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Is it possible a broken exhaust was preventing the service engine soon light...

BirdOPrey5

Staff member
Administrator
VIP
from coming on, on my ZJ?

For a year or so the tailpipe was broken, the muffle was just hanging there.

It was due for inspection, including emissions. It passed emissions because the Service Engine Soon light was not on.

They fixed the exhaust and it sounds much better but after a day of driving with the fixed exhaust the Service Engine Soon light came on for the first time in years.

Coincidence? Or just the fact the exhaust is actually being pick but by a sensor further down the exhaust system?
 

John

Transplant
VIP
They could have accidentally or intentionally unhooked a sensor. Was it the same place that did a shitload of work on that avalanche?
 
I'd imagine 'catalyst efficiency' is the only code a cracked exhaust might suppress. It would have to be cracked between upstream and dowmstream O2's
 
They could have accidentally or intentionally unhooked a sensor. Was it the same place that did a shitload of work on that avalanche?
And to go further, it's possible the sensor leads were not hung proper and melted/grounded to exhaust pipe. Seen that too.
 

Ralph

VIP
Yup. Turn key on and off 3x then leave on for codes.
On a 96 the codes won't show up in the odo. You have to count flashes of the check engine light. ON-OFF-ON-OFF-ON... then count the flashes of the CEL. [5 flashes] [short pause] [5 flashes] = 55

11 IGN reference signal. Cam or crank sensors
12 Battery input to PCM disconnected during last 50 key starts.
13 Fault in the map sensor pneumatic circuit.
14 Fault in the map sensor electrical circuit.
15 Fault in the vehicle speed sensor circuit.
17 Engine running too cool.
21 Problem in the oxygen feedback circuit.
22 Fault in the coolant temperature sensor circuit.
23 Air temperature sensor.
24 Intake air temp. sensor voltage high.
25 Fault in the IAC motor drive circuit.
27 Fault in injector driver interface circuit.
33 Fault in air conditioning cutout relay circuit.
34 S/C solenoid circuits.
35 Fault in fan relay circuit.
41 Fault in the charging system or no field current.
42 Fault in the ASD relay driver circuit.
44 Battery Temp Voltage.
46 Battery voltage is too high.
47 Battery voltage is too low.
51 Lean condition is indicated.
52 Rich condition is indicated.
53 Internal problem in module.
54 No cam position signal.
55 Completion of fault code display.
62 Unsuccessful attempt to update EMR mileage.
63 Unsuccessful attempt to write to an EEPROM location by the controller.
 
they did on my 1996 zj limited... shrug

96+ is OBDII, with digital odometer. maybe 95 and earlier is what the below applies to?

On a 96 the codes won't show up in the odo. You have to count flashes of the check engine light. ON-OFF-ON-OFF-ON... then count the flashes of the CEL. [5 flashes] [short pause] [5 flashes] = 55

11 IGN reference signal. Cam or crank sensors
12 Battery input to PCM disconnected during last 50 key starts.
13 Fault in the map sensor pneumatic circuit.
14 Fault in the map sensor electrical circuit.
15 Fault in the vehicle speed sensor circuit.
17 Engine running too cool.
21 Problem in the oxygen feedback circuit.
22 Fault in the coolant temperature sensor circuit.
23 Air temperature sensor.
24 Intake air temp. sensor voltage high.
25 Fault in the IAC motor drive circuit.
27 Fault in injector driver interface circuit.
33 Fault in air conditioning cutout relay circuit.
34 S/C solenoid circuits.
35 Fault in fan relay circuit.
41 Fault in the charging system or no field current.
42 Fault in the ASD relay driver circuit.
44 Battery Temp Voltage.
46 Battery voltage is too high.
47 Battery voltage is too low.
51 Lean condition is indicated.
52 Rich condition is indicated.
53 Internal problem in module.
54 No cam position signal.
55 Completion of fault code display.
62 Unsuccessful attempt to update EMR mileage.
63 Unsuccessful attempt to write to an EEPROM location by the controller.
 

BirdOPrey5

Staff member
Administrator
VIP
They don't on my 1996 zj laredo.
If I recall I've tried before and it never worked despite having the digital odometer- maybe I (or Mom in this case) should look for the blinking light instead- I never knew to look for that, I was always looking for a code on the odometer.

Thanks, either way, we'll see.
 

Aged Punk Shredder

First World Anarchist
or spend the whole 15 buck for the OBDII scanner on amazon and the torque app and get the codes as well as common issues for your vehicle when it throws that code :shrug:
 

Ralph

VIP
or spend the whole 15 buck for the OBDII scanner on amazon and the torque app and get the codes as well as common issues for your vehicle when it throws that code :shrug:
Yup. I also have an OBD suite on my laptop so I can pinpoint issues better than with the code reader.
 
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