Need OBD II guru

[Titan]

My '96 mark VIII now has 213640 mi and the check engine light came on steady after doing the on and off thing for a couple weeks and the car has started to idle a little rough at times. Took it in to see what codes were there and the following were pulled:

P0720 output speed sensor circuit fault
P0133 HO2 1/1 circuit slow response
P1131 HO2 1/1 sensor indicates lean
P1270 engine RPM/speed limiter reached

the mechanic who looked at this said the last Mark he saw with this set of codes was having a wiring or PCM problem and told me to take it to the stealer to get the PCM checked out by their computer.

Any other ideas?

need to take care of this by May to pass smog, a car killer here in California

 

[keatonsdad]

Good luck. I'm no help but good luck.

 

[Right on the Mark]

All O2 codes are pointing to one only,front pass one. It could be just a old dying O2. Alot of the time I see your codes its from an exh leak right by that O2.

 

[KStromberg]

P0720 output speed sensor circuit fault

P1270 engine RPM/speed limiter reached

P0720- There are two vehicle speed sensors on the transmission. The vehicle speed sensor and output speed(or shaft) sensor. The one in question here is the OSS obviously. I would confirm harness integrity first and then check the sensor operation. If I recall correctly, the OSS is located midline on the driver's side of the transmission case underneath and is held in by one bolt NOT the one on the tailshaft. Be sure to check the condition of the o-ring also. One of these things is likely your problem. Is there any drivability issues with the car?

P1270- This code indicates that the vehicle was operated in a manner which caused engine or vehicle speed to exceed a calibrated limit. So in a nutshell the rpms reached the rev limiter. Were you messing around any time recently or getting crazy wheel slippage for any reason (mud,snow,water,ice). :shifty: If this happens to remind you of anything that happened, I wouldn't worry about it. Just clear the code when you solve these other issues and move on.


Sounds to me like the mechanic got himself overwhelmed a little too easily. From my point of view, I don't see a PCM issue here. If there is a wiring issue like he says, it is going to be associated with the harness going to the OSS and/or the o2 sensor wires if there is any wiring issue at all.

 

[Psychostang]

Clear the codes, and drive the car for 2 days. Then take it to autozone or any other parts store, and have the codes read. See which ones come back or are pending. Let us know.

 

[Titan]

I'll do that. Have had other wiring harness issues in the past. Interstate-80 where I commute was in crappy shape for a long time and beat the hell out of the car.

Guess It might be a good idea to start checking connectors