GM Service Manual Online
For 1990-2009 cars only

PARAMETER

DEFINITION

TABLE

A/C High Side Press. Sensor

Indicates the A/C pressure sensor signal voltage at the PCM based on air conditioning high side pressure.

0, 1

A/C High Side Pressure

Indicates air conditioning high side pressure based on the A/C pressure sensor signal voltage at the PCM. This parameter is used to control A/C relay and cooling fan(s) operation. Pressure is a conversion from voltage.

0

A/C Relay CKT Open Short to GND

Displays YES if the A/C relay control circuit feedback voltage at the PCM is too low when the A/C relay is commanded Off.

1

A/C Relay Ckt Short To Volts

Displays YES if the A/C relay control circuit feedback voltage at the PCM is too high when the A/C relay is commanded On.

1

A/C Relay Command

Displays YES if the PCM is commanding the A/C relay On.

0, 1, 6

A/C Request

Displays YES if the PCM received an A/C request from the BCM. The BCM receives the input form the HVAC control head via the A/C On/Off switch or defrost selection.

0, 1, 6

Air Flow

Mass of air per unit time entering the engine calculated by the PCM based on MAP and engine speed.

7

Air Fuel Ratio

Indicates the number of parts of air to one part of fuel the PCM is currently commanding and driving towards.

2

Air Pump Relay Command

Displays YES if the PCM is commanding the air pump relay On.

1, 5

Air Relay CKT Open Short to GND

Displays YES if the air pump relay control circuit feedback voltage at the PCM is too low when the air pump relay is commanded Off.

1

Air Pump CKT Short to Volts

Displays YES if the air pump relay control circuit feedback voltage at the PCM is too high when the air pump relay is commanded On.

1

BARO

Barometric pressure (outside air pressure) is determined by reading the MAP sensor value with the ignition On, engine Off or during a wide-open-throttle condition.

2

Cal. Compression Output

Indicates a binary number which represents the cam output from the EI module to the PCM. Normal readings during all engine running conditions except decel, should read 00000110 or 00001001. This depends on where the camshaft is.

4

Calc. Converter Temp

Indicates PCM calculated catalytic converter temperature. Calculation is based on ECT, engine run time, engine speed and power enrichment/decel conditions.

7

CKP Active Counter

Indicates the number of 7X pulses the PCM has received from the EI module. The EI module produces the 7X pulses based on the AC voltage from the CKP sensor. One count equals one notch passed on the crankshaft.

0, 3

CMP Active Counter

Indicates the number of compression sense (cam) pulses the PCM has received from the EI module.

0, 3

CMP Resync Counter

Indicates the number of times the PCM has to resync the compression sense (cam) input. This number will only increment if 7X pulses are intermittently lost; therefore, the counter should always remain at zero if the engine is running normally.

0, 3

Cruise Brake/Clutch SW

Displays APPLIED when the brake or clutch pedal is being depressed (switch closed-brake switch, switch open-clutch switch). Input is used for TCC and cruise control engage/disengage.

0, 6

Cruise Enabled

Displays YES if the PCM is allowing cruise control to be enabled. The PCM will ground the cruise enable circuit to the cruise control module to enable cruise control when certain conditions have been met.

0, 6

Cruise Engaged

Displays YES if the cruise control module is controlling cruise operation. The cruise control module will supply a ground to the cruise engage circuit when the cruise control module is in control of vehicle speed.

0, 6

Desired Idle Speed

Indicates the idle engine speed the PCM is commanding. Desired idle speed is based on ECT, transaxle range switch position and A/C On/Off.

6

ECT

Indicates the temperature of the engine coolant based on the ECT sensor signal voltage at the PCM. Temperature is a conversion from voltage.

0, 1, 2, 3, 4, 5, 6, 7

Engine Load

Engine load value is calculated by the PCM based on engine speed, MAP and TP sensor values.

0, 1, 2, 3, 4, 5, 6, 7

Engine Oil Life Remaining

Percentage of engine oil life left based on engine revolutions, ECT and vehicle mileage. At 5% engine oil life left, the PCM will send a message to the BCM which will send a message to the I/P cluster over the Class II link to turn On the CHANGE OIL SOON telltale.

0

Engine Run Time

Indicates the amount of time the engine has been running since the ignition was turned On.

0

Engine Speed

Indicates the crankshaft speed in revolutions per minute as indicated by the PCM based on the 7X reference signal received from the EI module. The EI module receives the crankshaft speed from the CKP sensor AC signal voltage.

0, 1, 2, 3, 4, 5, 6, 7

EVAP Large Leak

Indicates the PASS, FAIL, ABORTED or NOT RAN result of the EVAP large leak diagnostic during the EVAP diagnostic system test. NOT RAN means the test has not run this ignition cycle. ABORTED means that the test began to run and was terminated due to criteria changes. A FAIL indicates a large leak is present.

5

EVAP Purge CKT Open Short to GND

Displays YES if the EVAP purge solenoid control circuit feedback voltage at the PCM is too low when the EVAP purge solenoid is commanded Off.

1

EVAP Purge CKT Short to Volts

Displays YES if the EVAP purge solenoid control circuit feedback voltage at the PCM is too high when the EVAP purge solenoid is commanded On.

1

EVAP Purge Solenoid DC

Indicates the EVAP purge solenoid On-time the PCM is commanding.

1, 2, 5

EVAP Vent CKT Open Short to GND

Displays YES if the EVAP vent solenoid control circuit feedback voltage at the PCM is too low when the EVAP vent solenoid is commanded Off.

1

EVAP Vent CKT Short to Volts

Displays YES if the EVAP vent solenoid control circuit feedback voltage at the PCM is too high when the EVAP vent solenoid is commanded On.

1

EVAP Vent Solenoid

Displays YES if the PCM is commanding the EVAP vent solenoid On (closed valve, no venting).

1

Fan Control 1 Command

Displays YES if the PCM is grounding the fan control 1 circuit. This logic output is used by the PCM in conjunction with FAN CONTROL 2 to command the cooling fan control module to run the cooling fans at a given speed.

1

Fan Control 2 Command

Displays YES if the PCM is gounding the fan control 2 circuit. This logic output is used by the PCM in conjunction with FAN CONTROL 1 to command the cooling fan control module to run the cooling fans at a given speed.

1

FC 1 Relay CKT Open/Short To GND

Displays YES if the fan control 1 control circuit feedback voltage at the PCM is too low when fan control 1 is commanded Off.

1

FC 1 Relay CKT Short To Volts

Displays YES if the fan control 1 control circuit feedback voltage at the PCM is too high when fan control 1 is commanded On.

1

FC 2 Relay CKT Open/Short to GND

Displays YES if the fan control 2 control circuit feedback voltage at the PCM is too low when fan control 2 is commanded Off.

1

FC 2 Relay CKT Short To Volts

Displays YES if the fan control 2 control circuit feedback voltage at the PCM is too high when fan control 2 is commanded On.

1

Fuel Cutoff

Displays On if the PCM is commanding the fuel injectors Off due to high engine or vehicle speed.

2

Fuel Level

Indicates the level of fuel in the fuel tank based on the fuel level sensor signal voltage at the PCM. The percentage on Scan tool, which is a conversion from voltage, is averaged over time for the EVAP diagnostics.

0, 2, 3

Fuel Pump Relay Command

Displays ON if the PCM is commanding the fuel pump relay On.

1

Fuel Tank Press. Sensor

Indicates the fuel tank pressure sensor signal voltage at the PCM based on the difference between the outside air pressure and internal fuel tank vapor pressure.

0, 5

Fuel Trim Cell #

Indicates the current long term fuel trim cell the PCM is using for fuel control when the system is in closed loop. Twenty-two cells are used based on RPM and MAP sensor values.

2

Generator F Terminal DC

Input from the generator to the PCM indicating generator electrical load. If electrical load increases at idle, the PCM will adjust idle speed accordingly.

1

Generator L Terminal

Displays ENABLED if the PCM is supplying the generator 5 volts necessary for charging. The PCM can disable the generator to ease starting during engine crank if battery voltage is too low.

1

HO2S Transition Time Ratio

After a 100 second HO2S-1 test has been performed, this parameter will indicate the ratio of the rich/lean to lean/rich average transition times.

7

HO2S 1

Indicates the output voltage of the oxygen sensor 1 as detected at the PCM HO2S-1 inputs. A bias voltage of 399-499 mV from the PCM should be read when the sensor is cold. Normal operating ranges will range from 10 mV to 1065 mV.

0, 2, 5

HO2S 2

Indicates the voltage across the heated oxygen sensor 2 detected at the PCM HO2S-2 inputs. A bias voltage of 425-460 from the PCM should be read when the sensor is cold. Normal operating ranges will remain fairly steady around 500-800 mV when the vehicle is at normal operating temperature.

0, 3, 5

HO2S 1 Heater Command

Indicates the output voltage of the oxygen sensor 1 as detected at the PCM HO2S-1 inputs. A bias voltage of 399-499 mV from the PCM should be read when the sensor is cold. Normal operating ranges will range from 10 mV to 1065 mV.

5

HO2S 2 Heater Command

Indicates the voltage across the heated oxygen sensor 2 detected at the PCM HO2S-2 inputs. A bias voltage of 425-460 from the PCM should be read when the sensor is cold. Normal operating ranges will remain fairly steady around 500-800 mV when the vehicle is at normal operating temperature.

5

IAC position

Indicates the current idle air control position in counts the PCM is commanding.

6

IAT

Indicates the temperature of the air entering the engine based on the IAT sensor signal voltage at the PCM. Temperature is a conversion from voltage.

0, 1, 2, 3, 4, 5, 6, 7

Ignition 1

Indicates ignition voltage at the ignition 1 voltage supply to the PCM. This voltage is referenced to PCM ground, which is tied to chassis ground.

0, 1, 2, 3, 4, 5, 6, 7

Injector Pulse Width

Indicates fuel injector #2 On-time the PCM is commanding.

2

Knock Retard

Indicates the amount of spark retard the PCM is commanding from the normal calculated spark advance. This is in response from the knock sensor AC signal voltage detected.

3

KS Active Counter

Indicates knock sensor counts based on the knock sensor AC signal voltage at the PCM.

3

KS Noise

Indicates an amplified knock sensor AC signal voltage at the PCM. The Scan tool will indicate close to a 10 times amplification rate then what the sensor is actually outputting.

3

Lean/Rich Avg Time

Indicates the average time for the HO2S-1 to transition from under 300 mV to over 600 mV during the last test sample.

7

Lean/Rich Transitions

Indicates the number of times the HO2S-1 transitioned from under 300 mV to over 600 mV during the last test sample.

7

Long Term FT

Indicates an averaged fuel correction factor from the short term fuel trim values based on the HO2S-1 signal. Nominal values should be near 0% correction. A positive percentage indicates the PCM is adding fuel to maintain a 14.7 to 1 air/fuel ratio. A negative percentage indicates the PCM is decreasing fuel to maintain a 14.7 to 1 air/fuel ratio.

2, 3, 5

Loop Status

Displays the fuel control status the PCM is using. Closed loop indicates the PCM is using the HO2S-1 signal to make fuel corrections. The HO2S-1 signal must go above 600 mV or below 300 mV before the PCM will go into closed loop. Open loop indicates the PCM is not using the HO2S-1 to control fuel, but using stored values based on ECT, IAT, MAP and TP sensor information.

2

Low Oil Pressure

Displays YES if the engine oil pressure is low (switch closed, circuit grounded).

0

Low Spark Modifier

Indicates adaptive spark retard values use to control engine spark knock. The low spark modifier is used for low engine speeds. The adaptives are based on ECT and will reset to 0 degrees during cold temperatures. If a hot restart occurs, a percentage of the learned adaptive will be used. The PCM will always work back to zero compensation or no spark retard.

3

MAP

Indicates manifold absolute pressure based on the MAP sensor signal voltage at the PCM. This parameter is used to calculate engine load and barometric pressure. Pressure is a conversion from voltage.

0, 1, 2, 3, 4, 5, 6, 7

MAP Sensor

Indicates the manifold absolute pressure sensor signal voltage at the PCM based on the intake manifold absolute pressure.

0

Misfire Current Cyl # (1, 2, 3, 4)

Indicates current cylinder misfires. The PCM runs 200 revolution misfire tests which update current misfire counter information. The current counters will be reset to zero once the 200 revolutions are completed. The current counters will only update to the history counters once a misfire DTC has been set.

4

Misfire History Cyl. # (1, 2, 3, 4)

Indicates history cylinder misfires. The PCM runs 200 revolution misfire tests which update current misfire counter information. The current counters will be reset to zero once the 200 revolutions are completed. The current counters will only update to the history counters once a misfire DTC has been set. The history counts will only store counts through ignition cycles if the MIL is commanded On.

4

Module Driver Overtemp

Displays YES if the PCM is turning its output driver module Off due to an overheated condition.

1

Module Drive Overvoltage

Displays YES if the PCM is turning its output driver module Off due to an overvoltage condition.

1

Park/Neutral Switch

Displays P-N or RDL as indicated from the transaxle range switch.

6

Rich/Lean Avg. Time

Indicates the average time for the HO2S-1 to transition from over 600 mV to under 300 mV during the last test sample.

7

Rich/Lean Transitions

Indicates the number of times the HO2S-1 transitioned from over 600 mV to under 300 mV during the last test sample.

7

Short Term FT

Indicates the current fuel correction factor based on the HO2S-1 signal. Nominal values should be near 0 percent correction. A positive percentage indicates the PCM is adding fuel to maintain a 14.7 to 1 air/fuel ratio. A negative percentage indicates the PCM is decreasing fuel to maintain a 14.7 to 1 air/fuel ratio.

2, 3, 5

Spark

Indicates the number of commanded degrees of spark advance. A positive number means before TDC and a negative number means after TDC.

3

Startup ECT

Indicates the temperature of the engine coolant based on the ECT sensor signal voltage at the PCM when the engine is first started. Temperature is a conversion from voltage.

2

Torque Requested

Indicates an engine torque reduction level signal from the EBTCM that the PCM uses to reduce engine power. This power reduction is used to control wheel slip for traction control acceleration.

0

TP Angle

Indicates throttle plate angle based on the TP sensor signal voltage at the PCM. Throttle plate angle is a conversion from voltage.

0, 1, 2, 3, 4, 5, 6, 7

TP Sensor

Indicates the TP sensor signal voltage at the PCM.

0

Vehicle Speed

Automatic Transaxle: The PCM receives vehicle speed from the output shaft speed sensor signal AC voltage.

Manual Transaxle with ABS: The PCM receives vehicle speed from the EBTCM. The EBTCM receives this vehicle speed from the right front wheel speed sensor AC signal voltage.

Manual Transaxle without ABS: The PCM receives vehicle speed from the wheel speed signal conditioner module. The conditioner module receives this vehicle speed from the right front wheel speed sensor. The conditioner module converts the AC voltage from the sensor to a pulse width modulated ground which the PCM interprets as a square wave.

0, 1, 2, 3, 4, 5, 6, 7