QuestionQUESTION: I just rebuilt the motor in a 2002 or cruiser but have a power issue. Inside the car, fuse number 12 pdc Rlys ldp keeps blowing and I don't get a radiator fan and two obd codes. 1490 and 1495z. How can I go about finding the source?
ANSWER: Hi Jeff,
To begin, I believe you mean fuse 12 in fuse box in the cabin is blowing, not 12 in the pdc of the engine compartment, correct?
That fuse powers a number of actuation coils in relays, a pump, and the tcm:
low speed radiator/high speed radiator, ac compressor clutch, as well as the transmission control module, and the leak detection pump proper on the top of the fuel tank. The current leaves the fuse on a light green/black wire and goes to all those components.
The fault codes point toward the low speed radiator fan relay circuit and the leak detection pump circuits more specifically.
So you could see what the resistance to ground is showing at the fuse output pin (the lower pin of the fuse) specifically, which is probably close to a dead short, and then try removing/disconnecting each of the items that I listed above to determine which one when removed causes the resistance to ground reading of the fuse to go up significantly above 0 ohms. Then check the item and its light green/black supply wire to find out what is the source of the "short".
Roland
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QUESTION: What kind of resistance am I looking for? Something above 5 is normal and around 2 is shorted? Also once I isolate the section of wore do I just use continuity to find the source of the short?
ANSWER: Hi Jeff,
The fuse is 10 amp so a resistance of about 1.5 ohms or less will blow it. There are a number of items drawing on the fuse so it might show around 4 ohms and still not blow (for example when the pcm had called for one of the relays to close by grounding one end of the activation coil of the relay). I suspect though that somewhere along the harness carrying the light green/black wire there is an opening in the insulation which is directly shorting the wire to ground and that would give you a reading of less than an ohm. So try gently shaking the harness carrying the wire to find where the resistance jumps up. Also visually inspect the harness for damage.
Roland
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QUESTION: So I am checking it now, with everything plugged in relays and all I had resistance of 75 ohms at the fuse block and ground. When I unplugged radiator fan the resistance dropped to 5 ohms. Removing relays did nothing for resistance levels. Also there are three words going to fan yellow black and green there is not a green with black strip. I did locate that wore under hood going to fuse/relay block there
AnswerHi Jess,
The 75 ohm resistance between the fuse and ground will of course not blow the fuse. I had the impression it was blowing right after you started the engine. I guess not. At what point in the operation does it blow, if you know?
The dark green/black wire goes to the actuation coil of the relays that I listed, not to the devices that the relay operates. So that is where you should look for that wire in all cases.
I don't understand why unplugging the fan should cause the resistance to drop unless so-doing cause the pcm to request the fan to come "on". But in any case that is still too high a resistance to blow fuse 12.
Your fault codes pointed at the low speed radiator fan relay and the leak detection pump circuits as being the source of some malfunction so I would check the dark green black wire to those two devices to see if either has a short.
Roland
