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1997 Cadillac STS


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Hey Guys,

I have a 1997 Cadillac STS and am in need of some help.

When you fire it up it is running really rough. It feels like it running on about 5 cylinders.

I have checked the codes and they are coming back as

P0101 MAF Sensor Performance.

P0135 Heated Oxygen Sensor Bank 1 Sensor 1

My question is this why it would be running terriable.

Also which Oxygen sensor is this reffering too. I do not know which one this is on the car.

Also where is the MAF sensor located. I thought it was the sensor right on top of the intake/throttle body area and you can see it when you remove the northstar cover off the top.

Can someone please help me and tell me what steps I could go about fixing these problems and making the vehicle run good again.

Thank You Very Much, Jason Worker

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The MAF is the mass airflow sensor, which is in the intake side of the throttle body. The oxygen sensor that the DTC is referring to is the top rear oxygen sensor. The most likely culprit isthe fuse labeld OXY SEN 2 in the engine compartment fule/relay center (10 A), which supplys power to heat that oxygen sensor. While you are looking at fuses, look at the one labeled ECS (10 A) because it is the one that supplies power to the MAF sensor.

If the MAF DTC is set, the PCM will disable the traction control and the transmission will take off in second gear. That probably accounts for what seems like sluggish performance. The mixture control is hurt too but you would probably see that in gas mileage, but not a really bad performance hit.

The first things to check for the MAF sensor DTC, according to the factory shop manual (FSM) page 6-302 are the air cleaner element and intake duct. Make sure that it has a clean, properly installed air cleaner element, that the air cleaner housing is properly seated and locked onto the left front wheel well over the PCM (the finned aluminum housing under the air cleaner), and that the intake air duct is properly seated on both the air cleaner housing and the throttle body, and that it is not kinked or collapsed. If that is all OK, take off the intake duct at the throttle body and shine a flashlight in and look for debris or obstruction on the MAF, which is a grid preceding some fine wires. While you are there, make sure that the throttle body spacer is tight, and the MAF sensor seal is OK.

The next thing to check is the PCV valve. If it is missing or stuck open, it can cause this DTC. Then, look for other vacuum leaks. Check the power brake vacuum line, the EGR valve, plate and tubes, and make sure that the intake manifold bolts are not loose and the intake manifold gasket is not torn or folded over on itself.

I'm getting my information from the FSM; I haven't had this problem or fixed it myself. Those who have had experience in clearing either or both DTCs will likely chime in too.

-- Click Here for CaddyInfo page on "How To" Read Your OBD Codes
-- Click Here for my personal page to download my OBD code list as an Excel file, plus other Cadillac data
-- See my CaddyInfo car blogs: 2011 CTS-V, 1997 ETC
Yes, I was Jims_97_ETC before I changed cars.

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