GM Service Manual Online
For 1990-2009 cars only
A/C Relay Command: Displays YES if the PCM is commanding the A/C relay On.

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

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

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

Air Pump Relay Command: Displays ON if the PCM is commanding the air pump relay On.

Air Pump Solenoid CMD: Display On if the PCM is commanding the air pump solenoid On.

BARO: Barometric pressure is determined by reading the MAP sensor value with the ignition On, engine Off or during a wide open throttle condition.

Brake Switch: Displays APPLIED when the brake pedal is being depressed (switch open).

Calc. Converter Temp: Indicates PCM calculated catalytic converter temperature at idle. Calculation is based on ECT, engine run time, engine speed and power enrichment/decel conditions.

CMP Resync Counter: Every crankshaft revolution, there are 7 pulses generated by the CKP sensor from the notches on the crankshaft. Each pulse represents one count. The counter can count as high as 255. Under most engine operating conditions, the PCM receives a #4 cylinder TDC compression signal from the EI module. The PCM will reset the counter to 0 when this signal is received. NOTE: The EI module cannot determine #4 cylinder TDC compression during deceleration and therefore the PCM will not reset the counter to zero during this condition.

Cooling Fan Relay CMD: Displays ON if the PCM is commanding the cooling fan relay On.

Crank Learned: Displays YES if the PCM has learned the variation between crankshaft reluctor notch spacing. Learning the crankshaft is vital to correct misfire diagnostics.

Cruise Clutch Command: Displays YES if the PCM is commanding the cruise control module clutch On.

Cruise Delta: Displays the difference between the cruise set speed and the actual vehicle speed.

Cruise Direction Command: Displays YES if the PCM is commanding cruise direction.

Cruise In Released State: Displays YES if the PCM has disengaged cruise.

Cruise Resume/Accel: Displays ON if the RES/ACCEL switch is depressed.

Cruise Set Speed: Indicates the set vehicle cruise speed.

Cruise Set/Coast: Displays ON if the SET/COAST switch is depressed.

Cruise Switch: Displays ON if the CRUISE ON/OFF switch is On.

Cruise Switch Voltage: Indicates the value of the cruise control signal voltage at the PCM.

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.

Dist. Since Code Clear: Indicates the number of miles the vehicle has traveled since the last time the PCM DTCs were cleared.

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

EGR CV Fail Pending: Displays YES when the PCM fails an initial EGR closed valve test. The PCM will take more tests to determine if the valve is truly stuck open before DTC P1404 (EGR not Indicating Closed) sets.

EGR Decel Test Filter: Indicates the number of MAP sensor counts that changed as a result of an EGR test that opens the EGR valve during deceleration. The filter counts must be higher than the EGR DECEL THRESHOLD during the same test in order to pass.

EGR Decel Threshold: Indicates the minimum number of MAP sensor counts that must change as a result of an EGR test that opens the EGR valve during deceleration.

EGR Duty Cycle: Indicates the percentage of EGR solenoid On-time the PCM is commanding. NOTE: The percent duty cycle will NOT equal percent open.

EGR Flow Test Count: Indicates the number of EGR deceleration flow tests that have been performed since PCM DTCs have been cleared. The test runs once per ignition cycle once the correct conditions have been met. The counter range is 0-255.

EGR Position - Actual: Indicates the percentage of EGR valve opening based on the EGR sensor signal voltage at the PCM. Percentage is a conversion from voltage.

EGR Position - Command: Indicates the percentage of EGR valve opening as commanded by the PCM.

EGR Position - Delta: Indicates the percent difference between the actual and commanded EGR position.

EGR Sensor: Indicates the value of the EGR sensor signal voltage at the PCM.

EGR Sensor - Closed: When EGR is commanded Off, the PCM learns the closed EGR sensor signal voltage. This parameter is the learned value.

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

Engine Oil Life Remaining: Percentage of engine oil life left based on engine revolutions, ECT and vehicle mileage. At 10% engine oil life left, the PCM will send a message to the I/P cluster over the Class II link to turn On the CHANGE OIL SOON telltale.

Engine Oil Life Reset: Displays YES when the oil life reset switch in the UHFB is being depressed (switch closed).

Engine Run Time: Indicates the amount of time the engine has been running since the ignition was turned On.

Engine Speed: Indicates the crankshaft speed in revolutions per minute as indicated by the PCM based on the CKP sensor signal. The CKP sensor creates voltage pulses from the 7 notches on the crankshaft.

EVAP Large Leak: Indicates the PASS or FAIL result of the EVAP large leak diagnostic during the EVAP diagnostic system test. NOT RAN means the test has not run this ignition and INV means the test results were invalid. A FAIL indicates a large leak is present.

EVAP Purge Valve Leak: Indicates the PASS or FAIL result of the EVAP purge solenoid diagnostic test during the EVAP diagnostic system test. NOT RAN means the test has not run this ignition and INV means the test results were invalid. A FAIL most likely indicates the EVAP purge solenoid is stuck open.

EVAP Small Leak: Indicates the PASS or FAIL result of the EVAP small leak diagnostic during the EVAP diagnostic system test. NOT RAN means the test has not run this ignition and INV means the test results were invalid. A FAIL indicates a small leak is present.

EVAP Vent Blockage: Indicates the PASS or FAIL result of the EVAP vent solenoid diagnostic test during the EVAP diagnostic system test. NOT RAN means the test has not run this ignition and INV means the test results were invalid. A FAIL most likely indicates the EVAP vent solenoid is stuck closed or an EVAP line from the vent to the fuel tank is kinked.

EVAP Purge Solenoid: Displays ON if the PCM is commanding a duty cycle to the EVAP purge solenoid.

EVAP Purge Solenoid DC: Indicates the EVAP purge solenoid On-time percentage the PCM is commanding.

EVAP Tank Vac. Filtered: The rate at which the vacuum in the fuel tank is changing. Value is based off the fuel tank pressure sensor.

EVAP Tank Vac. Slope: Indicates the rate at which the vacuum in the fuel tank during the EVAP system small and large leak diagnostic test is decreasing (losing vacuum). Units are in millimeters of mercury per second.

EVAP Vent Solenoid: Displays ON if the PCM is commanding the EVAP vent solenoid On.

Fuel Cutoff: Displays ON if the PCM is commanding the fuel injectors Off due to high RPM.

Fuel Level: Indicates the fuel level in the fuel tank based on the fuel level sensor signal voltage at the PCM. Fuel level is a conversion from voltage.

Fuel Level Sensor: Indicates the value of the fuel level sensor voltage at the PCM based on fuel tank level.

Fuel Pump Relay Command: Displays ON if the PCM is commanding the fuel pump relay On.

Fuel Tank Pressure: Indicates the vapor pressure above the fuel in the fuel tank based on the fuel tank pressure sensor signal voltage at the PCM. Normal readings with the fuel cap Off should be within 1.3-1.7 volts or at atmospheric pressure, 101 kPa. Pressure is a conversion from voltage.

Fuel Tank Pressure 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.

Fuel Trim Cell #: Indicates the long term fuel trim cell the PCM is currently using for fuel control when the system is in closed loop. 0=decel, 1=idle, 2=cruise, 3=accel.

High Spark Modifier: LOW, MID and HIGH SPARK MODIFIERS are adaptive spark retard values used to control engine spark knock. The HIGH SPARK MODIFIER should display 0 degrees if no spark retard is needed. The high spark modifier is used for high 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.

HO2S 2: Indicates the voltage across the heated oxygen sensor 2 detected at the PCM HO2S-2 inputs. A bias voltage of 391-491 mV from the PCM should be read on Scan tool when the sensor is cold. Normal operating ranges will remain fairly steady around 500-800 mV.

IAC Position: Indicates the current idle air control valve position calculated by the PCM.

IAC Position W/O A/C: Indicates the learned idle air control position with the A/C Off.

IAC Position With A/C: Indicates the learned idle air control position with the A/C On.

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

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

Injector Pulse Width: Indicates the base fuel injector On-time the PCM is commanding.

Knock Retard Cyl. # (1, 2, 3, 4): Indicates the amount of spark retard the PCM is commanding from the normal calculated spark advance.

KS Noise: Indicates the level of normal noise as seen by the knock sensor at idle. The higher the count value, the higher the amplitude of the noise. Normal noise levels will vary with the SOHC and DOHC engines.

Lean/Rich Avg. Time: Indicates the average time for the O2S-1 to transition from under 300 mV to over 600 mV during the last test sample.

Lean/Rich Transitions: Indicates the number of times the O2S-1 transitioned from under 300 mV to over 600 mV during the last test sample.

Long Term Fuel Trim: Indicates an averaged fuel correction factor from the short term fuel trim values based on the O2S-1 signal. Nominal values should be near 0 percent correction. A positive percentage indicates the PCM is adding fuel to maintain a 14.7:1 air/fuel ratio. A negative percentage indicates the PCM is decreasing fuel to maintain a 14.7:1 air/fuel ratio.

Loop Status: Displays the fuel control status the PCM is using. Closed indicates the PCM is using the O2S-1 signal to make fuel corrections. The O2S-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 O2S-1 to control fuel, but using stored values based on ECT, IAT, MAP and TP sensor information.

Low Coolant Level: Displays YES if the coolant in the coolant surge tank is low (switch open).

Low Spark Modifier: LOW, MID and HIGH SPARK MODIFIERS are adaptive spark retard values used to control engine spark knock. The LOW SPARK MODIFIER should display 0 degrees if no spark retard is needed. 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 always works back to zero compensation or no spark retard.

M/T Clutch Disengaged: Displays YES if the PCM has detected engine flare as a result of the clutch pedal being depressed. There is NO clutch pedal input to the PCM.

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.

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

Mid Spark Modifier: LOW, MID and HIGH SPARK modifiers are adaptive spark retard values used to control engine spark knock. The MID SPARK MODIFIER should display 0 degrees if no spark retard is needed. The mid spark modifier is used for mid 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 always works back to zero compensation or no spark retard.

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 finished. The counters will then be updated to the history misfire counters as the current counters are reset to zero.

Misfire Enabled: Displays YES when the PCM has detected that all of the misfire enable criteria have been met. Parameters can be found under P0300 DTC PARAMETERS.

Misfire History Cyl. # (1, 2, 3, 4): 200 revolution misfire tests which update current misfire counter information. The current counters will be reset to zero once the 200 revolutions are finished. The counters will then be updated to the history misfire counters. The history misfire counters will be reset to 0 every ignition cycle unless DTC P0300 is active. The history counter can only be cleared using scan tool.

O2S 1: Indicates the output voltage of the oxygen sensor 1 as detected at the PCM O2S-1 signal input. A bias voltage of 391-491 mV from the PCM should be read on Scan tool when sensor is cold. Normal operating ranges will range from 10-999 mV.

O2S Transition Time Ratio: After the 100 second O2S-1 test has been performed, this parameter will indicate the ratio of the rich/lean to lean/rich average transition times.

Park/Neutral Switch: Displays P-N or R-D-L as indicated from the transaxle range switch.

Rich/Lean Avg. Time: Indicates the average time for the O2S-1 to transition from over 600 mV to under 300 mV during the last test sample.

Rich/Lean Transitions: Indicates the number of times for the O2S-1 to transition from over 600 mV to under 300 mV during the last test sample.

Short Term Fuel Trim: Indicates the fuel correction factor value based on the O2S-1 signal. Nominal values should be near 0 percent correction. A positive percentage indicates the PCM is adding fuel to maintain a 14.7:1 air/fuel ratio. A negative percentage indicates the PCM is decreasing fuel to maintain a 14.7:1 air/fuel ratio.

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

Startup ECT: Indicates the temperature of the engine coolant based on the ECT sensor signal voltage at the PCM when the ignition is first turned On. The value is stored until the ignition is cycled. Temperature is a conversion from voltage.

Steering Assist Sol. DC: Indicates the steering assist solenoid On-time percentage the PCM is commanding. Under 16 km/h (10 mph), the duty cycle will be 0% or full assist. Over 113 km/h (70 mph) the duty cycle will be 100% or no assist. In between speeds will vary.

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

TP Sensor: Indicates the TP sensor signal voltage at the PCM.

Vehicle Speed: Indicates vehicle speed as indicated by the PCM based on the output speed sensor (OSS) signal. The OSS creates voltage pulses from notches off the differential housing carrier in the transaxle.