Check Engine light

I have a '96 XJ with a 5-speed just about to hit 100K. The check-engine light just came on, but I didn't notice any driveability problems. I remember reading somewhere that the CEL will automatically come on at some point to remind you to change the O2 sensor, but I thought that was supposed to have happened at more like 70K. The light has never come on until now. Any ideas?

pull the codes. the check engine light in a 96 doesn't come on because of a preset mileage. It comes on when there is an error code. Go to autozone and get a free code reading done, or flip the key ON-OFF-ON-OFF-ON and the check engine light will flash the codes. It does 10's first and 1's after a pause.... so flash flash pause flash flash flash would be code 23. Make sense?

SimpleXJ

jkellner said:

I have a '96 XJ with a 5-speed just about to hit 100K. The check-engine light just came on, but I didn't notice any driveability problems. I remember reading somewhere that the CEL will automatically come on at some point to remind you to change the O2 sensor, but I thought that was supposed to have happened at more like 70K. The light has never come on until now. Any ideas?

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My 94 had the same problem but my header was cracked that made my check engine light come on often.

Cel

The light went out now, but I got the codes before it went out. Now can somebody tell me what these codes refer to? I got three: 12, 14 and 56.

SimpleXJ said:

pull the codes. the check engine light in a 96 doesn't come on because of a preset mileage. It comes on when there is an error code. Go to autozone and get a free code reading done, or flip the key ON-OFF-ON-OFF-ON and the check engine light will flash the codes. It does 10's first and 1's after a pause.... so flash flash pause flash flash flash would be code 23. Make sense?

SimpleXJ

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jkellner said:

The light went out now, but I got the codes before it went out. Now can somebody tell me what these codes refer to? I got three: 12, 14 and 56.

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12--Battery disconected within last 50 key on cycles
14--MAP sensor voltage too high or low.Check sensor and circut.Replace sensor
56--? not a code.55-maybe? End of code output.
Wayne

Cel

I don't know why I got 12. I know the battery hasn't been disconnected recently, but I'll look into 14 the MAP sensor. I don't know how to test the sensor, and I don't have a voltmeter. Should I just replace the thing? What kind of symptoms does a bad MAP produce? I noticed when I cold-start the Jeep, it sometimes doesn't idle high, like it's in warm-up mode -- it just starts and hovers around 800 RPM. I thought it might be the coolant temp sensor, but would a bad MAP cause that too? I didn't get any other codes.

Wayne Sihler said:

12--Battery disconected within last 50 key on cycles
14--MAP sensor voltage too high or low.Check sensor and circut.Replace sensor
56--? not a code.55-maybe? End of code output.
Wayne

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Code 14 could be one of two codes - MAP voltage high OR low, as Wayne said. You need to figure out which one is going on before doing anything else. The MAP sensor should be getting around 5v supply. You do need a voltmeter for this. Just buy one, they're cheap. It'll be a lot less money for a meter than a new sensor. At $90 a pop you better be sure the sensor is bad first. A meter can be had for $20.

Anyway, if you get one, unhook the connector to the sensor, put the red meter lead into the 5v supply wire, and black meter lead into the ground wire on the connector. You should be getting around 5v. If you are getting more, then the code is "voltage too high" if its low the code is "map voltage too low". Also check the little rubber hose under the sensor that pulls vaccuum off the manifold.

Your best bet would probably be to get a haynes manual to help you along. Autozone can also scan your codes and tell you exactly which one of the two you've got. But what fun is that?

Here's a diagram of which wire is what on the MAP connector. Your is the top one - XJ body.



SimpleXJ

OK. I'll test at the connector. But then what? What is the remedy for "voltage too high." And then, what is the remedy for "voltage too low"? Seems neither of these indicates a fault with the sensor itself if I'm testing at the connector. I do have the Haynes manual. Will this tell me what to do when I figure out too low or too high?

SimpleXJ said:

Code 14 could be one of two codes - MAP voltage high OR low, as Wayne said. You need to figure out which one is going on before doing anything else. The MAP sensor should be getting around 5v supply. You do need a voltmeter for this. Just buy one, they're cheap. It'll be a lot less money for a meter than a new sensor. At $90 a pop you better be sure the sensor is bad first. A meter can be had for $20.

Anyway, if you get one, unhook the connector to the sensor, put the red meter lead into the 5v supply wire, and black meter lead into the ground wire on the connector. You should be getting around 5v. If you are getting more, then the code is "voltage too high" if its low the code is "map voltage too low". Also check the little rubber hose under the sensor that pulls vaccuum off the manifold.

Your best bet would probably be to get a haynes manual to help you along. Autozone can also scan your codes and tell you exactly which one of the two you've got. But what fun is that?

Here's a diagram of which wire is what on the MAP connector. Your is the top one - XJ body.

SimpleXJ

Click to expand...

Once you are sure you're getting the proper supply voltage to the sensor, you can start trouble shooting the sensor itself.

BTW, No 5 volt supply to the MAP sensor will cause code 14 also.

To test the sensor:

-set your meter to read volts
-with the sensor connected, from the backside of the connector do the following:
-connect red meter lead to sensor signal wire (middle)
-connect black meter lead to sensor ground
-start the vehicle
-verify that at idle voltage is between 0.5 and 1.8 volts
-verify that at WOT (wide open throttle) voltage reaches 3.9-4.8 volts

if voltage is not as specified, vaccuum supply to the sensor or the sensor itself is bad.



SimpleXJ

Cel

I read through the procedures for the MAP sensor in the Haynes manual as well. But it goes through testing for MAPs mounted on the firewall. Mine (1996) is on the throttle body and it suggests having dealer service do the testing. Can I still test using the procedures below? I'm not too worried though, as the check-engine light is not on anymore and it's running fine.

SimpleXJ said:

Once you are sure you're getting the proper supply voltage to the sensor, you can start trouble shooting the sensor itself.

BTW, No 5 volt supply to the MAP sensor will cause code 14 also.

To test the sensor:

-set your meter to read volts
-with the sensor connected, from the backside of the connector do the following:
-connect red meter lead to sensor signal wire (middle)
-connect black meter lead to sensor ground
-start the vehicle
-verify that at idle voltage is between 0.5 and 1.8 volts
-verify that at WOT (wide open throttle) voltage reaches 3.9-4.8 volts

if voltage is not as specified, vaccuum supply to the sensor or the sensor itself is bad.



SimpleXJ

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