OBD (On-Board Diagnostic) systems

Location and pinouts for the Diagnostics Connector

OBD systems are found in most vehicles in use today. OBD is an electronic system designed to control engine functions and diagnose engine problems or component failures, as well as minimize emissions. OBD-II, a new standard introduced in cars built after January 1, 1996, provides almost complete engine control and also monitors parts of the chassis, body and accessory components, as well as the diagnostic control network of the vehicle.

OBD-II equipped vehicles have a connector located in the passenger compartment, usually accessible from the driver's seat (under the dash above the hood release lever in the Grand Cherokee WJ). A cable is plugged into the OBD-II connector and connected to a scanning tool. This can range from a simple hand-held meter that provides a coded read-out of the various diagnostic functions, up to a large console computer-based unit costing thousands of dollars.

Fault codes usually appear after the "Check Engine" light has come on. The data provided by the OBD-II system can sometimes pinpoint the specific component that has malfunctioned, saving substantial service time and cost. Scanning OBD-II signals can also provide important information when purchasing a used vehicle. Recent introductions of less costly scanning devices have allowed home mechanics and small shops accessibility to OBD-II signals to use them for their own testing and repairs.

Malfunction Indicator Lamp (MIL)

In the Grand Cherokee WJ, the MIL gives an indication to the vehicle operator when the Powertrain Control Module (PCM) has recorded a Diagnostic Trouble Code (DTC) for an On-Board Diagnostics II (OBDII) emissions-related circuit or component malfunction. The MIL is controlled by a transistor on the instrument cluster circuit board based upon cluster programming and electronic messages received by the cluster from the PCM over the Programmable Communications Interface (PCI) data bus.

The MIL bulb is completely controlled by the instrument cluster logic circuit, and that logic will only allow this indicator to operate when the instrument cluster receives a battery current input on the fused ignition switch output (run-start) circuit. Therefore, the bulb will always be off when the ignition switch is in any position except On or Start. The bulb only illuminates when it is provided a path to ground by the instrument cluster transistor.

The instrument cluster will turn on the MIL for the following reasons:

BULB TEST - Each time the ignition switch is turned to the On position the MIL is illuminated for about three seconds as a bulb test.

MIL LAMP-ON MESSAGE - Each time the cluster receives a MIL lamp-on message from the PCM, the indicator will be illuminated. The indicator can be flashed on and off, or illuminated solid, as dictated by the PCM message. For some DTC’s, if a problem does not recur, the PCM will send a lamp-off message automatically. Other DTC’s may require that a fault be repaired and the PCM be reset before a lamp-off message will be sent.

COMMUNICATIONS ERROR - If the cluster receives no lamp-on or lamp-off messages from the PCM for twenty consecutive seconds, the MIL is illuminated by the instrument cluster. The indicator remains controlled and illuminated by the cluster until a valid lamp-on or lamp-off message is received from the PCM.

MIL illumination

In many instances, emissions systems must fail diagnostic tests more than once before the PCM illuminates the MIL. These tests are know as 'two trip monitors.' Other tests that turn the MIL lamp on after a single failure are known as 'one trip monitors.' A trip is defined as 'start the vehicle and operate it to meet the criteria necessary to run the given monitor.'

Certain conditions such as a loose or missing gas cap, poor fuel quality, etc. may illuminate the light after engine start. The vehicle should be serviced if the light stays on through several typical driving cycles. In most situations, the vehicle will drive normally and will not require towing.

Prolonged driving with the "Malfunction Indicator Light" or "Check Engine" light on could cause further damage to the emission control system. It could also affect fuel economy and driveability. The vehicle must be repaired before any emissions test can be performed.

If the light is flashing, severe catalytic converter damage and power loss will soon occur. Immediate service is required.

Retrieving codes:

Turn the ignition key until the digital odometer displays, repeat three times in succession and then back to "On" (On/Off, On/Off, On/Off, On). At the fourth "On" the odometer will be replaced with codes. If no codes are present then "Done" will appear.

Erasing codes:

After three good trips the MIL is extinguished and the Task Manager automatically switches the trip counter to a warm-up cycle counter. DTCs are automatically erased following 40 warm-up cycles if the component does not fail again.

DTCs can be erased anytime with a DRB III. Erasing the DTC with the DRB III erases all OBD II information. The DRB III automatically displays a warning that erasing the DTC will also erase all OBD II monitor data. This includes all counter information for warm-up cycles, trips and Freeze Frame.

OBD-II related links:

OBD-II Trouble Codes repair site

Facts About On-Board Diagnostic II Systems

The workings of OBD-II and its effect on modifications

OBD Scan Tools - Automotive Diagnostics

(M) Check Engine Lamp (MIL) will illuminate during engine operation if this Diagnostic Trouble Code was recorded (depending if required by CARB and/or EPA). MIL is displayed as an engine icon on the instrument cluster. (G) Generator Lamp Illuminated Chrysler uses ISO 9142-2 OBDII Communications Protocol

Scan Code

DRB Scan Tool Display

Description of Diagnostic Trouble Code

A Camshaft Position Actuator Circuit (Bank 1)

P0011

A Camshaft Position - Timing Over-Advanced or System Performance (Bank 1))

P0012

A Camshaft Position - Timing Over-Retarded (Bank 1)

P0013

B Camshaft Position - Actuator Circuit (Bank 1)

P0014

B Camshaft Position - Timing Over-Advanced or System Performance (Bank 1)

P0015

B Camshaft Position - Timing Over-Retarded (Bank 1)

P0016

Crankshaft/Camshaft Timing Misalignment

A rationality error has been detected for camshaft position out of phase with crankshaft.

P0020

A Camshaft Position Actuator Circuit (Bank 2)

P0021

A Camshaft Position - Timing Over-Advanced or System Performance (Bank 2)

P0022

A Camshaft Position - Timing Over-Retarded (Bank 2)

P0023

B Camshaft Position - Actuator Circuit (Bank 2)

P0024

B Camshaft Position - Timing Over-Advanced or System Performance (Bank 2)

P0025

B Camshaft Position - Timing Over-Retarded (Bank 2)

P0030

02 Sensor Heater Control Circuit (Bank 1 Sensor 1)

Shorted condition detected in the oxygen sensor heater element control feedback sense circuit.

P0031

02 Sensor Heater Control Circuit Low (Bank 1 Sensor 1)

Shorted low condition detected in the oxygen sensor 1/1 heater elementcontrol feedback sense circuit

P0032

02 Sensor Heater Control Circuit High (Bank 1 Sensor 1)

Shorted high condition detected in the oxygen sensor 1/1 heater element control feedback sense circuit

P0033

Turbo Charger Bypass Valve Control Circuit

P0034

Turbo Charger Bypass Valve Control Circuit Low

P0035

Turbo Charger Bypass Valve Control Circuit High

P0036

02 Sensor Heater Control Circuit (Bank 1 Sensor 2)

Shorted condition detected in the oxygen sensor heater element control feedback sense circuit.

P0037

02 Sensor Heater Control Circuit Low (Bank 1 Sensor 2)

Shorted condition detected in the oxygen sensor heater element control feedback sense circuit.

P0038

02 Sensor Heater Control Circuit High (Bank 1 Sensor 2)

Shorted condition detected in the oxygen sensor heater element control feedback sense circuit.

P0042

02 Sensor Heater Control Circuit (Bank 1 Sensor 3)

Shorted condition detected in the oxygen sensor heater element control feedback sense circuit.

P0043

02 Sensor Heater Control Circuit Low (Bank 1 Sensor 3)

Shorted condition detected in the oxygen sensor heater element control feedback sense circuit.

P0044

02 Sensor Heater Control Circuit High (Bank 1 Sensor 3)

Shorted condition detected in the oxygen sensor heater element control feedback sense circuit.

P0050

02 Sensor Heater Control Circuit (Bank 2 Sensor 1)

Shorted condition detected in the oxygen sensor heater element control feedback sense circuit.

P0051

02 Sensor Heater Control Circuit Low (Bank 2 Sensor 1)

Shorted condition detected in the oxygen sensor heater element control feedback sense circuit.

P0052

02 Sensor Heater Control Circuit High (Bank 2 Sensor 1)

Shorted condition detected in the oxygen sensor heater element control feedback sense circuit.

P0056

02 Sensor Heater Control Circuit (Bank 2 Sensor 2)

Shorted condition detected in the oxygen sensor heater element control feedback sense circuit.

P0057

02 Sensor Heater Control Circuit Low (Bank 2 Sensor 2)

Shorted condition detected in the oxygen sensor heater element control feedback sense circuit.

P0058

02 Sensor Heater Control Circuit High (Bank 2 Sensor 2)

Shorted condition detected in the oxygen sensor heater element control feedback sense circuit.

P0062

02 Sensor Heater Control Circuit High (Bank 2 Sensor 2)

Shorted condition detected in the oxygen sensor heater element control feedback sense circuit.

P0063

HO2S Heater Control Circuit Low (Bank 2 Sensor 3)

Shorted condition detected in the oxygen sensor heater element control feedback sense circuit.

P0064

HO2S Heater Control Circuit High (Bank 2 Sensor 3)

Shorted condition detected in the oxygen sensor heater element control feedback sense circuit.

P0065

Air Assisted Injector Control Range/Performance

P0066

Air Assisted Injector Control Circuit or Circuit Low

P0067

Air Assisted Injector Control Circuit High

P0068

Manifold Pressure/Throttle Position

Correlation MAP sensor signal does not correlate to throttle position sensor signal. Possible vacuum leak.

P0070

Ambient Temp Sensor Stuck

A rationality error has been detected in the ambient temperature sensor test.

P0071 (M)

Ambient Temp Sensor Performance

Ambient change less than 3° C in 200 miles.

P0072

Ambient Temp Sensor Low Input

Ambient temperature sensor input below the minimum acceptable voltage.

P0073

Ambient Temp Sensor High Input

Ambient temperature sensor input above the maximum acceptable voltage.

P0074

Ambient Air Temperature Sensor Circuit Intermittent

P0075

Intake Valve Control Solenoid Circuit (Bank 1)

P0076

Intake Valve Control Solenoid Circuit Low (Bank 1)

P0077

Intake Valve Control Solenoid Circuit High (Bank 1)

P0078

Exhaust Valve Control Solenoid Circuit (Bank 1)

P0079

Exhaust Valve Control Solenoid Circuit Low (Bank 1)

P0080

Exhaust Valve Control Solenoid Circuit High (Bank 1)

P0081

Intake valve Control Solenoid Circuit (Bank 2)

P0082

Intake Valve Control Solenoid Circuit Low (Bank 2)

P0083

Intake Valve Control Solenoid Circuit High (Bank 2)

P0084

Exhaust Valve Control Solenoid Circuit (Bank 2)

P0085

Exhaust Valve Control Solenoid Circuit Low (Bank 2)

P0086

Exhaust Valve Control Solenoid Circuit High (Bank 2)

Scan Code

DRB Scan Tool Display

Description of Diagnostic Trouble Code

P0100

Mass or Volume Air Flow Circuit

P0101

Mass or Volume Air Flow Circuit Range/Performance Problem

P0102

Mass or Volume Air Flow Circuit Low Input

P0103

Mass or Volume Air Flow Circuit High Input

P0104

Mass or Volume Air Flow Circuit Intermittent

P0105

Manifold Absolute Pressure/Barometric Pressure Circuit

P0106 (M)

Manifold Absolute Pressure/Barometric Pressure Circuit Range/Performance Problem

MAP sensor input voltage out of an acceptable range detected during reading of barometric pressure at key-on.

P0107 (M)

Manifold Absolute Pressure/Barometric Pressure Circuit Low Input

MAP sensor input below minimum acceptable voltage.

P0108 (M)

Manifold Absolute Pressure/Barometric Pressure Circuit High Input

MAP sensor input above maximum acceptable voltage.

P0109

Manifold Absolute Pressure/Barometric Pressure Circuit Intermittent

P0110

Intake Air Temp Sensor Stuck

A rationality error has been detected for the intake air temperature sensor.

P0111 (M)

Intake Air Temperature Circuit Range/Performance Problem

Air change less than 3° C in 200 miles.

P0112 (M)

Intake Air Temperature Circuit Low Input

Intake air (charge) temperature sensor input below the minimum acceptable voltage.

P0113 (M)

Intake Air Temperature Circuit High Input

Intake air (charge) temperature sensor input above the maximum acceptable voltage.

P0114

Intake Air Temperature Circuit Intermittent

P0115

Engine Coolant Temperature Circuit

P0116

Engine Coolant Temperature Circuit Range/Performance Problem

A rationality error has been detected in the coolant temperature sensor.

P0117 (M)

Engine Coolant Temperature Circuit Low Input

Engine coolant temperature sensor input below the minimum acceptable voltage.

P0118 (M)

Engine Coolant Temperature Circuit High Input

Engine coolant temperature sensor input above the maximum acceptable voltage.

P0119

Engine Coolant Temperature Circuit Intermittent

Engine coolant temperature sensor input above the maximum acceptable voltage.

P0120

Throttle/Pedal Position Sensor/Switch A Circuit

Engine coolant temperature sensor input above the maximum acceptable voltage.

P0121 (M)

Throttle/Pedal Position Sensor/Switch A Circuit Range/Performance Problem

TPS signal does not correlate to MAP sensor signal.

P0121 (M)

Accelerator Position Sensor (APPS)

APPS voltage input below the minimum acceptable voltage.

P0122 (M)

Throttle/Pedal Position Sensor/Switch A Circuit Low Input

Throttle position sensor input below the acceptable voltage range.

P0122 (M)

Accelerator Position Sensor (APPS) Signal Voltage Too Low

APPS voltage input below the minimum acceptable voltage.

P0123 (M)

Throttle/Pedal Position Sensor/Switch A Circuit Intermittent

Throttle position sensor input above the maximum acceptable voltage. Follow all appropriate diagnostics for the fault that is present. Prior to replacing parts, check all connectors between the speed control switch and the PCM for moisture Internally the PCM uses the same A/D (analog to digital) converter for TPS voltage as it does for the speed control switch sense. If the v-37 circuit has voltage bleed over from another source, a code of TPS Shorted to voltage may be set in the PCM. The DN model equipped with rear heat option, has an external water pump to circulate coolant to the rear heater. If you find coolant in the bulkhead connector, the likely cause would be a leaking coolant pump. Pump should be replaced if found leaking. If the code sets when the A/C is turned on go right to the bulk head connector and check for moisture. Check for a shorted clock spring causing the speed control 5 volt feed to be shorted to power.

P0123 (M)

Accelerator Position Sensor (APPS) Signal Voltage Too High

APPS voltage input above the maximum acceptable voltage.

P0125 (M)

Insufficient Coolant Temperature for Closed Loop Fuel Control

Time to enter Closed Loop Operation (Fuel Control) is excessive.

P0125 (M)

Engine is Cold Too Long

Engine does not reach operating temperature.

P0126

Insufficient Coolant Temperature for Stable Operation

P0127

Intake Air Temperature Too High

P0128

Coolant Thermostat (Coolant Temperature Below Thermostat Regulating Temperature)

A rationality error has been detected for the thermostat.

P0129

Barometic Pressure Out-of-Range low

MAP sensor input voltage out of an acceptable range detected during reading of barometric pressure.

P0130

O2 Sensor Circuit (Bank 1 Sensor 1)

An open or shorted condition detected in the ASD or CNG shutoff relay control ckt.

P0131 (M)

O2 Sensor Circuit Low Voltage (Bank 1 Sensor 1)

Oxygen sensor input voltage maintained below normal operating range.

P0132 (M)

O2 Sensor Circuit High Voltage (Bank 1 Sensor 1)

Oxygen sensor input voltage maintained above normal operating range.

P0133 (M)

O2 Sensor Circuit Slow Response (Bank 1 Sensor 1)

Oxygen sensor response slower than minimum required switching frequency.

P0134 (M)

O2 Sensor Circuit No Activity Detected (Bank 1 Sensor 1)

Neither rich or lean condition is detected from the oxygen sensor input.

P0135 (M)

O2 Sensor Heater Circuit (Bank 1 Sensor 1)

Oxygen sensor heater element malfunction.

P0136

O2 Sensor Circuit Malfunction (Bank 1 Sensor 2)

An open or shorted condition detected in the ASD or CNG shutoff relay control ckt.

P0137 (M)

O2 Sensor Circuit Low Voltage (Bank 1 Sensor 2)

Oxygen sensor input voltage maintained below normal operating range.

P0138 (M)

O2 Sensor Circuit High Voltage (Bank 1 Sensor 2)

Oxygen sensor input voltage maintained above normal operating range.

P0139 (M)

OS Sensor Circuit Slow Response (Bank 1 Sensor 2)

Oxygen sensor response not as expected.

P0140 (M)

O2 Sensor Circuit No Activity Detected (Bank 1 Sensor 2)

Neither rich or lean condition is detected from the oxygen sensor.

P0141 (M)

O2 Sensor Heater Circuit (Bank 1 Sensor 2)

Oxygen sensor heater element malfunction. O2 sensor voltage greater than 3 volts for 60 to 240 seconds.

P0142 (M)

Sensor Circuit Malfunction (Bank 1 Sensor 3)

Oxygen sensor heater element malfunction.

P0143

O2 Sensor Circuit Low Voltage (Bank 1 Sensor 3)

Oxygen sensor input voltage maintained below normal operating range.

P0144

O2 Sensor Circuit High Voltage (Bank 1 Sensor 3)

Oxygen sensor input voltage maintained above normal operating range.

P0145

O2 Sensor Circuit Slow Response (Bank 1 Sensor 3)

Oxygen sensor response slower than minimum required switching frequency.

P0146

O2 Sensor Circuit No Activity Detected (Bank 1 Sensor 3)

Neither rich or lean condition is detected from the oxygen sensor.

P0147

O2 Sensor Heater Circuit (Bank 1 Sensor 3)

Oxygen sensor heater element malfunction.

P0148

Fuel Delivery Error

P0149

Fuel Timing Error

P0150

O2 Sensor Circuit (Bank 2 Sensor 1)

P0151 (M)

O2 Sensor Circuit Low Voltage (Bank 2 Sensor 1)

Oxygen sensor input voltage maintained below normal operating range.

P0152 (M)

O2 Sensor Circuit High Voltage (Bank 2 Sensor 1)

Oxygen sensor input voltage sustained above normal operating range.

P0153 (M)

O2 Sensor Circuit Slow Response (Bank 2 Sensor 1)

Oxygen sensor response slower than minimum required switching frequency.

P0154 (M)

O2 Sensor Circuit No Activity Detected (Bank 2 Sensor 1)

Neither rich or lean condition is detected from the oxygen sensor.

P0155 (M)

O2 Sensor Heater Circuit (Bank 2 Sensor 1)

Oxygen sensor heater element malfunction.

P0156 (M)

O2 Sensor Circuit Malfunction (Bank 2 Sensor2)

Oxygen sensor heater element malfunction.

P0157 (M)

O2 Sensor Circuit Low Voltage (Bank 2 Sensor 2)

Oxygen sensor input voltage maintained below normal operating range.

P0158 (M)

O2 Sensor Circuit High Voltage (Bank 2 Sensor 2)

Oxygen sensor input voltage maintained above normal operating range.

P0159

O2 Sensor Circuit Slow Response (Bank 2 Sensor 2)

Oxygen sensor response slower than minimum required switching frequency.

P0160 (M)

O2 Sensor Circuit No Activity Detected (Bank 2 Sensor 2)

Neither rich or lean condition is detected from the oxygen sensor.

P0161 (M)

O2 Sensor Heater Circuit (Bank 2 Sensor 2)

Oxygen sensor heater element malfunction. O2 sensor voltage greater than 3 volts for 60 to 240 seconds.

P0162 (M)

O2 Sensor Circuit Malfunction (Bank 2 Sensor 3)

Oxygen sensor heater element malfunction.

P0163 (M)

O2 Sensor Circuit Low Voltage (Bank 2 Sensor 3)

P0164 (M)

O2 Sensor Circuit High Voltage (Bank 2 Sensor3)

P0165

O2 Sensor Circuit Slow Response (Bank 2 Sensor 3)

P0166

O2 Sensor Circuit No Activity Detected (Bank 2 Sensor 3)

P0167

OS Sensor Heater Circuit (Bank 2 Sensor 3)

P0168

Fuel Temperature Too High

P0169

Incorrect Fuel Composition

P0170

Fuel Trim (Bank 1)

P0171 (M)

System too Lean (Bank 1)

A lean air/fuel mixture has been indicated by an abnormally rich correction factor.

P0172 (M)

System too Rich (Bank 1)

A rich air/fuel mixture has been indicated by an abnormally lean correction factor. Was the fuel pressure checked with a DRBIII pressure transducer? Is the fuel pressure within specification with engine running at normal operating temperature? Verify the correct DRBIII PEP module pressure transducer is being used It is critical when reading pressures with the DRBIII PEP module pressure transducers that the proper transducer is being used. A too high of value transducer will cause inaccurate readings. It is also critical that the DRBIII and pressure transducer is zeroed out before taking a reading.Repair or replace any fuel system malfunctioning components.

P0173 (M)

Fuel Trim Malfunction (Bank 2)

P0174 (M)

System too Lean (Bank 2)

A lean air/fuel mixture has been indicated by an abnormally rich correction factor.

P0175 (M)

System too Rich (Bank 2)

A rich air/fuel mixture has been indicated by an abnormally lean correction factor.

P0176

Fuel Composition Sensor Circuit

No calibration voltage present from flex fuel sensor.

P0177

Fuel Composition Sensor Circuit Range/Performance

P0178

Fuel Composition Sensor Circuit Low Input

Flex fuel sensor input below minimum acceptable voltage.

P0178

Water in Fuel Light—Water In Fuel Sensor Voltage Too Low

Loss of water-in-fuel circuit or sensor.

P0179

Fuel Composition Sensor Circuit High Input

Flex fuel sensor input above maximum acceptable voltage.

P0180

Fuel Temperature Sensor A Circuit

P0181

Fuel Temperature Sensor A Circuit Range/Performance

P0182 (M)

Fuel Temperature Sensor A Circuit Low Input

Compressed natural gas temperature sensor voltage below acceptable voltage

P0183 (M)

Fuel Temperature Sensor A Circuit High Input

Compressed natural gas temperature sensor voltage above acceptable voltage

P0184

Fuel Temperature Sensor A Circuit Intermittent

P0185

Fuel Temperature Sensor B Circuit

P0186

Fuel Temperature Sensor B Circuit Range/Performance

P0187

Fuel Temperature Sensor B Circuit Low Input

P0188

Fuel Temperature Sensor B Circuit High Input

P0189

Fuel Temperature Sensor B Circuit Intermittent

P0190

Fuel Rail Pressure Sensor Circuit

P0191

Fuel Rail Pressure Sensor Circuit Range/Performance

P0192

Fuel Rail Pressure Sensor Circuit Low Input

P0193

Fuel Rail Pressure Sensor Circuit High Input

P0194

Fuel Rail Pressure Sensor Circuit Intermittent

P0195

Engine Oil Temperature Sensor

P0196

Engine Oil Temperature Sensor Range/Performance

P0197

Engine Oil Temperature Sensor Low

P0198

Engine Oil Temperature Sensor High

P0199

Engine Oil Temperature Sensor Intermittent