I have got a slight issue with my GTV and I wonder if you could check my logic?
It is a 1999 3.0 V6 with climate control and a single fan. Apologies for the length of this postÖ
I have recently developed an intermittent slight overheating issue (only in traffic) and I suspect that the fan is sometimes not coming on at low speed when it should.
I donít think it is the radiator because it easily cools the car when it is moving or when the fan does come on. It is also fairly new and still looks in perfect condition. For the same reasons I have ruled out a leaky head gasket, thermostat or water pump.
1. Iíve never been 100% certain about the marks on the temperature gauge. I think that the lower mystery mark is 80 degrees and the upper is 100 degrees?
When moving, it normally hovers a millimetre or so below 90, which I have assumed is about 88? In traffic it moves up to 90 and the fan appears to come in at about 92/half the needle width above 90. The fan used to come on for about 5 seconds and that would move the needle back to 90. Recently however, the needle has been moving up to about 97/98 before the fan cuts in but it only cycles it back to about 95. Once clear of the traffic, it drops back to about 88.
2. Iím assuming that it is somehow skipping the first fan speed, the temperature reaches the threshold for high speed fan but that cuts out once the temperature is low enough for it to expect the low speed fan to take over?
I eventually managed to find what I think is the right wiring diagram by comparing all the likely candidates with the wiring actually in my car.
3. As far as I can make out,
ē The fan has a permanent 12V supply direct from the battery, via a 50amp maxi fuse
ē For low speed operation, the circuit is completed when relay I99 is energised which allows an earth via pin 87 to the ground G53a
ē To stop the fan coming on at full speed, this circuit first goes through a resistor - O22
ē When relay I100 is energised, the fan finds an earth via pin 30 to the ground G53b. There is no resistor in this circuit so the fan spins at full speed (the brown wire to this relay is much thicker as well).
ē The relays are triggered by signals sent from S11, the motronic control unit Ė via the black and white wire to pin 85 for I99 and via the white and red wire to pin 86 for I100
I have 12v to the maxi fuse, the fuse is intact, I have 12v to the fan and 12v at the brown wire connecting to the resistor. So far so good.
4. I donít think the resistor is the problem. It doesnít look burnt out to me; it has continuity and has some resistance (admittedly 0.9 ohms rather than the .23 ohms stamped on the back). Just as a test, I bypassed the resistor by bridging between the two wires but it didnít change anything so I have now put the resistor back.
5. Next step was to look at relay I99. I found this to the right, and slightly in front of the fusebox and identified it because it had a yellow base and had a black, red, white with blue trace and light blue/white wires leading to it. Have I got the right one? I was expecting this to be 30 amp but it is 40amp. It also has five terminals whereas I100 only has four. The markings on I99 are Bitrum 12V 40A, Bo 47, Pa66Gf30. The markings on I100 are TRW Sipea 12V 50A 179. Even if I99 is not the original relay, it still appears to work Ė it clicks when I put 12V across 85 and 86 and I then get continuity across 87 and 30. Assuming I have found the right relay, could the fact that it is 40amp rather than 30 amp be the problem? I donít know when it was put in but Iíve had the car for 5 years and it worked properly until recently.
6. I have 12V at the brown wire to the resistor so, tracing the wiring diagram, should I also have 12V at the light blue and white wire connecting to terminal 30 of I99? I havenít checked yet, but if I should have but havenít, I presume the next step will be to find and check connector G314? Does anyone know where it is?
7. Assuming all the above checks out, I assume that Iíll next need to check if I99 is getting a signal from S11 (control unit) when it gets hot? Is this just a case of running the engine up to temperature and checking for 12V at the white/black wire which connects to pin 85?
8. Is this the contol unit S11? It looks like the signal to relay I99 comes from pin 3. If needs be, how do I check the output of this pin? I presume the engine wonít run with it disconnected?
9. Am I right to assume that it is not worth looking at the min/max pressure switch (trionic switch?) Q20 because this will only put the fans on when the climate control needs it rather than when the coolant gets too hot?
Thanks for any help you can give me. Even if I canít ultimately fix it myself, Iíd really, really like to understand it!