Check Engine Light

Home For Beginners Glenn's Jeep Trails Jeep Humor Gears Check Engine Light GPS Tech Tips Jeep History Tow Vehicle Camper Motorcycles Links What's New Disclaimers

Ah, yes!  The infamous TJ Check Engine Light; official designation, the Malfunction Indicator Lamp (MIL).  If you have a TJ, then you have most likely had this stupid light come on one time or another.  What does it mean?  What do you do when it comes on?  And, most importantly, how do you turn the blasted thing OFF ?!?!?

There's been a lot of discussion on various newsgroups and e-mail lists about this "problem".  Dirt Road Magazine has a page called "TJ Error Codes" at http://www.dirtroad.com/codes.htm, which explains the procedure for determining the applicable "error code", and a table describing what each code means.  For your convenience, I've included this same information below; but I've also included additional information on how the whole On-Board Diagnostics (OBD) system works as well.

The Powertrain Control Module (PCM) (a.k.a., the computer or "black box") pictured to the left, is mounted to the firewall, under the hood, just above the battery.  Its job is to monitor numerous different circuits in the fuel injection, ignition, emission, and engine systems.  If the PCM senses a problem with a monitored circuit often enough to indicate an actual problem, it stores a Diagnostic Trouble Code (DTC) (a.k.a., an Error Code), in the PCM's memory.  Diagnostic trouble codes that affect vehicle emissions will cause the Malfunction Indicator Lamp (MIL) (a.k.a., the Check Engine Light) to illuminate continuously while the engine is running.  If the problem is repaired or ceases to exist, the PCM cancels the code after 40 warm-up cycles and the Malfunction Indicator (check engine) Lamp will go out. 

Note:  Diagnostic Trouble Codes are the results of a system or circuit failure, but do not directly identify the failed component or components.

A service technician can display a Diagnostic Trouble Code (DTC) in three different ways (you and I can use two of these methods, unless you have access to a "DRB Scan Tool"; I don't): 

  1. a two-digit number flashed on the Malfunction Indicator (check engine) Lamp
  2. a two-digit number displayed on the vehicle odometer
  3. using a DRB Scan Tool, plugged into the 16-way Data Link (diagnostic) Connector under the dash on the driver's side (pictured to the right)

 

bullet

To determine which Diagnostic Trouble Code(s) are stored in the PCM of your '97 TJ:
bullet

Turn the ignition key to the "On" position three times in succession (i.e., On, Off, On, Off, On), within five seconds

bullet

The Malfunction Indicator (Check Engine) Lamp will flash the appropriate number of times to indicate the DTC number, with a short pause between the first and second digits  (e.g., 2 flashes of the MIL, followed by a short pause, followed by 5 more flashes, indicates error code 25)

bullet

The appropriate DTC will also be displayed in the odometer window

Note: All DTCs consist of 2 digits (see table below).  If more than one DTC is stored in the PCM's memory, the procedure above will display all codes in succession.  Regardless of how many codes are stored, Code 55 will always be the final code to be displayed.  Code 55 indicates the "completion of the fault code display on the Check Engine lamp".

bullet

How to turn OFF the Check Engine Light

First of all, your Check Engine Light probably came on for a good reason.  However, if you were doing something funky on the trail, the problem has most likely already corrected itself as soon as you got things back under control.  Therefore, as stated in the Powertrain Control Module discussion above, "if the problem is repaired or ceases to exist, the PCM cancels the code after 40 warm-up cycles and the Malfunction Indicator (check engine) Lamp will go out."  This means that, depending on how many times you stop and restart the engine during the remainder of the ride, the light may very well go out before you hit the trail end.  Otherwise, it will go out during the next few days (or maybe weeks).  To get it to do out sooner, I'm told that if you disconnect the battery for a few minutes, that will reset the computer and turn off the light.  However, if there's still a valid malfunction, the light will most likely come back on again, and you should probably take your Jeep in for a professional diagnosis and service.

 

bullet

Diagnostic Trouble (Error) Code Descriptions:

MIL
Code

DRB Scan
Tool Display

 Description of Diagnostic Trouble Code
11* No Crank Reference Signal at PCM No crank reference signal detected during engine cranking
11** Intermittent Loss of CMP or CKP, or Misfire Adaptive Numerator at Limit Intermittent loss of either camshaft or crankshaft position sensor, or CKP sensor target windows have too much variation
12* Battery Disconnect Direct battery input to the PCM was disconnected within the last 50 key-on cycles
13** No Change in MAP From Start to Run No difference recognized between the engine MAP reading and the barometric (atmospheric) pressure reading from start-up
14** MAP Sensor Voltage Too High (or Too Low); or No 5 Volts To MAP Sensor MAP sensor input above the maximum (or below the minimum) acceptable voltage; or 5 Volt output to MAP sensor open
15** No Vehicle Speed Sensor Signal No vehicle speed sensor signal detected during road load conditions
17* Engine Is Cold Too Long Engine did not reach operating temperature within acceptable limits
17** Closed Loop Temp Not Reached Engine does not reach 20ºF within 5 minutes with a vehicle speed signal
21** Left O2 Sensor Shorted to Voltage Left oxygen sensor input voltage maintained above the normal operating range
21** Upstream O2 Sensor Shorted to Ground; or Upstream O2 Sensor Heater Failure; or Upstream O2 Sensor Slow Response Upstream O2 sensor voltage too low, tested after cold start; or Upstream oxygen sensor heating element circuit malfunction; or Upstream oxygen sensor response slower than minimum required switching frequency
21** Downstream O2 Sensor Shorted to Ground; or  Downstream O2 Sensor Heater Failure; or Downstream O2 Sensor Shorted to Voltage Downstream O2 sensor voltage too low, tested after cold start; or Downstream oxygen sensor heating element circuit malfunction; or  Downstream oxygen sensor input voltage maintained above the normal operating range
22** ECT Sensor Voltage Too High (or Too Low) Engine coolant temperature sensor input above the maximum (or below the minimum) acceptable voltage
23** Intake Air Temp Sensor Voltage Too High (Too Low) Intake air temperature sensor input above the minimum (or below the maximum) acceptable voltage
24** Throttle Position Sensor Voltage High (or Low); or TPS Voltage Does Not Agree With MAP Throttle position sensor input above the maximum (or below the minimum) acceptable voltage; or TPS signal does not correlate to MAP sensor
25** Idle Air Control Motor Circuits; or Target Idle Not Reached An open or shorted condition detected in one or more of the idle air control motor circuits; or Actual idle speed does not equal target idle speed
27** Injector Control Circuit Fuel injector output driver does not respond properly to the control signal
31** EVAP Purge Solenoid Circuit; or EVAP Purge Flow Monitor Failure An open or shorted condition detected in the duty cycle purge solenoid circuit;  or  Insufficient or excessive vapor flow detected during evaporative emission system operation
33* A/C Clutch Relay Circuit An open or shorted condition detected in the A/C clutch relay circuit
34* Speed Control Solenoid Circuits; or Speed Control Switch Always Low An open or shorted condition detected in the Speed Control vacuum or vent solenoid circuits;  or Speed Control input below the minimum acceptable voltage
37* Torque Converter Clutch, No RPM Drop At Lockup Relationship between engine speed and vehicle speed indicates no torque converter clutch engagement (auto trans only)
37** Torque Converter Clutch Solenoid Circuits; or Park/Neutral Switch Failure An open or shorted condition detected in the torque converter part throttle unlock solenoid control circuit (3 speed auto RH transmission only);  or  Incorrect input state detected for the Park/Neutral switch (auto trans only)
41*** Generator Field Not Switching Properly An open or shorted circuit detected in the generator field control circuit
42* Auto Shutdown Relay Ctrl Circuit; or No ASD Relay Output Voltage at PCM; or Fuel Pump Relay Control Circuit; or Fuel Level Sending Unit Volts Too High (or Too Low); or Fuel Level Unit No Change Over Miles An open or shorted condition detected in the auto shutdown relay circuit; or An open condition detected in the ASD relay output circuit; or An open or shorted condition detected in the fuel pump relay control circuit;  or Shorted (or open) circuit between PCM and fuel gauge sending unit; or No movement of fuel level sender detected
43* Ignition Coil #1 Primary Circuit Peak primary circuit current not achieved with maximum dwell time
43** Multiple Cylinder Misfire; or Cylinder #1, or #2, or #3, or #4, or #5, or #6 Misfire Misfire detected in multiple cylinders; or Misfire detected in cylinder #1, or #2, or #3, or #4, or #5, or #6
44** Battery Temp Sensor Voltage Too High (Too Low) Battery temperature sensor input voltage above (below) an acceptable range
46*** Charging System Voltage Too High Battery voltage sense input above target charging during engine operation
47*** Charging System Voltage Too Low Battery voltage sense input below target charging during engine operation.  Also, no significant change detected in battery voltage during active test of generator output circuit
51** Fuel System Lean A lean air/fuel mixture has been indicated by an abnormally rich correction factor
52** Fuel System Rich A rich air/fuel mixture has been indicated by an abnormally lean correction factor
53** PCM Failure; or Internal Controller Failure  PCM internal fault condition detected
54** No Cam Signal at PCM No camshaft signal detected during engine cranking
55*

 N/A

 Completion of fault code display on the Check Engine Lamp (MIL)
63* PCM Failure EEPROM Write Denied Unsuccessful attempt to write to an EEPROM location by the PCM
64** Catalytic Converter Efficiency Failure Catalyst efficiency below required level
65* Power Steering Switch Failure Power steering high pressure seen at high speed (2.5L only)
72** Catalytic Converter Efficiency Failure Catalyst efficiency below required level
77* S/C Power Relay Circuit Malfunction detected with power feed to speed control servo solenoids

* = This DTC will not cause the Check Engine Lamp (MIL) to illuminate.  However, if another problem causes the MIL to illuminate, and this code is identified when you display all of the codes, at least you will know what it means.

** = The Check Engine Lamp (MIL) will illuminate during engine operation if this DTC is recorded.

*** = Generator Lamp will also be illuminated if this DTC is recorded.

Source: 1997 Jeep Wrangler Factory Service Manual; Group 25, Emission Control Systems.

tj-front-icon.gif (1299 bytes)

[ Home ] [ For Beginners ] [ Glenn's Jeep ] [ Trails ] [ Jeep Humor ] [ Gears ] [ Check Engine Light ] [ GPS ] [ Tech Tips ] [ Jeep History ] [ Tow Vehicle ] [ Camper ] [ Motorcycles ] [ Links ] [ What's New ] [ Disclaimers ]

 

                    Copyright 1998 - 2008 Ó by Glenn Bontly