just bought my girlfriend a 2001 accord with the ulev motor, drove the car home and the CEL popped on, brought it to autozone, checked the codes, P0420 (catalytic converter), P0500 (speed sensor), and P1164 (Upstream O2 sensor).

after the car warmed up it kicked itself into LIMP mode, wont rev over 4k rpm and acts like it at redline, dont think the vtec is kicking in either.

replaced the speed sensor, figured the O2 sensor wouldnt cause the car to stay in LIMP mode, i was wrong.

FIRST- if i replace the bank 1 O2 sensor could that fix my cat problem? trying to avoid replacing the cat itself.

SECOND- why is the car still in LIMP mode after i replaced the speed sensor? Could the O2 sensor be keeping the car in LIMP mode?

 

A low emissions car may stay in limp mode when key sensor such as primary Air/Fuel sensor is indicating a performance fault. Shop manuals do not describe conditions where the rev limit is enabled.

Shop manual indicates to reset PCM, start and run engine at 3K rpm until radiator fans come on. Check for a temporary DTC w/ scanner. If P1164 is indicated, the A/F sensor should be replaced.

If Check Engine Light stays off, then drive car in D3 starting from 1k rpms to full throttle for at least 5 secs, then decelerate w/ closed throttle for 5 secs. Repeat unil CEL comes on or emissions readiness completed is determined. If P1164 is set, then A/F sensor should be replaced.

good luck

 

thanks Texas, also, is there any chance replacing the O2 sensor will remove the cat code as well? i dont want to spend $200 on a bolt up flowmaster if i dont have to, and im not buying anything universal that needs to be welded

 

Yes, a malfunctioning AF sensor could lead to code P0420 and it's worth waiting to see if code disappears and does not return.

It is also possible perhaps likely that faulty AF sensor has damaged the converter and code may re-appear.

You can find aftermarket bolt-on converters on Amazon, Ebay, etc.

good luck

 

i appreciate the help, ill let everyone know what happens after i change the O2 sensor.

 

swapped out the o2 sensor, which fixed the Catalytic converter p0420 code, and took the car out of limp mode....

but its still throwing the P1164 O2 sensor code O.o

confused as ****.

 

Shop manual says to reset ECM, test drive and see if code P1164 returns. If yes, then search for intermittent wiring or connector fault at connector C102 under the underhood fuse box, AF sensor connector, wiring and ECM. Note, a constant open or short would have set another code, P0131 or P0132.

If all wiring faults are ruled out the ECM is likely the problem.

Note, resetting ECM will make P0420 temporarily disappear. If you haven't completed the obd2 catalyst efficency test, then it's early to say cured. I wouldn't worry about P0420 until P1164 is resolved.

good luck

 

i was thinking it may be a faulty sensor, before i changed it, it would take 30-50 miles for the code to come back on, now that i replaced it, the code comes back withing 60 seconds of clearing.

going to swap the sensor out for another one tonight before i start cutting up the harness casing looking for a break in the wire.

 

Did you install an Air/Fuel sensor? You keep calling it an oxygen sensor and although one might install/connect, it will not function correctly.

Suggest checking wiring by disconnecting at the ECM and checking each line for short to ground. Next sequentially short each line to ground at the AF sensor connector and check for ground available at the ECM connector. If both these checks are good, wiring is OK.

good luck

 

well when i call the part store they tell me that they dont sell air fuel ratio sensors, only 02 upstream and downstream, all the research i have done so far leads me to believe the upstream o2 sensor is the air fuel ratio sensor.