Q: AC failed and started running rough and the Check Engine Light came on. But NOW its fine.

asked by on

I have a 2007 Reno and was taking a long trip. I left home on a full tank of gas and about an hour and 20 minutes into the trip It started running rough and I noticed the check engine light had come on. Also the A/C, which had been working was no longer blowing cold at all. I stopped at a Auto Parts store and checked the codes, which were as follows. P2106, P0452, P0405, P0107, P0651, P0606 and misfires and all 4 cylinders P0300 and P0301-302-303-304. I want to point out that the car ran fine for 130 miles before I had any issues. Googling and asking advice from non-mechanics seemed to indicate that bad gas may have caused these issues so I added some fuel additive (sea-foam motor treatment) and added gas up to 3/4 of the tank. That was almost 2 weeks ago. Since then it has been running a little rough and with no power. I was prepared to drain the gas tank and replace the spark plugs when today noticed it was driving normally and the CEL had gone off, but the A/C isnt working. WTF?

My car has 90000 miles.
My car has a manual transmission.

I wouldn’t concern yourself with the timing of your cars symptoms. When a car fails, I liken it to when a light bulb decides to burn out. It was just its time. Everything will eventually fail. I also would strongly disagree with the bad gas theory. This idea is a common cause that is often pointed at, but the reality is it is rarely if ever true. The only time you could get bad gas is if the fuel you had used had been sitting in an unsealed container for several years. It just isn’t very likely.

I can speak to all the codes you have listed. Thanks for listing them by the way. I can derive a few conclusions with them. When we see this many codes, it is time to consider what could be responsible for all these codes. It extraordinarily unlikely that all these components related to these codes failed at exactly the same time. The one common thing between all these components is the PCM. In particular, the 5 volt reference, which is supplied by the PCM. Without explaining the purpose of the 5 volt reference, I will say it is integral in the accurate measuring of the vehicles sensors. If this signal is corrupted, it will cause many failures and codes as you see here.

The 5 volt reference is most commonly corrupted by a sensor that is failing. In your case, I would clear the codes and see if they all come back or if one or a few appear. This will often set us down the correct diagnostic path. Most often, there is a sensor that has a short in it that caused the 5 volt reference to be corrupted. The PCM will not have accurate information and all the systems will go into a default mode.

It could also be the PCM. Diagnosing such a problem requires knowledge of every system in the car. So if you are not intimately familiar with them, or don’t want to take on the learning that will be involved to diagnose your symptoms, I recommend having one of our mobile technicians diagnose the trouble codes for an accurate repair.

Good luck! These can be tricky.

Was this answer helpful?
The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details
  1. Home
  2. Questions
  3. AC failed and started running rough and the Check Engine Light came on. But NOW its fine.

Get an instant quote for your car

Our certified mechanics come to you ・Backed by 12-month, 12,000-mile guarantee・Fair and transparent pricing

Get a quote

What others are asking

Q: What Is the Problem When the Check Engine Light Comes On?

The Check Engine Light is on most vehicles built in the last twenty years. The light is used to alert the operator of the vehicle that there is a problem that needs to be looked at as soon as possible....

Q: Once engine is warmed up (3-4miles) car stalls at intersections and won't stay running.

Hi there. The correct way to diagnose most mechanical problems like you are describing begins with a digital scanner inspection. This allows the mechanic to download any stored error codes and then pinpoint the source of the issue. Once codes...

Q: Where is the fuel injector located in a 2011 Kia Soul

Hi there. The fuel injectors are located on intake manifold on a Kia four-cylinder engine. It might be a good idea for you to purchase a service and repair manual for your 2011 Kia Soul if you're planning to do...

Related articles

P0240 OBD-II Trouble Code: Turbocharger Boost Sensor B Circuit Range/Performance
P0240 code definition Turbocharger Boost Sensor B Circuit Range/Performance What the P0240 code means P0240 is an OBD-II generic code triggered when the Engine Control Module (ECM) detects the intake boost...
How to Avoid Back Pain in a Car
If you have back problems, sitting in a car for an extended period of time can be excruciating. Even without back problems, you could experience discomfort and soreness from...
P2103 OBD-II Trouble Code: Throttle Actuator Control Motor Circuit High
P2103 means there is a fault with the throttle actuator control motor circuit, likely due to a defective electrical component or part.