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 1--Contains general information regarding fuel delivery and basic engine operating conditions.
    • Engine Data 2--Contains general information regarding IC, KS, A/C, and basic engine operating conditions.
    • Catalyst Data--Contains information specific to the TWC diagnostics and parameters required to verify proper TWC system operation.
    •  EGR Data--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 Data--Contains information specific to the Evaporative Emissions (EVAP) control system. Also displays parameters required to verify proper EVAP system operation.
    • HO2S Data--Contains information specific to the Heated Oxygen Sensor diagnostics and parameters required to verify proper HO2S operation.
    • Misfire Data--Contains information specific to the misfire diagnostics and parameters required to verify proper operation with regard to misfire.

For scan tool parameter definitions, refer to Engine Scan Tool Data Definitions .

Important: Use the Typical Scan Data Values only after the following conditions are met:

    • The Powertrain On-Board Diagnostic System Check has been completed.
    • The engine is idling unless checking a value at a specified RPM.
    • The lower radiator hose is hot.
    • The Throttle is closed unless checking a value at a specified RPM.
    • The vehicle is in PARK or NEUTRAL.
    • The vehicle is operating in Closed Loop.
    • The vehicle accessories are turned off.

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) Circuit Diagnosis

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

Catalyst

Misfire

Yes / No

No (Yes with A/C ON)

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

Actual EGR Position

Engine 1

Engine 2

EGR

Misfire

Percent

0%

Exhaust Gas Recirculation (EGR) System Description

Air/Fuel Ratio

Engine 1

Catalyst

HO2S

Ratio

14.2:1-14.7:1

DTC P0171 Fuel Trim System Lean

BARO

Engine 1

Engine 2

Catalyst

EVAP

EGR

kPa / Volts

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

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

Change Oil Lamp

Engine 2

On / Off

Off (On with 0% engine oil life remaining)

Powertrain Control Module Controlled Warning Lamps Description

Commanded A/C

Engine 2

Catalyst

Misfire

On / Off

Off (On with A/C compressor engaged)

Powertrain Control Module Controlled Air Conditioning Description

Commanded Fan 1/Commanded Fan 2

Engine 2

Catalyst

On / Off

Off (On with fans running)

Electric Cooling Fan Diagnosis

Commanded GEN

Engine 1

On / Off

On

DTC P0560 System Voltage

Cruise

Engine 1

Engaged / Disengaged

Disengaged

DTC P1554 Cruise Control Feedback Circuit

Cruise Inhibited

Engine 1

Yes / No

Yes

DTC P1585 Cruise Control Inhibit Output Circuit

Current Gear

Engine 1

1 / 2 / 3 / 4

1

Transaxle Diagnosis

Decel Fuel Mode

Engine 1

Engine 2

Catalyst

HO2S

Misfire

Active / Inactive

Inactive

Fuel Metering Modes of Operation

Desired EGR Position

Engine 1

Engine 2

EGR

Misfire

Percent

0%

Exhaust Gas Recirculation (EGR) System Description

Desired Idle Speed

Engine 1

Engine 2

Catalyst

EVAP

RPM

PCM commanded idle speed (varies with termperature)

Idle Air Control (IAC) System Diagnosis

ECT

All

°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 Valve Pintle Position

EGR

Volts

0.14-1.0 Volts

Exhaust Gas Recirculation (EGR) System Description

EGR Duty Cycle

EGR

Percent

0%

Exhaust Gas Recirculation (EGR) System Description

EGR Feedback

EGR

Volts

0.14-1.0 Volts

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%

Exhaust Gas Recirculation (EGR) System Description

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

Catalyst

EVAP

Hr: Min: Sec

Depends on time since startup

--

Engine Speed

All

RPM

± 100 RPM from Desired Idle Speed

--

EVAP Cansiter Purge

EVAP

HO2S

Percent

0% - 25% (varies)

Evaporative Emission Control System Diagnosis

EVAP Fault History

EVAP

No Fault

Excess Vacuum

Purge Valve Leak

Small Leak

Weak Vacuum

No Fault

Evaporative Emission Control System Diagnosis

EVAP Vent Sol.

EVAP

Open / Closed

Open

Evaporative Emission Control System Diagnosis

Fuel Level

EVAP

Percent

0%-25% (varies)

Fuel Level Sensor Diagnosis

Fuel Pump

Engine 2

On / Off

On

Fuel Metering System Component Description

Fuel Pump Speed (VIN 1)

Engine 2

Normal / High

Normal

Fuel Metering System Component Description

Fuel Tank Pressure

EVAP

In. H2O

Volts

0

Evaporative Emission Control System Diagnosis

Fuel Trim Cell

Engine 1

Misfire

Cell #

0

DTC P0172 Fuel Trim System Rich

Fuel Trim Learn

Engine 1

Catalyst-

Disabled / Enabled

Enabled

--

Generator Lamp

Engine 2

On / Off

Off

DTC P1637

Generator PWM

Engine 2

Percent

Varies

Charging System

HO2S Sensor 1

Engine 1

HO2S

Not Ready / Ready

Ready

DTC P0137 HO2S Circuit Low Voltage Sensor 2

HO2S Sensor 1

Engine 1

Catalyst

HO2S

Millivolts

0-1000 constantly varying

Information Sensors/Switches Description

HO2S Sensor 2

Engine 1

Catalyst

HO2S

Millivolts

0-1000 constantly varying

Information Sensors/Switches Description

HO2S Warm Up Time Sensor 1 / HO2S Warm Up Time Sensor 2

HO2S

Min: Sec

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

DTC P0135 HO2S Heater Performance Sensor 1

HO2S XCounts

HO2S

Counts

Varies

--

Hot Lamp

Engine 2

On / Off

Off

DTC P1673 Engine Hot Lamp Control Circuit

IAC Position

Engine 1

Engine 2

Catalyst

EGR

Misfire

Counts

10-40

Idle Air Control (IAC) System Diagnosis

IAT

Engine 1

Engine 2

Catalyst

EVAP

HO2S

°C, °F

Varies with ambient air termperature

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

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 Description

Injector Pulse Width

Engine 1

Catalyst

Milliseconds

1.5-3.5 (varies with engine load

--

Knock Retard

Engine 2

Degrees

0 degrees

Knock Sensor (KS) System Description

Long Term FT

Engine 1

Misfire

Percent

-10%-10%

DTC P0172 Fuel Trim System Rich

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

DTC P1672 Low Engine Oil Lamp Control Circuit

MAF

Engine 1

Engine 2

Catalyst

HO2S

g/s

3-6 g/s at idle

13-16 g/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

EVAP

EGR

kPa / Volts

29-48 kpa / 1-2 volts (Depends on engine load and barometric pressure)

Information Sensors/Switches Description

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 (Primary / Secondary)

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 FT

Engine 1

Catalyst

Misfire

Percent

-10%-10%

DTC P0172 Fuel Trim System Rich

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 P0135 HO2S Heater Performance Sensor 1

Start Up IAT

EVAP

HO2S

°C, °F

Depends on engine ambient temperature at time of startup

DTC P0135 HO2S Heater Performance Sensor 1

Supercharger Boost

Engine 2

Percent

100%

Boost Control System Description

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

Catalyst

EGR

HO2S

Misfire

Percent

0%

Information Sensors/Switches Description

TP Sensor

Engine 1

Volts

0.20-0.74

Information Sensors/Switches Description

Traction Control

Engine 2

Active / Inactive

Inactive

ABS/TCS

Traction Control Desired Torque

Engine 2

Percent

80%-95%

ABS/TCS

Traction Control Torque

Engine 2

Percent

5%-20% (Varies with load)

ABS/TCS

Transmission Range

Engine 2

Catalyst

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

Park

--

TR Switch P / A / B / C

Engine 2

High / Low

Low / Low / High / High

--

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

Transaxle Diagnosis

VTD Fuel Disable

Engine 2

Inactive / Active

Inactive

DTC P1629