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I have a 2003 PT Cruiser. Can a bad pcm cause other engine error codes? I've had CEL codes p0303 & p0072 for some time. My car shows all the symptoms of a bad pcm.
Hello and welcome to JustAnswer!
What have you done to try to correct the problem?
I've taken the car to the dealer numerous times for diagnosis. new spark plugs, new battery this year
Has anything been replaced besides the spark plugs and battery?
How does the miss feel? Is it like a dead cylinder, random misfire?
I haven't had the money for regular maintenance other than oil changes, just the serious stuff. Sometimes the car run great - most of the time there is a very rough idle, especially at stop lights and when the vehicle is first started. I never use the a/c or heater - makes the problem worse. If the engine light happens to be off, the ac & heater will cause the light to come back on. Slow acceleration with "hesitations" & "jerks" around 45 - 55mph. The engine light flashes when this occurs.
Ok. If the light is flashing that is a severe misfire that could be causing damage to the catalytic converter. If the plugs have been replaced they should be ok, but they might have been damaged again. A common cause of a misfire in these is flashover. This is when spark takes a path along the outside of the spark plug porcelain and fires to the head. This ruins both the plug and the wire. This is more common than a bad spark plug in these. If your wires haven't been replaced that is definintely what needs to be done next. The bad wires can ruin a brand new set of spark plugs too. if the porcelain on the plugs have black streaks on them it's because the spark has eroded away at them. They would need to be replaced again.
you've touched on another problem that isn't uncommon. With the a/c or defrost on the a/c cooling fan has to come on to keep the condensor cool and the high side a/c system pressures down. When the fan quits working the pressures will be so high at idle it will run very rough and nearly die. It sounds like you may need a fan assembly.
The P0072 is for the ambient temperature sensor. This is the sensor mounted out in front of the radiator that senses the temperature of the outside air. This could be a wiring issue, corrosion or water in the connector, or the sensor itself.
My plugs were replaced just recently. The engine light was off when I picked up the car. The next day, after only 2 short trips, the light came back on.
The flashing engine light has only happened on 2 occasions. When the car shows signs of hesitation, I ease off the gas and accelorate slowly. This usually bypasses any severe jerking. Most of my car usage is around town, usually under 50mph.
What signs would I look for with a bad "pcm."
If you had a bad pcm you would have a code for it, you would have a component or system that wouldn't work, or the car just plain wouldn't start. There's almost no chance you have a bad pcm. It's a $700 repair you don't want to guess at. You've got a few problems, none of them major or uncommon. I'd look into getting the wires replaced, especially before they ruin the new plugs if they are bad. If that doesn't take care of it there may be a valve sealing issue, but that's not nearly as common as flashover. Have the cooling fan operation checked, and the ambient temperature sensor looked at.
I'm asking about the pcm because it is a common problem with the 2003 pt's. Additionally, it would be covered under 80k / 8 year emmissions warranty. My car is at 71K - 6 year. Have you had many inquiries with the pt's 03 or earlier?
A bad pcm on these is not a common problem whatsoever. I've been working on these cars since they came out, along with Neons (same car) and have replaced only a couple pcms on them. If you had a bad pcm it would be very easy to diagnose. It would set a code for internal failure, it would have a component that it runs not working at all, or the car just wouldn't start. You have three seperate problems, and none of them point to the pcm at all. These are all common problems. You have a misfire likely caused by plug wires, you have a cooling fan that doesn't work, and you have an ambient temperature sensor problem.
Experience: ASE Master & Advanced level certified, Chrysler Master Certified, Trans and Hybrid Specialist