the alternator is working fine. Could it be a faulty voltage regulator on the dash causing a problem to the bat light feed? The petrol gauge and all other indicators and speedo are all fine .

    I do not have circuit diagram for the dash so would be grateful if anyone has one to perhaps send me a copy so i can strip down the dash and do some tests.

    I have tested all wiring for voltage drops and cleaned main body earth from battery to ensure no power problems to and from battery to alternator /chassis etc.

    My conclusion is that the temp sensor /temp gauge causes the bat light to come on and stops the alternator from charging . It would seem that this state is permanent until the temp sensor is disconnected or the alternator manualy excited, then all seems to be well.

    I have told customer to drive car and have disconnected temp sensor wiring . I predict bat light will not come on. Car uses the ECT sensor to control fans and cooling so no problem here, but I still need to get temp gauge working for obvious reasons.

    George

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