1997 Pontiac Sunfire GT bank 1 too rich

This has been driving me nuts. My daughter’s car has the 2.4l 4. I’ve replaced everything over the years including both O2s, injectors, MAP, TPS, fuel regulator and plugs. I even had to replace the Cat because she tried to go over a curb and broke the flex bellows on the down pipe. The problem is it will intermittently (1-2 times a month) throw the bank 1 too rich code and light the MIL and shut off the trac lock. I used to be able to clear the codes and everything would be fine. Now I can clear the MIL but I can’t get the trac lock to work.
Anybody have any ideas short of turning the whole car into soup cans?

How about the temp sensor. It would cause the car to run rich. Trac lock is probably a wheel sensor failure. Does it throw a code?

It throws an engine code, I forget the number but the verbage on the code reader is bank 1 too rich (might be 0172 if I remember right)
I’ll look at the wheel sensors, since it’s a 97 the ABS doesn’t show any codes. My wife’s 04 Olds had issues so I bought a decent reader and it told me the right front sensor was bad…At least one “improvement” really helps the shadetree mech!

You seem to have covered about everything that would cause unregulated fuel to enter the engine i.e. leaking injector(s), leaking fuel regulator, miscalibrated MAP sensor, etc. BTW is the Inlet Air Temperature sensor in the MAP unit? The only other thing I can think of is raw fuel getting into the canister purge line or fuel contaminated engine oil i.e. vapors coming from the PCV system. A failed Coolant Temperature Sensor could be a possibility but the fuel system would not go into closed loop in the CTS was out of calibration high; the wiring was open; or the thermostat was openning too low.

This has been a tough dog because of its intermitant nature. Let us know what you finally discover that solves this problem.


How about the air filter?

Some aftermarket air filters use too much glue, are restrictive, causing a rich condition.

I must say, however, that this is an unusual occurrence.

Have you measured the fuel pressure?

Have you verified that it’s not actually too high?

Let me know if you need the fuel pressure specs. I believe I can post them for you, if needed.

Let’s see, I’m assuming you’ve verified the O2 sensors are fine, the MAP checks out, the fuel pressure regulator is ok (and varies the fuel pressure according to intake manifold vacuum as it should) and all the routine engine maintenance is up to date (plugs, air filter, timing, didn’t have the timing belt replace just prior to this happening, etc) … hmmm … well, you could have a funky injector, but my guess then is that you have an exhaust leak. What happens is that outside air gets sucked into the exhaust stream through the leak, which causes the O2 sensor to think there is more O2 in the exhaust than there should be (if it was all coming from the cylinders), so it thinks not enough fuel being injected, so the ECM injects unneeded fuel, making the mixture too rich. Look for any cracks in the exhaust system, especially the exhaust manifold, or it could be just the gasket between the exhuast manifold and the engine is leaking a bit. Maybe you could catch a break, all you need to do is re-torque the exhaust manifold bolts.

I don’t see the traction lock code being related. Confirm this with someone with expertise on your car though. Best of luck.


I’ve worked on vehicles with those exhaust leaks you’re talking about

In every instance, it has actually resulted in a P0171 lean code. The O2 sensor sees the excess oxygen as a lean condition. I’ve actually fixed many P0171 codes by simply retorquing loose exhaust manifold flange nuts and/or replacing deteriorated exhaust manifold flange gaskets.

I’m just mentioning my own personal experiences . . .

Good post @db4690; that will prove helpful to the OP’er I expect.

One add’l comment for the OP. If the engine coolant temp sensor is faulty, the sensor used by the ECM (not the dash gauge), that can make the ECM think the engine coolant is at a low temp all the time, which will cause the injectors to inject more gas than necessary, resulting in a rich mixture.

Thanks db4690 I could use the fuel pressure specs. I’ve torqued and checked the exhaust and intake. Both O2 sensors read voltage in line with what is expected (at least withing specs that I could find) The engine temp is showing ~ 195 according to the Actron reader I have. Could plugs cause this? I have to do the once over before yearly inspection and she goes back to school so I figured on oil, filters and plug change anyway. Maybe a different type of sparkplug? I’m grasping straws here. I need it to run right at least until next May. Once she graduates and gets a job We will get her something newer.


If the coolant temp sensor for the computer tells the computer the coolant never reaches the proper operating temp, the computer stays in the open loop mode. In the open loop mode, the computer doesn’t use the signals from the O2 sensor. So the computer doesn’t know if the engine is running rich or lean in the open loop mode.


Have you checked the valve clearances? Sometimes valves out of adjustment can cause a rich mixture. Like you, I’m grasping at straws here … hmmmm … Are the plugs used one of the exact part numbers recommended in the owner’s manual? If not, that could cause this kind of problem. If the part number is ok, the plugs are not likely to be the culprit, unless they are carbon fouled, or they have too wide of a gap. Maybe check the gap on one of them, see if it meets the specs for this engine… hmmm … Misfires can cause a rich mixture, any sign of that happening? Any visible cracking in the high voltage wire’s insulation?

I guess if it only needs to run until May, and it serves the purpose for now, maybe the best thing is to just live with the rich mixture and leaving the trac loc off? Let the next owner figure it out. Is that a potential solution?

Thanks all
I’m going to try checking the injectors and coils tomorrow when I do the tune up. I bought new plugs anyway and as long as it will pass inspection and makes it until may I’m happy. After that I’ll sell it for what I can get or donate for the deduction.

When it comes time to part, be sure to ask at your local high school or Jr college, they may have a auto repair class there and could use a donated car for student instruction purposes.