Bad O2 Sensor

Ok so I think I have managed to narrow down the problem with my Jeep as being a bad O2 sensor. I tried to do the diagnosis thing with the multimeter and it looked like it was in fact the problem. Since it's a Saturday night and none of the stealerships are open until monday morning doesn anyone know of what else I can look at to see what is causing my severe hesitation and rough idle on my 96 XJ 4.0. I checked the plugs and wires but are there any more of those stupid little sensors I should check?

Thanks,
Jamie

Why wait until Monday for a stealership?

Isn't there a Pep Boys or AutoZone or equivalent nearby?

I'm not sure what "thing" you did with the multimeter, but what you should have done was take a resistance reading between the two white wires on the O2 sensor connector (the ones going to the sensor, NOT the ones going to the computer) and if the sensor is in spec, it should read between 5 and 7 OHMs. If that's what you did and it was NOT reading between 5 and 7 ohms, replace the sensor.

Rough idle can be caused by numerous issues. First thing I would do is pull the error codes and look for a clue there. Since you have a '96, you can do the key "on-off-on-off-on" and the check engine light will flash error codes. If you don't have a haynes manual, get one. It will tell you in detail how to do this and what all the codes mean. Autozone is open on Sunday, so you should be able to get it.

Regards,

SimpleXJ

Thank you very much sir, what I did wasn't exactly right in checking to see if it didn't work but when I did what you said I saw that it was giving me a reading of 0 not 5 to 7 Ohms. I'll give a try at the local auto parts place tomorrow and with any luck they will have the O2 sensor I need. I've heard bad things about the Bosch O2 sensors, that's why I was hesitant about going to an auto parts place rather than from the dealer. What do you guys think? Will an auto parts place carry something that would be decent?

Thanks,
Jamie

Usually they read too high, instead of 0. 0 ohms means no resistance, or short circuit. Check the wires before you spend the money. I just got a bosch sensor from autozone - works great.

SimpleXJ

Let me know how this goes. My 99 is doing the exact same thing. Took it to auto zone and there little machine said I had "high voltage O2 sensor bank 1 sensor 1". What does all that mean?

Right so I repalced the O2 sensor in front of the cat and as would be expected we STILL HAVE THE PROBLEM!!!!! I am going to try and get the codes to see if that gives me any clues. If anyone knows of anything else I can check after that please let me know. This is officially starting to PI$$ ME OFF!!!!

That's all for now, I'll let you know what other PITA things I encounter.

Thanks,
Jamie

Ok so it looks like the problem lies somewhere either in the Map sensor and in the Automatic Shutdown Relay or control circuit according to the codes the computer gave me. I tested the MAP sensor and it looks alright as for the Relay or Circuit all the Haynes guide tells me to do is take it to the dealership. Anyone have a clue about checking/fixing that?

Thanks,
Jamie

Like I already said, check the wiring to the O2 sensor. Your haynes should give you a diagram so you can test resistance in the wires from the sensor to the ECU.

What error code are you getting? I have an FSM for a '96 so I might be able to help you.

As for your ASD relay, here's some stuff that might help you. It's out of the FSM.

HTH

SimpleXJ


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Location:


The following description of operation and tests apply only to the Automatic Shutdown (ASD) and fuel pump relays. The terminals on the bottom of each relay are numbered (Fig. 24) .



OPERATION
Terminal number 30 is connected to battery voltage. For both the ASD and fuel pump relays, terminal 30 is connected to battery voltage at all times.

The PCM grounds the coil side of the relay through terminal number 85.

Terminal number 86 supplies voltage to the coil side of the relay

When the PCM de-energizes the ASD and fuel pump relays, terminal number 87A connects to terminal 30. This is the Off position. In the off position, voltage is not supplied to the rest of the circuit. Terminal 87A is the center terminal on the relay.

When the PCM energizes the ASD and fuel pump relays, terminal 87 connects to terminal 30. This is the On position. Terminal 87 supplies voltage to the rest of the circuit.

TESTING
The following procedure applies to the ASD and fuel pump relays.



Remove relay from connector before testing.
With the relay removed from the vehicle, use an ohmmeter to check the resistance between terminals 85 and 86. The resistance should be between 75 +/- 5 ohms .
Connect the ohmmeter between terminals 30 and 87A. The ohmmeter should show continuity between terminals 30 and 87A.
Connect the ohmmeter between terminals 87 and 30. The ohmmeter should not show continuity at this time.
Connect one end of a jumper wire (16 gauge or smaller) to relay terminal 85. Connect the other end of the jumper wire to the ground side of a 12 volt power source .
Connect one end of another jumper wire (16 gauge or smaller) to the power side of the 12 volt power source . Do not attach the other end of the jumper wire to the relay at this time. WARNING: Do not allow ohmmeter to contact terminals 85 or 86 during this test.



Attach the other end of the jumper wire to relay terminal 86. This activates the relay. The ohmmeter should now show continuity between relay terminals 87 and 30. The ohmmeter should not show continuity between relay terminals 87A and 30.
Disconnect jumper wires.
Replace the relay if it did not pass the continuity and resistance tests. If the relay passed the tests, it operates properly. Check the remainder of the ASD and fuel pump relay circuits.
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The two error codes I am getting for my 96 XJ are (1) four flashes--pause--two flashes and (2) five flashes--pause--five flashes. From what I can gather that means an error code 14(MAP Sensor) and 42(Automatic Shutdown Relay or control circuit).

Tomorrow morning I will do the test you have sent me for the ASD Relay and see what I find. I did the Haynes test for the MAP sensor and it looked like it should have been fine according to what they were saying with the resistance.

-Jamie

I don't see how you're getting code 14 from the flash pattern you wrote. four flashes pause two flashes IS code 42, BUT where did you come up with 14?

Code 42 has 6 possibilities. My FSM lists no specific P codes for the different variations of code 42. I'm not sure why. That might be a good question to call jeep and ask about.

Possible causes of code 42:

ASD control circuit
Fuel sending unit volts too high
Fuel sending unit volts too low
Fuel sending unit showed no change over miles
Fuel pump relay control circuit
No ASD relay output voltage at PCM

SimpleXJ

Opps my bad, you're right it is a code 42 I am going to check the relay like you said and I'll let you know what I find.

thanks,
Jamie

The problem was a bad ASD relay. Seems to be running like a champ now, I'll have to pray to the Jeep Gods and also thanks to you SimpleXJ. I couldn't have done it without your help.

Thanks a million,

Jamie

No problem, glad we could help!

Regards,

SimpleXJ