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Pontiac Grand Prix engine fault code
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claymor
New User
Jul 16, 2006, 10:15 PM
Post #1 of 1
(4964 views)
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Pontiac Grand Prix engine fault code
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I have a detailed description of the problem and what I have done to correct it. My questions are at the end of this email.
I have a 1999 Pontiac Grand Prix, 3.8 L, V6, Automatic, A/C with 133,000 miles on it.
The problem I have has to do with a radiator cooling fan #2. The temperature gauge on the instrument cluster typically indicates 170-180 degrees. On hotter days it can reach 210 degrees. This operation is very consistent.
All functions on the car work perfectly with the following exception:
I washed my car one evening, including hosing down the engine compartment. The next morning my “Service Engine Soon” light came on. The trouble code is “P0481 – Cooling fan 2 control circuit malfunction”
The owner’s manual said that getting the engine wet could cause spurious trouble codes to pop up but that they will go away after the engine dries out. After a couple of weeks the engine code did go away. Then I drove through a deep puddle of water and the trouble code returned and has continued for over two months. This trouble code is causing my car to fail emissions because here in Seattle, WA they no longer check emissions. Instead, they check your car for trouble codes and if one pops up then you fail.
I looked at the schematic diagrams in the Haynes manual and cooling fans 1 and 2 are operated by the Powertrain Control Module (PCM), pins CI-5 and CI-6. According to the manual, when there is a ground potential on pin CI-6, and no ground potential on pin CI-5, both cooling fan 1 and cooling fan 2 will operate together.
I have noticed that when the fans are operating, it is always both fans that are working. I believe this is determined by whether or not I am using my A/C.
If there is a ground potential on CI-5 and no ground potential on CI-6, then only cooling fan 2 is supposed to operate and cooling fan 1 remains off.
I have never seen cooling fan 2 operate independently of cooling fan 1.
There are two relays, which operate cooling fan 2: “Cool fan relay” and “Cool fan 2 relay”. I have replaced both of these relays and it did not correct the problem. I tested both of the old relays outside of the car and both tested good.
I also removed the cooling fan assembly, cleaned all contacts, and tested both cooling fans outside of the car – both tested good.
I cleaned the contacts of the appropriate fuses, the relays, and the sockets for the relays in the “Fuse Relay Center” and it made no difference. Prior to cleaning any of the contacts listed above, I checked for corrosion and no corrosion of any kind was visible.
According to the schematic diagram, the only two components remaining that might cause this problem are the PCM and the engine coolant sensor. No other sensors would appear to cause this problem.
I believe the engine coolant sensor is located just below the upper radiator hose port on the front-right side of the engine block. That will probably be the next component I replace.
My questions are these:
1) What do you think is wrong?
2) What do you think should be my next step?
3) Does the engine coolant sensor perform double duty in that it operates the temperature gauge on the instrument cluster and provides information for the PCM, or does the engine coolant sensor only provide information for the PCM and the PCM operates the temperature gauge on the instrument cluster? (There are no schematics on the instrument cluster in the Haynes manual so I don’t know)
Any help you can give me would be greatly appreciated!
Thanks,
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