postmark2

I just filled my tank with fuel for my CL500 (MY 2000) and got a check engine light notice. On board computer said no malfunction and the light was not blinking so I drove home safely with no change in engine performance or otherwise. I have an OBD-II code reset machine and checked for stored or pending faults. I got this: PO 173 fuel trim malfunction (bank 2). I reset the light but I am wondering if someone knows exactly what caused the light to trip. I only have 46k miles on the car and it runs perfectly. Could it be I need a new O2 sensor? Thanks in advance.

PaulX608

Fuel trim codes are often related to the mass air sensor.

postmark2

Do you think I should replace the MAS then? Thanks.

PaulX608

I had mine tested at the dealership. It proved to be out of spec and was replaced under warranty. I had been telling my SA that it was the Mass Air Meter for some time, but it never had the light on when I had it in. Finally, I was going in for a new trip computer, and the light came on. I got to give him a huge 'I told you so!' when he came to me in the lounge and told me it was the Mass Air Meter. If you're no longer under warranty, it's certainly easy to replace. Let us know if that fixes it. I suspect it will.

postmark2

Thanks. I am out of warranty so I just ordered one from an online retailer I have used for years at $237.90. Hopefully I can install it myself since I DIY sometimes or would you recommend I take it to the Dealership in Alexandria?

PaulX608

I'm not 100% sure where it's located on your car, but it shouldn't be that tough to find and replace. I'm in Manassas, and I certainly wouldn't mind giving you a hand. Dealerships aren't usually too happy to install parts you buy elsewhere.

PaulX608

OK, I did a quick search, and I now know where your MAS is. Like I said, it shouldn't be too tough to DIY, but If you'd like a hand PM me and I'd be more than happy to help. Been wrenching on mine myself since the warranty expired. Always glad to assist a fellow DIY'er!

postmark2

Could you please send me an email describing where it is on my car? The MAF should be here by Friday, and if I cannot locate it, I'll try to contact you. Email address is postmark2@comcast.net. Thanks.

Jud Chapin

You might want to check that your fuel cap is on properly as if not, I believe it can set a code. I mention this only because I think your saying the light came on just after fueling. Good luck!

techbike

This is a common and often misdiagnosed problem; according to my service advisor at Rallye If the fuel cap is not replaced properly after fueling, this will turn on the check engine light. Before you spend all that money on the MAS, fix the cap and the light will go away after a few miles. This has happened to me on a E430 and the CL.

JDM

Fuel trim codes are also caused by intake manifold leaks, and fuel pressure regulators. O2 sensors tend to set specific codes, as do MAF's.

..also an air leak at an injector can cause this code.

postmark2

Thanks for all your help and suggestions. I did replace the MAS last Friday and rechecked the codes and had no pending or stored codes. I think my problem is cured. One other symptom I had was a drop in the idle when I came to a stop, which is also consistent with the bad MAF/MAS. Thanks.