GM Service Manual Online
For 1990-2009 cars only

Use the Typical Scan Data Values table only after the Powertrain On-Board Diagnostic System Check has been completed, no DTC(s) were noted and you have determined the on-board diagnostics are functioning properly. Scan tool values from a properly running engine may be used for comparison with the engine you are diagnosing. The Typical Scan Data values represent values that would be seen on a normally running engine.

Important: A scan tool that displays faulty data should not be used, and the problem should be reported to the scan tool manufacturer. Use of a faulty scan tool can result in misdiagnosis and unecessary parts replacement.

Only the parameters listed below are referred to in this service manual for use in diagnosis. For further information on using the scan tool to diagnose the PCM and related sensors, refer to the applicable reference section listed below. If all values are within the typical range described below, refer to Symptoms section for diagnosis. The Typical Scan Data Values table contains all the parameters included in the following data lists arranged in alphabetical order:

Engine Idling, Fully Warmed-Up, Closed Loop - Park or Neutral

Engine Data

    • ENG 1- Contains general information regarding fuel delivery and basic engine operating conditions.
    • ENG 2 - Contains general information regarding IC, KS, A/C, and basic engine operating conditions.
    • EGR - Contains information specific to the Exhaust Gas Recirculation system flow diagnostics and the EGR valve pintle position sensor diagnostics. Also displays parameters required to verify proper EGR system operation.
    • EVAP - Contains information specific to the EVAP system diagnostics. Also displays parameters required to verify proper EVAP system operation.
    • CATALYST - Contains information specific to the TWC diagnostics and parameters required to verify proper TWC system operation.
    • HO2S - Contains information specific to the Heated Oxygen Sensor diagnostics and parameters required to verify proper HO2S operation.
    • MISFIRE - Contains information specific to the misfire diagnostics and parameters required to verify proper operation with regard to misfire.

Engine Data

    • ENG 1- Contains general information regarding fuel delivery and basic engine operating conditions.
    • ENG 2 - Contains general information regarding IC, KS, A/C, and basic engine operating conditions.

Specific Engine Data

    • EGR - Contains information specific to the Exhaust Gas Recirculation system flow diagnostics and the EGR valve pintle position sensor diagnostics. Also displays parameters required to verify proper EGR system operation.
    • EVAP - Contains information specific to the EVAP system diagnostics. Also displays parameters required to verify proper EVAP system operation.
    • CATALYST - Contains information specific to the TWC diagnostics and parameters required to verify proper TWC system operation.
    • HO2S - Contains information specific to the Heated Oxygen Sensor diagnostics and parameters required to verify proper HO2S operation.
    • MISFIRE - Contains information specific to the misfire diagnostics and parameters required to verify proper operation with regard to misfire.

Typical Scan Tool Data Values

Scan Tool Parameter

Data List

Units Displayed

Typical Data Value

Reference

A/C High Side Pressure

Engine 2

Volts

Varies with refrigerant temperature

DTC P0530 Air Conditioning (A/C) Refrigerant Pressure Sensor Circuit

A/C Pressure Out Of Range

Engine 2

Yes / No

No (Yes with low or high A/C refrigerant pressure)

Powertrain Control Module Controlled Air Conditioning (A/C) Circuit Diagnosis

A/C Request

Engine 2

Yes / No

No (Yes with A/C ON)

Powertrain Control Module Controlled Air Conditioning (A/C) Circuit Diagnosis

Actual EGR Position

Engine 1

EGR

Misfire

Percent

0%

DTC P1404 Exhaust Gas Recirculation (EGR) Closed Position Performance

Air/Fuel Ratio

Engine 1

HO2S

Ratio

14.2:1 - 14.7:1

DTC P0171 Fuel Trim System Lean

BARO

Engine 1

Engine 2

EGR

EVAP

kPa / Volts

65 - 110 kPa (Depends on altitude and barometric pressure).

DTC P0107 Manifold Absolute Pressure (MAP) Sensor Circuit Low Voltage

Boost Solenoid PWM

Engine 2

Percent

100%

Boost Control System Diagnosis

Cam Signal Present

Misfire

Yes/No

Yes

Information Sensors/Switches Description

Commanded A/C

Engine 2

On / Off

Off (On with A/C compressor engaged)

Powertrain Control Module Controlled Air Conditioning (A/C) Circuit Diagnosis

Commanded Fan 1/Commanded Fan 2

Engine 2

On / Off

Off (On with fans running)

Electric Cooling Fan Diagnosis

Commanded Gen

Engine 1

On / Off

On when running

DTC P0560 System Voltage

Cruise

Engine 1

Engaged / Disengaged

Disengaged

DTC P1554 Cruise Control Feedback Circuit

Cruise Inhibited

Engine 1

Yes / No

Yes

DTC P1554 Cruise Control Feedback Circuit

Current Gear

Engine 1

1 / 2 /3 / 4

1

Functional Test

Decel Fuel Mode

Engine 1

Engine 2

Catalyst

HO2S

Misfire

Active / Inactive

Inactive

Fuel Metering Modes of Operation

Desired EGR Position

Engine 1

EGR

Misfire

Percent

0%

DTC P1404 Exhaust Gas Recirculation (EGR) Closed Position Performance

Desired Idle Speed

Engine 1

Engine 2

RPM

PCM commanded idle speed (varies with temperature).

Idle Air Control (IAC) System Diagnosis

ECT

Engine 1

Engine 2

EGR

EVAP

Catalyst

HO2S

Misfire

°C, °F

85°C - 105°C / 185°F - 220°F (varies with temperature).

DTC P0117 Engine Coolant Temperature (ECT) Sensor Circuit Low Voltage

EGR Closed Val. Pintle Position

EGR

Volts

0.14-1.0 volt

Evaporative Emission Control System Operation Description

EGR Duty Cycle

EGR

Percent

0%

Exhaust Gas Recirculation (EGR) System Description

EGR Feedback

EGR

Volts

0.14 - 1.0 volt

Exhaust Gas Recirculation (EGR) System Description

EGR Flow Test Count

EGR

Counts

0 - 10

DTC P0401 Exhaust Gas Recirculation (EGR) Flow Insufficient

EGR Position Error

EGR

Percent

0% - 9%

DTC P0404 Exhaust Gas Recirculation (EGR) Open Position Performance

Engine Hot Lamp

Engine 2

On/Off

Off

--

Engine Load

Engine 1

Engine 2

Catalyst

Misfire

Percent

2% - 5% at idle

7% - 10% at 2500 RPM

--

Engine Oil Level

Engine 2

Ok / Low

Ok

Engine Oil Level Sensor and/or Switch Diagnosis

Engine Oil Life

Engine 2

Percent

0%-100% (varies)

--

Engine Run Time

Engine 1

Engine 2

EVAP

Catalyst

Hr: Min: Sec

Depends on time since startup.

--

Engine Speed

Engine 1

Engine 2

EGR

EVAP

Catalyst

HO2S

Misfire

RPM

±100 RPM from Desired Idle

--

EVAP Canister Purge

EVAP

HO2S

Percent

0% - 25% (varies)

Evaporative Emission Control System Operation Description

EVAP Vent Solenoid

EVAP

Open/Closed

0% - 25% (varies)

Evaporative Emission Control System Operation Description

Fuel Pump

Engine 2

On / Off

On

Fuel Supply Component Description

Fuel Pump Speed

Engine 2

Normal / High

Normal

Fuel Supply Component Description

Fuel Tank Pressure

EVAP

In H20 Volts

0

Evaporative Emission Control System Diagnosis

Fuel Trim Cell

Engine 1

Cell #

0

DTC P0171 Fuel Trim System Lean

Fuel Trim Learn

Engine 1

Disabled / Enabled

Enabled

--

Generator PWM

Engine 2

Percent

Varies

Charging System Description

HO2S Sen. 1

Engine 1

HO2S

Not Ready / Ready

Ready

DTC P0135 HO2S Heater Performance Sensor 1

HO2S Sen. 1

Engine 1

HO2S

Catalyst

millivolts

0 - 1000, constantly varying

Information Sensors/Switches Description

HO2S Sen. 2

Engine 1

HO2S

Catalyst

mIllivolts

0 - 1000,varies

Information Sensors/Switches Description

HO2S Warm Up Sensor 1 / HO2S Warm Up Sensor 2

HO2S

Min: Sec

Depends on startup intake air temperature, startup engine coolant temperature, and time to HO2S activity.

Information Sensors/Switches Description

HO2S XCount

HO2S

Counts

Varies

--

IAC Position

Engine 1

Engine 2

EGR

Catalyst

Misfire

Counts

10 - 40

Idle Air Control (IAC) System Diagnosis

IAT

Engine 1

Engine 2

EVAP

Catalyst

HO2S

°C, °F

Varies with ambient air temperature.

DTC P0112 Intake Air Temperature (IAT) Sensor Circuit Low Voltage

Ignition 1

Engine 1

Engine 2

EGR

HO2S

Volts

13 (Varies)

Ignition Mode

Engine 2

IC / Bypass

IC

Electronic Ignition (EI) System Description

Injector Pulse Width

Engine 1

milliseconds

1.5 - 3.5 (Varies with engine load)

--

Knock Retard

Engine 2

Degrees

Knock Sensor (KS) System Description

Long Term Fuel Trim

Engine 1

Misfire

Percent

-10% - 10%

DTC P0171 Fuel Trim System Lean

Loop Status

Engine 1

Catalyst

HO2S

Misfire

Open / Closed

Closed

DTC P0125 Engine Coolant Temperature (ECT) Insufficient for Closed Loop Fuel Control

Low Oil Lamp

Engine 2

On / Off

Off

Powertrain Control Module Controlled Warning Lamps Diagnosis

MAF

Engine 1

Engine 2

Catalyst

HO2S

gm/s

3 - 6 gm/s at idle

13 - 16 gm/s at 2500 RPM (Depends on engine load and barometric pressure)

Information Sensors/Switches Description

MAF Frequency

Engine 1

Hz

1200 - 3000 (Depends on engine load and barometric pressure)

DTC P0102 Mass Air Flow (MAF) Sensor Circuit Low Frequency

MAP

Engine 1

Engine 2

EGR

EVAP

kPa / Volts

29 - 48 kPa / 1 - 2 Volts (Depends on engine load and barometric pressure).

DTC P0108 Manifold Absolute Pressure (MAP) Sensor Circuit High Voltage

MIL

Engine 2

On / Off

Off

Malfunction Indicator Lamp (MIL) Inoperative

Misfire Current Cylinder #

Misfire

Counts

0 - 4

DTC P0300 Engine Misfire Detected

Misfire History Cylinder #

Misfire

Counts

0

DTC P0300 Engine Misfire Detected

Misfiring Cylinder

Misfire

0 - 6

0

DTC P0300 Engine Misfire Detected

Power Enrichment

Engine 1

Engine 2

Catalyst

HO2S

Misfire

Active / Inactive

Inactive

Fuel Metering Modes of Operation

Rich/Lean

Engine 1

Rich / Lean

Constantly changing

Fuel Metering Modes of Operation

Short Term Fuel Trim

Engine 1

Misfire

Percent

-10% - 10%

DTC P0171 Fuel Trim System Lean

Spark

Engine 2

Degrees

20° (varies)

Electronic Ignition (EI) System Description

Start Up ECT

EVAP

HO2S

°C, °F

Depends on engine coolant temperature at time of startup

DTC P0117 Engine Coolant Temperature (ECT) Sensor Circuit Low Voltage

Start Up IAT

EVAP

HO2S

°C, °F

Depends on intake air temperature at time of startup

DTC P0113 Intake Air Temperature (IAT) Sensor Circuit High Voltage

Throttle at Idle

Engine 1

Yes / No

Yes

--

Total Misfire Current Count

Misfire

Counts

0 - 5

DTC P0300 Engine Misfire Detected

Total Misfire Failures Since First Fail

Misfire

Counts

0

DTC P0300 Engine Misfire Detected

Total Misfire Passes Since First Fail

Misfire

Counts

0

DTC P0300 Engine Misfire Detected

TP Angle

Engine 1

Engine 2

EGR

Catalyst

HO2S

Misfire

Percent

0%

DTC P0121 Throttle Position (TP) Sensor Performance

TP Sensor

Engine 1

Volts

0.20 - 0.74

DTC P0122 Throttle Position (TP) Sensor Circuit Low Voltage

Traction Control

Engine 2

Active / Inactive

Inactive

ABS Operation

Traction Control Desired Torque

Engine 2

Percent

100% at idle

ABS Operation

Traction Control Torque

Engine 2

Percent

83% at idle (Varies with load)

ABS Operation

Transmission Range

Engine 2

Park / Reverse / Neutral / Drive 4 / Drive 3 / Drive 2 / Low

Park

DTC P0706 Trans Range Switch Performance

TR Switch P / A / B / C

Engine 2

High / Low

Low / Low / High / High

DTC P0705 Trans Range Switch Circuit

TWC Protection

Engine 1

Engine 2

Catalyst

HO2S

Misfire

Active / Inactive

Inactive

Fuel Metering Modes of Operation

Vehicle Speed

Engine 1

Engine 2

EGR

Catalyst

Misfire

MPH, Km/h

0

Functional Test

VTD Fuel Disable

Engine 2

Active / Inactive

Inactive

DTC P1629 Theft Deterrent Fuel Enable Signal Not Received

3 X Crank Sensor

Misfire

RPM

Varies with engine RPM

Information Sensors/Switches Description

18 X Crank Sensor

Misfire

RPM

Varies with engine RPM

Information Sensors/Switches Description