I recently bought a 2004 Commemorative convertible with 36,000 miles. It ran great. I changed oil, oil filter, and air filter last weekend. Drove it for three days, no problems. Last Wednesday...it started and ran fine, stopped at the hardware store, went to restart and...
--"Reduced engine power" and
--Codes
P0101 Mass Air Flow (MAF) Sensor Performance
P0412 Secondary Air Injection System Switching Valve A Circuit Malfunction
P0418 Secondary Air Injection (AIR) Pump Relay Control Circuit
P0443 Evaporative Emission (EVAP) Purge Solenoid Control Circuit
P0645 Air Conditioning (A/C) Clutch Relay Control Circuit
U0107 Lost Communications With Throttle Actuator Control (TAC) Module

I started it three or four times with the "reduced engine power" as a result. I got it to start one more time at full power, but check engine still showing and got it home. It wouldn't start again; thank goodness, I made it to the house. I visually checked the MAF sensor: not bad, but I cleaned it. MAF wiring looked good, although I did not test them. I visually checked the throttle body...nothing obvious. The throttle body did click non-stop when the key was in run position, but the engine was off.

I scheduled a flatbed to pick it up next Wednesday to take to the shop.

A part of the trail: Many of the write-ups I found on the codes stated that a bad battery could cause problems. The guy I bought the car from told me that he had just put a new battery in it...and he had, but I took a look at it. It was the ultimate no-name battery. No name, as in not even a sticker on it. I replaced it with an Optima red top on Thursday. Not only was it a no-name battery, but when I went to remove the negative terminal connector, I found that it was not tight and, in fact, the terminal was just enough too small to keep the connector from being able to tighten up on it. However, even with the new Optima battery, the car still would not start.

Also (and while this sounds extraneous, it's what led me to the problem and the solution), I had ordered a key fob to replace one of the originals. It came in Friday, two days after the car stopped working. I took the fob to the car and paired it and tested the buttons--lock, check; unlock, check; trunk release, check; alarm...no check. Rather, hitting the alarm button elicited only a clicking sound from the relay. I found the relay and pulled another one from the fuse box and switched them. The alarm worked. I tried to start the car again; no joy.

I wondered if the bad battery/bad battery connection had fried the alarm relay, which made me wonder what else it might have fried. I checked all of the fuses, paying particular attention to any fuses that had anything to do with engine management; they were fine. I saw that there was an ignition relay in the engine-area fuse box, so I switched one of the fan relays with the ignition relay and, after three days of "no start", she fired up immediately when I turned the key! I replaced the ignition relay and the alarm relay and all is well. All engine codes cleared and the car runs perfectly. My suspicion is that the lousy, new battery and its inadequate negative terminal connection screwed up those two relays. Out of an abundance of caution, I will replace all of the other relays in both fuse boxes. The new Optima battery and the new fuses will cost about $325 in total, but I feel like I dodged a bullet. Thank goodness I spent the $12 on the new key fob, which led me to find out that the alarm relay was bad.

I just wanted to share this, as it was one of the weirdest rabbit trails I've ever been down and thought it might be helpful. Also, please let me add that I appreciated all of the threads that I read that led me to wonder if the battery might have something to do with the faults the car was showing.

Mojo

 

Great that you finally got it resolved...just looking at the first 4 DTC's it had to be either a power or a ground issue especially when the DTC has the word "circuit" in it...yes, ignition relay 42 feeds those circuits but I'd have to look at the HVAC and TAC Module wiring to see if they also get their power from that relay...good job Mojo !!

 

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