Check Engine Light is On

I own a 2002 Volvo S80. The check engine light came on a couple months ago during a cold spell. After a few weeks, the light went off. When the light came on again 2 weeks later, I took the car in to be serviced. Our mechanic said the cooling system and thermostat was bad. After spending $700 in repairs the check engine light was off. A couple weeks later the check engine light came on again. I took the car back to the mechanic. They hooked the car up to the diagnostic system and everything checked out fine. They couldn’t find a problem. I paid $180 for this diagnosis and to turn the check engine light off. Now, two weeks later, the check engine light is on again. What could be the problem. My mechanic can’t find anything wrong with the car. Is it safe to drive? I’m at my wits end and don’t want to pay another dime towards the car. I’ve put enough money into it over the years. Please help!

When that light comes on it means that a “diagnostic trouble code” (DTC) has been stored in the computer’s memory. No one can tell you a thing without knowing the codes that were set with the light.

Ask your mechanic what the original code was or check your invoice in the chance that it was written down. Also look to see what kinds of diagnostic steps were taken, if any.

Do the same for the current light, including diagnostic steps.

If you can’t get the codes from the invoice or mechanic, many national chain auto parts stores (e.g. Autozone) read them for free. Have the car scanned, write down the exact code(s) (format: P1234) and post it/them.

The first time I took the car in, on Jan 26th, DTC PO178 displayed. The invoice states the following: Thermostat below threshold system code for electronic coolant sensor in-operative internal fault with sensor. Advised customer replaced thermostat and ECT sensor. Cleared codes recheck system ok at time of inspection and no other codes.

The second time I took the car in, on Feb 19th, the DTC’s that displayed were 431 D Leak Diag, CEM DF416, CEM DF13, AUM-41FF, DCM-0031, BCM 0041, CEM 2E03. The invoice is noted as follows: Perform battery discharge service cleared codes brought sytem back up road test vehicle ok at this time. No fault codes came back. The mechanic explained the codes that displayed were indicative that major parts in the car had failed but, if that was true, the car wouldn’t even run. At that point, they were not able to determine what the actual problem was. Clearly there is something wrong. Could it be an electrical problem? On my way home from work tonight, while in bumper to bumper traffic, I thought I noticed the lights on the dash dimming then brightening then dimming again. By the way, did I mention it has 127,000 miles on it and we spend approx. $2,000 to $3,000 a year on regular maintenance and repairs.

The codes you posted are not standard or Volvo specific codes (OBD-2 trouble codes). They may be some proprietary Volvo diagnostic codes that are derived from Voodoo and Magic. Just for the fun of it, have a parts store read the codes for free and post them back here. They will be in the standard P1234 format…

The CEL is not a safety warning system. It’s primarily an emissions warning system.

In the future, if you wish to minimize your transportation expense, stay away from strange or unique cars that have a long reputation of providing the exact opposite…

While you’re at the auto parts store getting the trouble codes scanned, also, have the battery and alternator checked at curb-side (also, free).

Your first code P0178 Was handled correctly. The car is looking at the engine temperature to make sure it warms up to a certain temp in a certain time determined by the manufacturer. When it fails, it will set the code, and is usually the thermostat.
The second set of codes are in Volvo programming language (not voodoo). Unfortunately disconnecting the battery and preforming a discharge is NEVER the correct way to erase the codes. A 431D code for Leak Diag relates to your EVAP system, also known as your charcoal canister. The most common cause of this code is a loose gas cap, or fueling the car while it was running. It can also be a variety of things most easily diagnosed by a good mechanic with a smoke machine.

Thanks to everyone for the advice. I called AutoZone and learned they only perform free diagnostics for batteries and alternators. They suggested I contact Pep Boys or AAMCO.

I called AAMCO in San Ramon, CA and they told me to bring the car over and they would read the check engine light code/s free of charge. The code that appeared was P1024 related to the emissions. They checked the gas cap which had several cracks in the seal. They suggested buying a new gas cap from a Volvo dealer, then bring it back and they would rerun the diagnostic. I bought the gas cap, took it back to AAMCO and they replaced the gas cap and reran the diagnostic. The code cleared.

The total cost was $29.00 for the gas cap. AAMCO’s time was free. They were wonderful. While I was there, I learned they perform all repairs, not just transmissions. The only thing they don’t do is tires. I’m going to start taking my car there in the future.

AAMCO Reborn…

Yeah, Autozone & other parts stores in Calif. went from pulling the codes to loaning the scanners so the owner could pull the codes themselves & now they do neither.