GM Service Manual Online
For 1990-2009 cars only

Use the Typical Scan Data Values table only after the Powertrain On Board Diagnostic (OBD) System Check has been completed, no DTCs 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 in engine controls 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.
    • EVAP Data--Contains information specific to the evaporative emissions (EVAP) control system. Also displays parameters required to verify proper EVAP system operation.
    • O2S--Contains the information that is specific to the oxygen sensor (O2S 1) and the rear heated oxygen sensor (HO2S 2) diagnosis and the data that is required in order to verify the proper operation of the sensors.
    • Misfire Data--Contains information specific to the misfire diagnostics and parameters required to verify proper operation with regard to misfire.
    • Output Driver Data--Contains information specific to the Output Driver System.

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

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

    • The Powertrain On Board Diagnostic (OBD) System Check has been completed.
    • The engine is idling unless checking a value at a specified RPM.
    • 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

A/C High Side Pressure

Engine 2

Volts

0-5.0 Volts

A/C High Side Pressure

Engine 2

kPa/psi

0-3100 kPa/0-450 psi (varies with the refrigerant pressure)

Another TWC Test Desired

O2S

Yes/No

No

A/C Relay

Engine 2

Output Driver

OFF/ON

OFF (ON with the A/C requested)

A/C Relay

Output Driver

OK/Fault/Invalid State

OK

A/C Request

Engine 2

Yes/No

No (Yes with A/C ON)

Adaptive Knock Retard

Engine 1

Degrees

0

Air/Fuel Ratio

Engine 2

Ratio

14.6:1 (varies)

BARO

Engine 1

Engine 2

EVAP

Misfire

O2S

kPa

65-104 (varies with the altitude and barometric pressure).

Base PWM Cyl. 1-4

Misfire

mS

1-4 varies

Calc. Air Flow

Engine 1

O2S

Misfire

g/s

Varies

Calc. Convertor Temp.

O2S

°C-°F

Varies with the engine Load

CKP Active Counter (7X Reference)

Engine 1

0-255 Counts

0-255--Increments while cranking or running

CMP Active Counter

Engine 1

0-255 Counts

0-255--Increments while cranking or running

CMP Resync Counter

Engine 1

0-255 Counts

0

Cruise

Engine 2

Enabled/Disable

Disable

Cruise

Engine 2

Engaged/Disengaged

Disengaged

Current TWC Test Complete

O2S

Yes/No

Yes

Desired Idle Speed

Engine 1

Engine 2

EVAP

Misfire

O2S

RPM

PCM commanded idle speed (varies with calibration).

Driver Module 1 Status

Output Driver

Enable/OFF High Volts/OFF High Temp/Invalid State

Enabled

Driver Module 2 Status

Output Driver

Enable/OFF High Volts/OFF High Temp/Invalid State

Enabled

Engine Coolant Low

Engine 2

OK/Low

OK (Low with low coolant level)

ECT

Engine 1

Engine 2

EVAP

Misfire

O2S

°C-°F

85°C-115°C/185°F-239°F (Varies with coolant temperature).

Engine Load

Engine 1

Misfire

%

11%-21%

16-29% at 2,500 RPM

Engine Oil Pressure

Engine 2

Low/OK

OK (Low with low oil pressure)

Engine Run Time

Engine 1

Engine 2

EVAP

Misfire

O2S

Hr:Min:Sec

Depends on time since startup.

Engine Speed

Engine 1

Engine 2

EVAP

Misfire

O2S

RPM

±100 RPM from Desired Idle

EVAP Canister Purge

Engine 1

EVAP

%

0%-100% (varies)

EVAP Purge Solenoid

Output Driver

OK/Fault/Invalid State

OK

EVAP Vent Solenoid

EVAP

Open/Closed

Open

EVAP Vent Solenoid

Output Driver

OK/Fault/Invalid State

OK

Fuel Level

EVAP

%

0-100% Depends on fuel level

Fuel Pump Relay Command

Engine 1

ON/OFF

ON

FC Relay 1

Engine 2

ON/OFF

OFF (Varies with fan request)

FC Relay 1

Output Driver

OK/Fault/Invalid State

OK

FC Relay 2

Engine 2

ON/OFF

OFF (Varies with fan request)

Fuel Tank Pressure

EVAP

mmHg/in H2O

Depends on Pressure/Vacuum

Fuel Tank Pressure

EVAP

Volts

Depends on Pressure/Vacuum

Fuel Trim Cell

Engine 1

EVAP

O2S

Cell number

18-21 at idle (Varies with the air flow, RPM P/N and A/C

Fuel Trim Index

O2S

%

58-198 (varies -100%-100%)

Generator L Terminal

Engine 1

Active/Inactive

Inactive

Generator PWM

Engine 1

%

0-100% (Varies)

HO2S 2

Engine 1

EVAP

O2S

mV

0-1000, constantly varying

IAC Position

Engine 1

EVAP

Counts

5-60

IAT

Engine 1

Engine 2

EVAP

Misfire

O2S

°C-°F

10°-80°C (50°-176°F varies with under hood temperature)

Ignition 1

Engine 1

Volts

12.0-15.0 Volts (Varies)

KS Noise Channel

Engine 1

Volts

Increments when knock is present

Knock Retard

Engine 1

Degrees

Lean/Rich Transition

O2S

0-255 Counts

0

Lean/Rich Average Time

O2S

mS

0

Long Term FT

Engine 1

EVAP

O2S

0% +/- 10%

58-198 (-100%- to 100% varies)

Loop Status

Engine 1

EVAP

Open/Closed

Closed

MAP

Engine 1

Engine 2

EVAP

Misfire

O2S

kPa

25-48 kPa

MAP

Engine 1

Engine 2

EVAP

Misfire

O2S

Volts

1-3 volts (Varies with the vacuum and BARO pressure)

MIL

Output Driver

OK/Fault/Invalid State

OK

Misfire Current #1-#4

Misfire

0-255 Counts

0 (increase with a misfire)

Misfire History #1-#4

Misfire

0-255 Counts

0 (increase with a misfire)

Med. Resolution Resync Counter

Engine 1

0-255 Counts

0

Med. Resolution Engine Sync.

Engine 1

Yes/No

Yes

Number of DTCs

Engine 1

EVAP

Misfire

O2S

Number

0

Number of catalyst Mon. Test Completed

O2S

Number of samples

Varies

O2S 1

Engine 1

EVAP

O2S

mV

1-1000 and varying

Power Enrichment

Engine 1

Active/Inactive

Inactive

Purge Learned Memory

EVAP

Counts

1.00

Rich/Lean Transition

O2S

0-255 Counts

0

Rich/Lean Average Time

O2S

mS

0

Short Term FT

Engine 1

EVAP

O2S

%

0% +/- 10%

Spark

Engine 1

Degrees

Varies

TCC Brake Switch

Engine 2

Open/Closed

Closed

Total Misfire Current Counter

Misfire

0-255 Counts

0 (increase with a misfire)

TP Angle

Engine 1

Engine 2

EVAP

Misfire

O2S

%

0% (up to 100% at wide open throttle)

TP Sensor

Engine 1

Engine 2

EVAP

Misfire

O2S

Volts

0.200--0.900 volts (up to 5.0 volts at wide open throttle)

Transmission Range

Engine 2

Invalid/Low/Drive 2/Drive 3/Overdrive/Reverse/Park/Neutral

Park/Neutral (Auto trans only)

TR Switch P A B C

Engine 2

Low/High

Low/Low/High/High

TWC Stage 1 Started

O2S

Yes/No

Yes

TWC Stage 2 Started

O2S

Yes/No

Yes

TWC System Related DTC is Set

O2S

Yes/No

No

TWC Test Initialization Conditions Met

O2S

Yes/No

Yes

TWC Test Enabled

O2S

Yes/No

No

TWC Warmup Conditions Met

O2S

Yes/No

Yes

Vacuum Calculated

Engine 2

kPa/PSI

Varies with the engine Load

Vehicle Speed

Engine 1

Engine 2

Km/h/MPH

0