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 unnecessary 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 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

    • CATALYST - Contains information specific to the TWC diagnostics and parameters required to verify proper TWC system operation.
    • 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.
    • 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

Powertrain Control Module Controlled Air Conditioning

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 Request

Engine 2

Yes / No

No (Yes with A/C ON)

Powertrain Control Module Controlled Air Conditioning

Actual EGR Position

Engine 1

Engine 2

EGR

Misfire

Percent

0%

DTC P1406 Exhaust Gas Recirculation (EGR) Position Sensor Performance

Air/Fuel Ratio

Engine 1

Catalyst

Ratio

14.2:1 - 14.7:1

Fuel Metering Modes of Operation

BARO

Engine 1

Engine 2

EGR

kPa / Volts

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

Information Sensors

Clutch Pedal Switch

Engine 2

Applied / Released

Released

DTC P0704 Clutch Switch Circuit

Commanded A/C

Engine 2

On / Off

Off (On with A/C compressor engaged)

Powertrain Control Module Controlled Air Conditioning

Commanded Fan 1/Commanded Fan 2

Engine 2

On / Off

Off (On with fans running)

Electric Cooling Fan

Commanded Gen

Engine 1

On / Off

On

DTC P0560 System Voltage

Cruise Engaged

Engine 1

Engaged/Disengaged

No

DTC P1554 Cruise Control Feedback Circuit

Cruise Inhibited

Engine 1

Yes / No

Yes

DTC P1554 Cruise Control Feedback Circuit

Current Gear

Engine 1

EGR

1 / 2 / 3 / 4

1

Automatic Transmission Diagnosis

Decel Fuel Mode

Engine 1

EGR

Catalyst

Misfire

Active / Inactive

Inactive

Fuel Metering Modes of Operation

Desired EGR Position

Engine 1

Engine 2

EGR

Misfire

Percent

0%

DTC P1406 Exhaust Gas Recirculation (EGR) Position Sensor Performance

Desired Idle Speed

Engine 1

Engine 2

EGR

RPM

PCM commanded idle speed (varies with temperature).

Idle Air Control (IAC) System Check

ECT

Engine 1

, Engine 2

EGR

Catalyst

HO2S

Misfire

°C, °F

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

Information Sensors

EGR Closed Valve Pintle Position

EGR

Volts

0.14-1.0 volt

DTC P1406 Exhaust Gas Recirculation (EGR) Position Sensor Performance

EGR Duty Cycle

EGR

Percent

0%

DTC P1406 Exhaust Gas Recirculation (EGR) Position Sensor Performance

EGR Feedback

EGR

Volts

0.14 - 1.0 volt

DTC P1406 Exhaust Gas Recirculation (EGR) Position Sensor Performance

EGR Position Error

EGR

Percent

0% - 100%

DTC P1406 Exhaust Gas Recirculation (EGR) Position Sensor Performance

EGR Flow Test Count

EGR

Counts

0 - 10

DTC P1406 Exhaust Gas Recirculation (EGR) Position Sensor Performance

Engine Load

Engine 2

Catalyst

Misfire

Percent

2% - 5% at idle

7% - 10% at 2500 RPM

--

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 Speed

--

EVAP Canister Purge

EVAP

Percent

0% - 25% (varies)

Evaporative Emission Control System

EVAP Vacuum Switch

EVAP

Purge / No Purge

No Purge (Purge if over 25% EVAP Purge PWM is commanded).

Evaporative Emission Control System

Fuel Pump

Engine 2

On / Off

On

Fuel Supply Components

Fuel Trim Cell

Engine 1

Misfire

Cell #

0

DTC P0172 Fuel Trim System Rich Bank 1

Generator Lamp

Engine 2

On / Off

Off

Powertrain Control Module Controlled Warning Lamps

HO2S Bank 1 Sensor 1 / HO2S Bank 2 Sensor 1

Engine 1

HO2S

Not Ready / Ready

Ready

Information Sensors

HO2S Bank 1 Sensor 1 / HO2S Bank 2 Sensor 1

Engine 1

HO2S

millivolts

0 - 1000, constantly varying

Information Sensors

HO2S Bank 1 Sensor 2 / HO2S Bank 1 Sensor 3

Engine 1

Catalyst

HO2S

mIllivolts

0 - 1000,varies

Information Sensors

HO2S Warm-Up Bank 1 Sensor 1 / Bank 2 Sensor 1 / Bank 1 Sensor 2 / Bank 1 Sensor 3

HO2S

Min: Sec

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

Information Sensors

HO2S XCounts Bank 1 / HO2S XCounts Bank 2

HO2S

Counts

Varies

--

IAC Position

Engine 1

Engine 2

EGR

Catalyst

Misfire

Counts

10 - 40

Idle Air Control (IAC) System Check

IAT

Engine 1

Engine 2

EVAP

Catalyst

HO2S

°C, °F

Varies with ambient air temperature.

Information Sensors

Ignition 1

Engine 1

Engine 2

EGR

HO2S

Volts

13 (Varies)

DTC P0560 System Voltage

Ignition Mode

Engine 2

IC / Bypass

IC

Electronic Ignition (EI) System

Injector Pulse Width

Engine 1

milliseconds

1.5 - 3.5 (Varies with engine load)

--

Knock Retard

Engine 2

Degrees

Knock Sensor (KS) System

KS Active Counter

Engine 2

Counts

Varies, should not increment continuously

Knock Sensor (KS) System

KS Minimum Learned Noise

Engine 2

Volts

0.1 - 3.0 (varies)

Knock Sensor (KS) System

KS Noise Channel

Engine 2

Volts

0.1 - 3.0 (varies)

Knock Sensor (KS) System

Long Term Fuel Trim BN1

Engine 1

Misfire

Percent

-10% - 10%

DTC P0171 Fuel Trim System Lean Bank 1

Long Term Fuel Trim BN2

Engine 1

Misfire

Percent

-10% - 10%

DTC P0174 Fuel Trim System Lean Bank 2

Loop Status

Engine 1

Catalyst

HO2S

Misfire

Open / Closed

Closed

Fuel Metering Modes of Operation

MAF

Engine 1

Engine 2

EVAP

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

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).

Information Sensors

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 - 6

DTC P0300 Engine Misfire Detected

Misfiring Cylinder

Misfire

Cylinder # / 0

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 BN1

Engine 1

Misfire

Percent

-10% - 10%

DTC P0171 Fuel Trim System Lean Bank 1

Short Term Fuel Trim BN2

Engine 1

Misfire

Percent

-10% - 10%

DTC P0174 Fuel Trim System Lean Bank 2

Spark

Engine 2

Degrees

-20° (varies)

Electronic Ignition (EI) System

Start Up ECT

EVAP

HO2S

°C, °F

Depends on engine coolant temperature at time of startup

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

Start Up IAT

EVAP

HO2S

°C, °F

Depends on intake air temperature at time of startup

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

Throttle at Idle

Engine 1

Yes / No

Yes

DTC P0123 Throttle Position (TP) Sensor Circuit High Voltage

Total Misfire Current Count

Misfire

Counts

0 - 255

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 P0123 Throttle Position (TP) Sensor Circuit High Voltage

TP Sensor

Engine 1

Volts

0.20 - 0.74

Information Sensors

TR Switch A / B / C

Engine 2

Low/High

Varies depending on gear selected

Automatic Transmission Diagnosis

Trans Range

Engine 2

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

Park

Automatic Transmission Diagnosis

TWC Diagnostic

Catalyst

Enabled / Disabled

Enabled

DTC P0420 Catalyst System Low Efficiency

TWC Monitor Test Counter

Catalyst

Counts

0

DTC P0420 Catalyst System Low Efficiency

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

Automatic Transmission Diagnosis

VTD Fuel Disable

Engine 2

Active / Inactive

Inactive

DTC P1629 Theft Deterrent Fuel Enable Signal Not Received