About a month ago, I got a SES light and pulled the codes. One was 09-01 for the right (rear) O2 sensor and if I remember right, 01-15 for a lean condition on the right bank. I figured, with 101k miles on my '97 SE 5-speed, it was time for new O2 sensors anyhow, so, I replaced all my O2 sensors.

Well, the 09-01 code comes on and I also get 03-07 which is the ECM closed loop logic for the left bank.

However, if I clear the SES light after the car is warmed up, I can go 5 miles or so prior to the SES light coming on. From a cold start (and its cold now) it's only abot a mile and a half before the SES comes on.

The funny thing is, replacing the O2 sensors really smoothed out the engine. I lost a seeming "flat" spot in torque between 3000 to 3700 rpm. Also, prior to the SES coming on, in 2nd gear down shifts around a tight turn in town, the Max just started, every now and then to balk. That is all gone now. The car itself runs incredibly well.

However, there's that pesky SES light. It's been about 600 miles of driving since relacing the O2 sensors. What's up? Is the ECU still reprograming itself. It does seem to be getting smoother and smoother. Or, do I have a harness wiring problem or what. I hate to take it to the dealer, but...

I would greatly appreciate any comments here.

I really take care of my Max, bought it new in the spring of '97. I keep all my fluids fresh and run M1 in the engine and MT90 in the trans axle. If you've read thisd far, here's a nice tip for 5-speed owners. Grease that ball and socket joint, it really smooths out your shifting. I put in a short shifter on my P5 and that got me thinking of the Max (it had 90k miles at that point). I had recently put in a fresh batch of MT90 and had hoped for some smoother shifting. Well, I unscrewed the shift **** and gently pried off the plastic shift cover piece and lo and behold the factory grease had turned into a nasty dried out and caked substance. Being too lazy to pull it apart further, I used a needle type grease applicator fitting from a farm machinery parts departjment farmers use for greasing "sealed" bearings, and worked in some Redline synthetic grease.

Voila! A vastly improved smoothness to the shifter.

 

Bump. I don't see how I can have a wiring problem as I would think the SES light would come on very quickly in that case. Is the ECU still reprograming itself?

 

have you tried resetting the ecu?

 

Yes. I've cleared the SES light by turning the screw clockwise to stop for 2 seconds and then repeating. The SES is then off when it starts. It stays off as I described above.

 

By re-setting the ECU, you mean disconnecting the battery for 10 minutes or so, then starting and letting idle a bit. well, I tried that. Same thing, SES light comes on around 5 minutes of driving.

Boy was i p&*^%!. So I thought, maybe the connector from my brand new OEM rear sensor is going up against a slightly corroded wiring harness connector. Guess I'll pop the hood and spray a little WD-40 on the connectors and re-connect.

So, I popped the hood, flashlight and WD-40 in hand and looked at the connectors - THEY WERE COMPLETELY APART!

Am I stupid or what. Now, don't get me wrong, I had connected them when I put in the new O2 sensor, but I guess a bit of accumulated deposit had kept things from clicking together tightly.

Moral of the story:

1. CHECK THE OBVIOUS.
2. If a wiring harness connector hasn't been undone in 100,000 miles, maybe it's best to spray on a little WD-40 to facilitate a nice re-connection.

Can you imagine what the dealership might have done to me on this one if I had taken it in?

Right now, my '97SE 5-speed is running absolutely perfectly. Replacing the O2 sensors has made a BIG difference in smoothness under hard acceleration.

 

Wait, you can reset the ECU by pulling the battery for 10 minutes? That sounds easier than tweaking the with the ECU.

 

Honestly, I'd stay away from putting WD-40 on electrical connectors.. true enough it will do a super job of getting rid of the corrosion, but it doesn't fully evaporate, and it doesn't conduct electricity, so you could end up with a problem down the road. Also, it's going to attract dirt & debris.. At least use it then clean it off with some rubbing alchohol.. There's also cleaners available specifically for electrical connectors at pep boys or wherever..