Check Engine Light

[super_mr2]

I have a 91' MJ 2WD w/4.0 HO (auto trans). At slightly over 120k, the check engine light came on. I replaced the O2 sensor but the light remains on. I have read conflicting info on if I need to replace the timer or can reset the light. Can anyone shine some light on this? I've searched the forum but can't seem to find anything.

 

Thanks,

Bob

[89eliminator]

i know this may sound stupid, but sometimes the check engine light will come on if your gas cap isn't all the way on. :roll:

 

(oh and where in SE WI do you live, I'm about 30 southwest of Milwaukee, as are a few others on this board)

[aerocorey]

The timer doesn't know you replaced the O2 sensor. Unplug the timer. Works on the older ones. Not sure about the HO, but try it.

 

Shouldn't that timer go off around 80,000 miles or something? Does a HO even have the timer? Might be barking up the wrong tree. Did you get it downloaded or did you just throw an O2 sensor at it because a light came on?

[HOrnbrod]

I have a 91' MJ 2WD w/4.0 HO (auto trans). At slightly over 120k, the check engine light came on. I replaced the O2 sensor but the light remains on. I have read conflicting info on if I need to replace the timer or can reset the light. Can anyone shine some light on this? I've searched the forum but can't seem to find anything.

 

Thanks, Bob

 

Yeah, my 91 CE light came on at about the same mileage. Most likely it's the preset timer that "reminds" you to change the O2 sensor, but you should run the codes first using the ignition key procedure (below). If all is well, recommend just pulling the bulb from the cluster like I did.

 

Reading Computer Codes

On 1991 to1997 models ( 1984 to 1986 V6 models as well as 1998 to 2002 follow ) you have a way of reading for fault codes which can be accessed without any scanners like other models by reading how the check engine light flashes. Start by turning the ignition key to the last stop before it starts, on and off three times within 5 seconds ending in the on position on the third time, ( i.e. on, off, on, off then on and hold ). The check engine light will start to flash quickly with a small pause in between then a medium pause to indicate the next number in the to digit number and then a long pause before the next set of flashing for the next code. If all is well you will get a code 55 which would read like this: 5 fast flashes, medium pause then a further 5 flashes. This is how all codes end with is this 55 code if you have air conditioning or with a code 33 without and any other codes would have been before it separated by a long pause. The codes will remain after this test so you can cycle through it as many times as it takes to read them. After a problem has gone the code will be removed after 50 on off key cycles or if the battery left disconnected over night which will cause a code 12 though.

 

Code Description Most likely reason

11 No crank signal to computer. Fault in wiring between crankshaft position sensor (CPS) and ECM ( PCM or computer ) or faulty CPS.

12 Battery disconnected. Battery or power to the ECM disconnected in the last 50 key cycles.

13 MAP Sensor. No change in Manifold Absolute Pressure (MAP) between engine off and on. Check circuit and MAP sensor.

14 MAP Sensor. MAP sensor voltage too high or low. Check circuit and sensor.

15 Speed sensor or circuit. No signal detected from speed sensor. Check circuit and sensor.

17 Engine running too cold. Wrong or faulty thermostat. Check also sensor and circuit for fault.

21 Oxygen sensor or circuit. O2 sensor or wiring faulty.

22 Coolant sensor or circuit. Check temp sensor and wiring.

23 Intake air temp or circuit. Check air temp sensor and wiring.

24 Throttle Position Sensor (TPS) Check TPS sensor and wiring.

25 Idle Air Control circuit (IAC) Check IAC sensor and wiring.

26 Injector circuit resistance. Peak injector current has not been reached or injector circuits have resistance

27 Fuel injector control circuit. Will need specialist diagnostics.

31 Evaporative control circuit. Fault in fuel evaporative control circuit or hoses.

33 Air conditioning clutch relay. Wiring to A/C clutch fault.

34 Cruise control circuit. Fault in circuit.

35 Cooling fan relay. Check relay and circuit.

36 Air switch solenoid circuit. Air switch solenoid circuit (non-turbo) or the waste gate solenoid on turbocharged models

37 Torque converter clutch. Needs specialist or dealer diagnostics.

41 Alternator field switch. Switch not operating correctly and check charging system.

42 Automatic shutdown relay. Check relay and circuit. Needs specialist or dealer diagnostics.

43 Misfire. Misfire in one or more cylinders.

44 Battery temperature sensor. Needs specialist or dealer diagnostics.

46 Battery over voltage. Check charging system.

47 Battery under voltage. Check charging system.

51 O2 detects lean mixture. Check sensor and circuit and for vacuum leaks.

52 O2 detects rich mixture. Check fuel injection system and sensor.

53 Powertrain Control Module. PCM (ECM) fault. Needs specialist or dealer diagnostics.

54 Distributor sync pickup. Change sync sensor in distributor.

55 End of code. Trouble codes finished or none recorded.

61 BARO solenoid BARO solenoid failure

62 Emissions reminder. Emissions maintenance reminder. Needs specialist or dealer diagnostics.

63 Controller failure. EEPROM write denied. Needs specialist or dealer diagnostics.

64 Flexible fuel sensor. Flexible fuel (methanol) sensor indicates concentration sensor input more/less than acceptable voltage

65 Manifold tune value. Manifold tune valve solenoid circuit open or shorted

66 TCM to PCM failure. No message from the Transmission Control Module (TCM) to the Powertrain Control Module (PCM)

72 Catalytic converter circuit. Needs specialist or dealer diagnostics.

76 Fuel pump bypass relay circuit. Needs specialist or dealer diagnostics.

77 Cruise control system. Check power to cruise control solenoids.

[HOrnbrod]

The timer doesn't know you replaced the O2 sensor. Unplug the timer. Works on the older ones. Not sure about the HO, but try it.

 

Shouldn't that timer go off around 80,000 miles or something? Does a HO even have the timer? Might be barking up the wrong tree. Did you get it downloaded or did you just throw an O2 sensor at it because a light came on?

 

The timer is biult into the ECU on the 91+ HOs.

[partsmj]

I think the dealer can reset it for you with the drb.

Kinda like erasing a code.

[HOrnbrod]

I think the dealer can reset it for you with the drb.

Kinda like erasing a code.

 

Yes, they can. For a fee (usually a 1-hour labor cost). :mad: I just said to h@$$ with it.

[HOrnbrod]

I'm sorry, completely blew this reply. :nuts: The ECU timer for O2 sensor replacement triggers the "Maintenance Required" light, not the "Check Engine" light. You can run the codes on the check engine light with the key procedure I posted above. As far as the Maint Req light, pull the bulb, all it does is let you know when to change the O2 sensor. Too many Millers tonight............. :cheers:

[super_mr2]

It looks as if I blew this one. It is the 'Maintenance Required' light. I didn't try the ignition code sequence yet but it looks like I'll be pulling the bulb. 89 Eliminator, I'm about 20 miles due East of you - start/end of K.

 

Later,

Bob

[89eliminator]

It looks as if I blew this one. It is the 'Maintenance Required' light. I didn't try the ignition code sequence yet but it looks like I'll be pulling the bulb. 89 Eliminator, I'm about 20 miles due East of you - start/end of K.

 

Later,

Bob

 

cool, we will have to meet up sometime. :cheers: