Possible PCM Damage
06-01-2008, 07:21 PM
#1
Staging Lane
Thread Starter
iTrader: (6)
Join Date: Nov 2006
Location: Saint Augustine, Florida
Posts: 84
Likes: 0
Received 0 Likes
on
0 Posts
Possible PCM Damage I blew one of the maxifuses for my fans and now the highs will not turn on. The fuse has been replaced. It is just the highs that do not work. If I ground the relay the fans turn on. I have checked the continuity between the the pcm and ground side of the relay and it is fine, so it is not in the wiring. I also let the car warm up to about 240 and the fans did not come on. So I'm guessing that the PCM is not grounding it. It did throw a P0481 code.
It is also throwing a P0443 which is for the EVAP purge solenoid. I checked the continuity there too and it is good. Both codes came on at the same and both of the control wire pins at the PCM are next to each other at the PCM connector. So I am thinking that something happened inside the PCM. The connections at the PCM are clean and dry. What do you guys think that it is?
It is also throwing a P0443 which is for the EVAP purge solenoid. I checked the continuity there too and it is good. Both codes came on at the same and both of the control wire pins at the PCM are next to each other at the PCM connector. So I am thinking that something happened inside the PCM. The connections at the PCM are clean and dry. What do you guys think that it is?
06-02-2008, 05:04 PM
#3
Have someone with a scanner command the fans on for high speed. Backprobe the fan wire while doing it. Once it is commanded it should ground and the fans turn on if not the the pcm let the factory installed smoke out. The other thing to do is make sure both fans and the according relays are turning on when you ground them and verify with a voltmeter.
06-02-2008, 05:16 PM
#4
Staging Lane
Thread Starter
iTrader: (6)
Join Date: Nov 2006
Location: Saint Augustine, Florida
Posts: 84
Likes: 0
Received 0 Likes
on
0 Posts
All relays are working when I ground them. I let the car heat up to about 240 so the fans should have been on. This is the same as commanding the fans on and there was not a ground at the fuse box where the relay pugs into.
06-02-2008, 05:42 PM
#5
With the pcm unplugged and the key turned on and all of the fuses installed pop the pcm connector pin protector off of the pcm connector with the high speed fan wire. I don't remember which one it is off the top of my head then use a dvom and ground one side and put the other on the high speed fan pin it should read 12 V if it does then this verifies the wiring from the pcm to the relays is fine. The 12v is feeding thru the relay coil and to the pcm, when the pcm commands high speed it grounds and the fans come on. If it does not have 12 v under the above conditions then it is for sure a connection problem from the pcm to the relay box. The code the pcm is setting is because it does not see this 12v signal while the fans are commanded off and the engine running. If the pcm does not see this 12 v signal then it knows it has a circuit problem. You really need a scanner to see for sure if the pcm is actually commanding the fans on. If you do have 12 V signal under the above conditions then the quad driver for the fan output in the pcm failed.
06-02-2008, 07:15 PM
#6
A relay is a low current coil that operates a high current set of contacts. The low current side is controlled by the pcm so I don't see how it could be bad. The high current side has the big fuse and fans.
So the fuse just blew out of nowhere and you changed it?
Since you have no tuning device, I'd pull the relays out and put a jumper wire between the high current (fan circuit) contact terminal slots on all relays. Without the key on, the fans should come on, if they don't it's a problem in the high current wiring or the relay.
I'd bet on the high current wiring since it blew a fuse, probably a wire worn through somewhere.
So the fuse just blew out of nowhere and you changed it?
Since you have no tuning device, I'd pull the relays out and put a jumper wire between the high current (fan circuit) contact terminal slots on all relays. Without the key on, the fans should come on, if they don't it's a problem in the high current wiring or the relay.
I'd bet on the high current wiring since it blew a fuse, probably a wire worn through somewhere.
06-03-2008, 10:43 AM
#7
Staging Lane
Thread Starter
iTrader: (6)
Join Date: Nov 2006
Location: Saint Augustine, Florida
Posts: 84
Likes: 0
Received 0 Likes
on
0 Posts
A relay is a low current coil that operates a high current set of contacts. The low current side is controlled by the pcm so I don't see how it could be bad. The high current side has the big fuse and fans.
So the fuse just blew out of nowhere and you changed it?
Since you have no tuning device, I'd pull the relays out and put a jumper wire between the high current (fan circuit) contact terminal slots on all relays. Without the key on, the fans should come on, if they don't it's a problem in the high current wiring or the relay.
I'd bet on the high current wiring since it blew a fuse, probably a wire worn through somewhere.
So the fuse just blew out of nowhere and you changed it?
Since you have no tuning device, I'd pull the relays out and put a jumper wire between the high current (fan circuit) contact terminal slots on all relays. Without the key on, the fans should come on, if they don't it's a problem in the high current wiring or the relay.
I'd bet on the high current wiring since it blew a fuse, probably a wire worn through somewhere.
The high side works fine. I can do the jumper and it works. If I ground the relay(low current side) the fans come on. The relay is not getting a ground, but the wire between the PCM and ground terminal has continunity.
Trending Topics
06-03-2008, 08:56 PM
#9
I'd change the relays too. It's damn odd to blow the fuse on one circuit and blow the ground on another. If the relay failed somehow it might have crossed the two circuits.
I'd be more tempted to run a manual switch for a while to see if the problem shows up again rather than put a whole new ecm in never finding why it failed.
I'd be more tempted to run a manual switch for a while to see if the problem shows up again rather than put a whole new ecm in never finding why it failed.
06-04-2008, 01:48 AM
#11
Staging Lane
Thread Starter
iTrader: (6)
Join Date: Nov 2006
Location: Saint Augustine, Florida
Posts: 84
Likes: 0
Received 0 Likes
on
0 Posts
I ordered a new PCM, it should be here sometime this week. I do have a manual switch for right now, it gets pretty hot here in Florida, in traffic and the lows were not enough. Thanks for the help and I will let you guys know the outcome.
