On Board Diagnostic (OBD) System Check
The Powertrain OBD System Check is an organized approach to identifying a problem that is created by an electronic engine control system malfunction. The OBD system check is the starting point for any driveability complaint diagnosis. This directs the service technician to the next logical step in diagnosing the complaint. Keep the following special considerations in mind while making the OBD system check :
Blocking Drive Wheels
Block the vehicle drive wheels and set the emergency brake while checking the system.
Cold Oxygen Sensor (O2S 1)
On certain engines, the Oxygen Sensor (O2S 1) may cool down after only a short period of operation at idle. This may cause the system to go into an Open Loop operation. Run the engine at part throttle several minutes and accelerate the engine from idle to part throttle a few times in order to restore a Closed Loop operation.
Notice: Do not use a scan tool that displays faulty data. Report the scan tool problem to the manufacturer. Use of a faulty scan tool can result in misdiagnosis and unnecessary parts replacement.
Only the parameters listed below are used in this manual for diagnosis. If a scan tool reads other parameters, General Motors does not recommend these values for use in the diagnosis. For more description on the values and use of the scan tool to diagnose the PCM inputs, refer to the applicable diagnostic section. If all of the values are within the illustrated ranges, refer to Symptoms.
At Idle/Upper Radiator/Closed Throttle/Park or Neutral/Closed Loop/Acc. OFF | ||
|---|---|---|
Scan Tool Parameter | Units Displayed | Typical Data Value |
Engine Speed | RPM | ±100 RPM from the desired RPM |
Desired Idle | RPM | PCM idle command (varies with calibration) |
ECT | C-F | 85°-115°C (185°-239°F) (varies with the coolant temperature) |
IAT | C-F | 10°-80°C (50°-176°F) (varies with under hood temperature) |
MAP | kPa, V | 1-3 volts (varies with the vacuum and the BARO pressure |
BARO | kPa, V | 3-5 volts (varies with the altitude and the BARO pressure |
TP Sensor | Volts | 0.200-0.900V (up to 5.0 at wide open throttle) |
TP Angle | % | 0% (up to 100% at wide open throttle) |
O2S 1 | mV | 1-1000 and varying |
HO2S 2 | mV | 1-1000 and varying |
Fuel Trim Cell | Cell Number | 18-21 at idle (varies with the air flow, RPM, P/N, and A/C) |
Fuel Trim Index | Counts, % | 58-198 (varies) (100% to 100%) (varies) |
Short Term FT | Counts, % | 58-198 (varies) (-100% to 100%) (varies) |
Long Term FT | Counts, % | 58-198 (varies) (-100% to 100%) (varies) |
Short Term FT Average | Counts, % | 58-198 (varies) (-100% to 100%) (varies) |
Long Term FT Average | Counts, % | 58-198 (varies) (-100% to 100%) (varies) |
Low Octane Fuel Spark Modifier | Degrees | Varies with fuel |
Spark | Degrees | Varies |
KS Retard | Degrees | 0 |
KS Noise Channel | Yes/No | No |
KS Active Counter | 0-255 Counts | 35-50 |
Med. Resolution Resync Counter | 0-255 Counts | 0 |
CKP Act. Counter (7x Reference) | 0-255 Counts | 0-255 - Increments while cranking or running |
CMP Act. Counter | 0-255 Counts | 0-255 - Increments while cranking or running |
Med. Resolution Engine Sync | Yes/No | Yes |
CMP Resync Counter | 0-255 Counts | 0 |
Purge Lrn. Mem. | Counts | 1.00 |
EVAP Sol. | % | 0-100% |
EVAP Vent Sol. | On/Off | Off |
IAC Position | Counts | 5-60 |
Loop Status | Open/Closed | Closed |
Engine Speed | RPM | ±100 RPM from the desired RPM |
FC Relay | On/Off | Off |
Ignition Volts | Volts | 12.0-15.0V |
GEN F Terminal | % | 0-100% (varies) |
GEN L Terminal | Active/Inactive | Inactive |
TCC Brake Switch | Off/On | Off |
Power Enrichment | Active/Inactive | Inactive |
Calc. Air Flow | g/s | Varies |
LOAD (2.4L Engine) | % | 15-21% (16-29% @ 2500 Rpm) |
LOAD (2.2L Engine) | % | 22-26% (19-25% @ 2500 Rpm) |
Engine Run Time | Seconds | Varies (since start up) |
# of Current DTCs | # | 0 |
At Idle/Upper Radiator/Closed Throttle/Park or Neutral/Closed Loop/Acc. OFF | ||
|---|---|---|
Scan Tool Parameter | Units Displayed | Typical Data Value |
Engine Speed | RPM | ±100 RPM from the desired RPM |
Desired Idle | RPM | PCM idle command (varies with calibration) |
ECT | °C-°F | 85°-115°C (185°-239°F)(varies with the coolant temperature) |
IAT | °C-°F | 10°- 80°C (50°- 176°F)(varies with under hood temperature) |
MAP | kPa, V | 1-3 volts (varies with the vacuum and the BARO pressure |
BARO | kPa, V | 3-5 volts (varies with the altitude and the BARO pressure |
TP Sensor | Volts | 0.200-0.900V (up to 5.0 at wide open throttle) |
TP Angle | % | 0% (up to 100% at wide open throttle) |
Total Misfire | 0-255 Counts | 0 (increases with misfires) |
Air Fuel Ratio | Ratio | 14.7:1 (varies) |
Base PWM Cyl. 1 | mS | 1-4 varies |
Base PWM Cyl. 2 | mS | 1-4 varies |
Base PWM Cyl. 3 | mS | 1-4 varies |
Base PWM Cyl. 4 | mS | 1-4 varies |
Engine Oil Level | OK/Low | OK (Low with the low oil level) |
Engine Oil Pres. | OK/Low | OK (Low with low oil pressure) |
A/C Request | Yes/No | No |
A/C Relay | Off/On | Off (On with the A/C request) |
A/C High side | Volts/PSI | 0-5.0 Volts/0-450 PSI (varies with the refrigerant pressure) |
Stepper Cruise | Enabled/Disabled | Disabled |
Cruise Engaged | Yes/No | No |
Output Driver 1 Short | 00000000 | 00000000 (A 1 appears with a short to voltage) |
Output Driver 1 Open | 00000000 | 00000000 (A 1 appears with a short to ground or open) |
Output Driver 2 Short | 00000000 | 00000000 (A 1 appears with a short to voltage) |
Output Driver 2 Open | 00000000 | 00000000 (A 1 appears with a short to ground or open) |
TR Switch (P) | Low/High | Low (Auto trans only) (Park only) |
TR Switch (A) | Low/High | Low (Auto trans only) (Park only) |
TR Switch (B) | Low/High | High (Auto trans only) (Park only) |
TR Switch (C) | Low/High | High (Auto trans only) (Park only) |
Trans. Range | Invalid/Low/Drive 2/Drive 3/Overdrive/Reverse/Park/Neutral | Park/Neutral (Auto trans only) |
MPH km/h | MPH and km/h | 0 |
At Idle/Upper Radiator/Closed Throttle/Park or Neutral/Closed Loop/Acc. OFF | ||
|---|---|---|
Scan Tool Parameter | Units Displayed | Typical Data Value |
Engine Speed | RPM | ±100 RPM from the desired RPM |
Desired Idle | RPM | PCM idle command (varies with the calibration) |
ECT | °C-°F | 85°-115°C (185°-239°F) (varies with the coolant temperature) |
IAT | °C-°F | 10°-80°C (50°-176°F) (varies with the underhood temperature) |
MAP | kPa, V | 1-3 volts (varies with the vacuum and the BARO pressure |
BARO | kPa, V | 3-5 volts (varies with the altitude and the BARO pressure) |
TP Sensor | volts | 0.200-0.900V (up to 5.0 at wide open throttle) |
TP Angle | % | 0% (up to 100% at wide open throttle) |
O2S 1 | mV | 1-1000 and varying |
HO2S 2 | mV | 1-1000 and varying |
IAC Position | Counts (steps) | 5-60 counts |
Fuel Trim Cell | Cell number | 18-21 at idle (varies with the air flow, RPM, P/N, an A/C) |
Short Term FT | Counts, % | 58-198 (varies) -100% to 100% (varies) |
Long Term FT | Counts, % | 58-198 (varies) -100% to 100% (varies) |
Delta MAP Change | kPa | 0 or a negative number |
Decel EWMA | kPa | -3 or-4 |
Desired EGR Pos. | % | 0% |
Actual EGR Pos. | % | 0% |
EGR Trip Samples | # of Samples | -- |
EVAP Sol. | % | -- |
EVAP Vent Sol. | 0=Off/1=On | -- |
Fuel Level Sensor | Volts, % | -- |
Fuel Tank Vapor Pressure | Volts/Inches of H2O/seconds | -- |
Engine Run Time | Seconds | -- |
# of current DTCs | # | 0 |
At Idle/Upper Radiator/Closed Throttle/Park or Neutral/Closed Loop/Acc. OFF | ||
|---|---|---|
Scan Tool Parameter | Units Displayed | Typical Data Value |
Engine Speed | RPM | ±100 RPM from the desired RPM |
Desired Idle | RPM | PCM idle command (varies with calibration) |
ECT | °C -°F | 85°-115°C (185°-239°F) (varies with the coolant temperature) |
IAT | °C-°F | 10°-80°C (50°-176°F) (varies with under hood temperature) |
MAP | kPa, V | 1-3 volts (varies with the vacuum and the BARO pressure |
BARO | kPa, V | 3-5 volts (varies with the altitude and the BARO pressure |
TP Sensor | Volts | 0.200-0.900V (up to 5.0 at wide open throttle) |
TP Angle | % | 0% (up to 100% at wide open throttle) |
Misfire Cur. #1 | 0-255 Counts | 0 (increase with a misfire) |
Misfire Hist. #1 | 0-255 Counts | 0 (increase with a misfire) |
Misfire Cur. #2 | 0-255 Counts | 0 (increase with a misfire) |
Misfire Hist. #2 | 0-255 Counts | 0 (increase with a misfire) |
Misfire Cur. #3 | 0-255 Counts | 0 (increase with a misfire) |
Misfire Hist. #3 | 0-255 Counts | 0 (increase with a misfire) |
Misfire Cur. #4 | 0-255 Counts | 0 (increase with a misfire) |
Misfire Hist #4 | 0-255 Counts | 0 (increase with a misfire) |
Base PWM Cyl. 1 | mS | 1-4 varies |
Base PWM Cyl. 2 | mS | 1-4 varies |
Base PWM Cyl. 3 | mS | 1-4 varies |
Base PWM Cyl. 4 | mS | 1-4 varies |
Calc. Air Flow | g/s | Varies |
LOAD | % | 15-21% (16-29% @ 2500 Rpm) |
Total Misfire | 0-255 Counts | 0 (increase with a misfire |
Engine Run Time | Seconds | Varies (since start up) |
At Idle/Upper Radiator/Closed Throttle/Park or Neutral/Closed Loop/Acc. OFF | ||
|---|---|---|
Scan Tool Parameter | Units Displayed | Typical Data Value |
O2S 1 | mV | 1-1000 and varying |
HO2S s | mV | 1-1000 and varying |
Engine Speed | RPM | ±100 RPM from the desired RPM |
Desired Idle | RPM | PCM idle Command (varies with calibration) |
ECT | °C-°F | 85°-115°C (185°-239°F) (varies with the coolant temperature |
IAT | °C-°F | 10°-80°C (50°-176°F) (varies with the underhood temperature |
MAP | kPa, V | 1-3 volts (varies with the vacuum and the BARO pressure) |
BARO | kPa, V | 3-5 volts (varies with the altitude and the BARO pressure) |
TP Sensor | Volts | 0.200-0.900V (up to 5.0 at wide open throttle) |
TP Angle | % | 0% (up to 100% at wide open throttle |
Short Term FT | Counts, % | 58-198 (Varies) 100% to 100% (varies) |
Fuel Trim Cell | Cell # | 18-21 at idle (varies with air flow, RPM, P/N, an A/C) |
Fuel Trim Index | Counts,% | 8-198 (Varies) 100% to 100% (varies) |
Short Term FT Average | Counts, % | 8-198 (Varies) 100% to 100% (varies) |
Long Term FT | Counts, % | 8-198 (Varies) 100% to 100% (varies) |
Long Term FT Average | Counts, % | 8-198 (Varies) 100% to 100% (varies) |
Lean/Rich Transition | 0-255 Counts | 0 |
Rich/Lean Transition | 0-255 Counts | 0 |
Lean/Rich Average | mS | 0 |
Rich/Lean Average | mS | 0 |
Lean/Rich to Rich/Lean Ratio Sen. 1 | Ratio | Varies |
Calc. Air Flow | g/s | Varies |
LOAD ( 2.4L Engine) | % | 15-21% (16-29% @ 2500 Rpm) |
LOAD ( 2.2L Engine) | % | 22-26% (19-25% @ 2500 Rpm) |
Loop Status | Open/Closed | Closed |
Engine Run Time | Seconds | Varies (since start up) |
At Idle/Upper Radiator/Closed Throttle/Park or Neutral/Closed Loop/Acc. OFF | ||
|---|---|---|
Scan Tool Parameter | Units Displayed | Typical Data Value |
DTC Freeze Frame | # | DTC # |
Scan Tool Parameter | Units Displayed | Typical Data Value |
Air/Fuel Ratio | Ratio | Varies |
Calc. Air Flow | g/S | Varies |
ECT | °C-°F | Varies |
BARO | kPa, V | Varies |
Base PWM Cyl. 1 | mS | Varies |
MAP | kPa, V | Varies |
Short Term FT | Counts, % | Varies |
Long Term FT | Counts, % | Varies |
Loop Status | Open/Closed | Varies |
MPH | MPH and km/h | Varies |
Load (2.4L Engine) | % | 15-21% (16-29% @ 2500 Rpm) |
Load (2.2L Engine) | % | 22-26% (19-25% @ 2500 Rpm) |
TP Angle | % | Varies |
Engine Speed | RPM | Varies |
