Thread: P0202, P0204, P0300 2004 Grand Prix N/A *Need Help*

I have a 2004 Grand Prix 3.8 N/A with 153,xxx miles.

The car has been running like a great piece of crap with black soot on the rear bumper that has been coming out of the mufflers. Car is throwing P0202, P0204, P0300 codes. Most recently the check engine light has been blinking and I get 6 total codes with all three of those along with the "in progress" codes. I know the codes are injectors 2 and 4 along with random misfire. I ohm tested all 6 injectors and they all came back around 13.3-13.4 after the car running for a few mins, and then after sitting overnight they were all 12.1-12.2.

While I was testing all of those I decided to pull the plugs and wires and replace them as they were factory. Replaced with brand new Delco wires and delco iridium plugs gapped at .060 (both factory). After replacing all of these the car ran the same. (which I didn't expect any differences)

What should be my next step. I was thinking of trying to test voltage at injectors 2 and 4 to see if they are getting the required voltage from the PCM. And possibly just buying another PCM and replacing it as there are a few boneyards within a few miles that have them for $50.

Am I missing anything? Any help would be appreciated.

Yeah. I looked up the codes. I just swapped injectors from cyl 2 and 4 with cyls 1 and 3, cleared the codes and started it up. Codes came on again same ones. So I am to check voltages at injectors next. If voltages are low or erratic a bad PCM or short in the wires is likely correct.

Hmm. Interesting that you say that. I pulled the PCM and the middle harness does have at least 2 wires that the silicon is rubbed off of a little but and some strands of the braid is exposed. Do you have a diagram of those wires to see which ones these wires are?

should i cut out sections and solder in new pieces or push the braids back into the silicon best I can and tape it up?

Thanks for the tips. I'll try that now. Hopefully that is my issue and I won't have to buy a PCM. I'll report back

I replaced the two wires that were frayed. One was green with black stripe, other was blue with black stripe. Both wires corresponded to injector 2 and 4 plugs. (Ohm tested to confirm). Who would have guessed. So I cut, spliced, soldered, & shrink wrapped them. Plugged back in the PCM, replaced the neg battery terminal, cleared the codes, started it up and now I only get a P0300. The P0202 and P0204 is gone.

I still have the P0300 code though. Engine is stumbling like mad. There were two other wires in the same bundle that were melted a little bit but they were not broken or had any braid exposed so I didn't replace those sections. I'm thinking now that I probably should.

Is there any other items that could cause the P0300 besides that?

Yeah, I just double checked.. They are all where they should be.

k. will do. thanks and I'll post back to see whats happening.

I just replaced the 3 other suspect wires. No change. Still have a flashing CEL and P0300.

Well I tested the coils and the wires. All 6 had no issues and showed spark. I just did the plugs along with the wires. There isn't an external fuel filter (its in tank). I'm stumped.