04 GP electrical problem Intermittent no start

[polarisxcr]

My 2004 Grand Prix has a intermittent start no start condition. If I turn the key on and the radio and dash work it will not start or even turn over. Most times when trying to start it the only light that turns on is the check engine light. Some times I have to turn the key off and then to the start position a dozen times before the starter will engage. Then it runs normal and can be driven but the entire dash does not work except for the check engine light. At this time the radio and information display do not work either. Everything else works as it should. I cleaned the battery connections and installed a new battery. I also tried a new Ignition switch. Checked all my fuses and they seem to be good. Cleaned the ground below the battery and the two on transmission. I can always get it started but it would be nice If I could tell how fast I am going. Maybe try bcm next. Any one else had this problem?

[Tech II]

Have it scanned for ALL codes......P,B, C, and U codes.....only a garage with a top of the line scanner can do this....

[polarisxcr]

There is no communication with any of the computers on the car. Tried to scan it when dash and radio were working and then with it running with no dash or radio. Also tried a different bcm today. No change except it would not start. Dash and radio would only come on 1 in 12-15 tries at starting it. It never turned the engine over. The key would not program to it. I put my bcm into the car the borrowed bcm came from. After programing the key it started and everything worked. Is there some other computer or control box for the ignition system?

[Tech II]

Chances are you have a serial data problem, or one of the modules is taking down the whole system.....

If a module loses power, or ground, or the serial data line, it shuts down, and can shut down other modules....if the problem is the serial data line, that will take a lot of digging to find either a break in the line or where a line is grounded(something as simple as a wire harness rubbing against a screw, can cause this).......

I remember a couple places where rub through problems happened on Grand Prix's....one is at the studs where the tranny is held to the engine block on the driver's side.....a harness goes by these studs, and could rub through...

The other problem area is in the lower left front of the engine compartment.....there is a harness that goes by the A/C acumulator, and it can rub though over time on the accumulator.......check both harnesses for rub though conditions....

One other possibility.....I can't remember if the PCM is located in the air box(where the air filter is)...if it is remove the filter and take the box apart....you may find a mouse nest in there and they have eaten the insulation off the wiring harness to the PCM.....

[polarisxcr]

I think it might be the abs computer. Tried switching the power distribution center, then the computer in the air box. No change. Could not find anywhere in the wiring that looked bad. I unplugged the abs computer. Turned the key on and the dash and the radio came on. Turned ignition to start and it fired up and ran great. It starts every time now and everything works. Now the abs, traction , and brake lights are on. Unfortunately the parts loaner car does not have abs so no abs computer to try. Sending mine in to get rebuilt I will let you know if that fixes it.

[Tech II]

Good find......fortunately, there are only a few modules on this vehicle( not like a caddy that can easily have more than 10).......If a module loses power, ground, or serial data or is bad itself, it can take down the system.....

[polarisxcr]

Problem solved. Purchased a used abs computer-pump assembly for $50. Swapped the computer only. Starts every time and the dash and radio work.