Engine Scan Tool Data Definitions. Buick Roadmaster 1996

For 1990-2009 cars

The Engine Scan Tool Data Definitions contains a brief description of all engine related parameters that are available on the scan tool. The list is arranged in alphabetical order. A given parameter may appear in any one of the data lists, and in some cases may appear more than once, or in more than one data list in order to group certain related parameters together.

1-4 Shift Sol.: Scan Tool Displays Enabled or Disabled (Y Car Only). When the PCM enables the 1-4 shift solenoid, the scan tool will display Enabled.
A/C Clutch: Scan Tool Displays On or Off. Represents the commanded state of the A/C clutch control relay. The A/C clutch should be engaged when ON is indicated on the scan tool.
A/C Evap. Temp.: Scan Tool Range -18°C to 53°C (0°F to 128°F) (F Car Only). The scan tool will display the A/C evaporator temperature. This sensor is used by the PCM to cycle the A/C compressor clutch. This sensor is also used to prevent A/C evaporator freeze-up.
A/C High Side: Scan Tool Displays 15-452psi/0.00-5.00 Volts. Represents the A/C refrigerant pressure sensor signal. The amount of pressure indicates the amount of load that the A/C compressor is placing on the engine. The PCM uses this information to adjust idle and to control the cooling fans.
A/C Request: Scan Tool Displays Yes or No. Indicates the state of the A/C request input circuit from the HVAC controls. The PCM uses the A/C request signal to determine whether A/C compressor operation is being requested.
A/C Status: Scan Tool Displays On or Off. The scan tool will display ON when voltage is applied to the A/C compressor clutch.
A/T Perf. Mode: Scan Tool Displays Normal or Perf (F Car Only). This parameter is the actual state of the performance mode control program within the PCM. The scan tool will display Perf. when the performance mode is enabled (Performance Shift Calibration). The scan tool will display Normal when the performance mode is disabled (Normal Shift Calibration).
A/T Perf. Switch: Scan Tool Displays Inactive or Active (F Car Only). This parameter indicates the position of the performance mode switch. The scan tool will display Active when the switch is depressed and then Inactive when the switch is released.
AIR Pump: Scan Tool Displays Disabled or Enabled. When the PCM enables the Secondary Air Injection (AIR) pump the scan tool will indicate ENABLED. When the PCM turns the AIR pump off, the scan tool will indicate DISABLED.
ASR/TCS Spark Retard: Scan Tool Displays No or Yes (If so equipped). When the traction control system requires reduced engine torque, the PCM will retard the engines' timing. When this occurs, the scan tool will display Yes.
BARO: Scan Tool Range 10-105 kPa/0.00-5.00 Volts. The Barometric Pressure reading is determined from the MAP sensor signal monitored during key up and Wide-Open Throttle (WOT) conditions. The Barometric Pressure is used to compensate for altitude differences.
CKP Engine Speed: Scan Tool Range 0-9999 RPM. The crankshaft engine speed is computed by the PCM from the crankshaft position sensor signal. The CKP engine speed should remain close to actual engine speed.
CKP:Lo Res Angle: Scan Tool Range +60 to -30°Dev. This parameter is the actual timing relationship between the crankshaft and the camshaft in degrees. Ideally the value would be zero indicating that the cam is neither advanced or retarded relative to the crank. Under normal operation, this value can be expected to fluctuate slightly above or below zero. As timing chain wear increases, the deviation will increase.
Cold Start Up: Scan Tool Displays Yes or No. When the engine coolant temperature and intake air temperatures are less than 50°C (122°F) and are within 3°C (5°F) of each other at start-up, is consider a cold start-up. When these temperatures are in the range, the scan tool will indicate YES. When the scan tool displays YES, indicates a cold start-up was detected.
Current Gear: Scan Tool Displays 1, 2, 3, or 4. The PCM looks at Trans Range position and the gear commanded by the PCM. The actual forward gear that the transmission is in will be the lower of the two because the manual valve can override the PCM commanded gear.
Cycles of Misfire Data: Scan Tool Range 0-100. Counts the number of Misfire tests during 200 revolutions.
Cyl. Mode Misfire Index: Scan Tool Range 0-65535. This parameter displays the amount of crankshaft decelerations. When an engine is operating without a misfire, the scan tool will display less then 1000 counts. When an engine misfire occurs, the counter will be greater then 1000 counts.
Desired Idle: Scan Tool Range 0-3187 RPM. The idle speed that is commanded by the PCM. The PCM will compensate for various engine loads based on engine coolant temperature to keep the engine at the desired speed.
DTC: Scan Tool Range P0001-P1999. This parameter indicates what DTC is stored within freeze frame and/or Failure Records buffer.
DTC Set This Ign.: Scan Tool Displays Yes or No. This parameter indicates if a Diagnostic Trouble Code has set on the current ignition cycle.
ECT: Scan Tool Range -40°C to 151°C (-40°F to 304°F). The Engine Coolant Temperature (ECT) sensor is mounted in the coolant pump. The PCM applies 5 volts to the ECT sensor circuit. The sensor is a thermistor which changes internal resistance as temperature changes. When the sensor is cold (internal resistance high), the PCM monitors a high signal voltage and interprets it as a cold engine. As the sensor warms (internal resistance decreases), the voltage signal will decrease and the PCM will interpret the lower voltage as a warm engine.
EGR Duty Cycle: Scan Tool Range 0%-100% (L99 and LT1 Only). The PCM turns the EGR on and off. The ON time of the EGR solenoid valve is the duty cycle. This ON time is expressed as a percent. The amount of the percent is the amount of time the EGR valve is open.
Engine Load: Scan Tool Range 0%-100%. Engine load is calculated by the PCM from engine speed and MAF sensor readings. Engine Load should increase with an increase in RPM or airflow.
Engine Oil Temp.: Scan Tool Range -40°C to 164°C (-40°F to 327°F) (Y Car Only). The scan tool will display the Engine Oil Temperature. The engine oil temperature is used by the PCM to control the cooling fans.
Engine Run Time: Scan Tool Displays Seconds, Minutes, Hours. This indicates the amount of time the engine has been operating. When the ignition is cycled off the timer will be set to zero.
Engine Speed: Scan Tool Range 0-20000 RPM. Engine speed is computed by the PCM from the low resolution signal. It should remain close to desired idle under various engine loads with engine idling.
EVAP Purge: Scan Tool Range 0%-100%. Represents the PCM commanded PWM duty cycle of the EVAP Purge Solenoid valve. 0% displayed indicates no purge; 100% displayed indicates full purge.
EVAP Vacuum SW.: Scan Tool Displays Purge or No Purge. The EVAP purge vacuum switch is a normally closed switch positioned in the purge line between the canister and the EVAP purge solenoid. The EVAP purge vacuum switch will open when vacuum increases to greater than 5 inches of water in the purge line. The EVAP Purge Vacuum Switch is used by the PCM to monitor EVAP canister purge solenoid operation and purge system integrity. The EVAP Purge Vacuum Switch should be closed to ground with no vacuum present (0% EVAP Purge PWM). With EVAP Purge PWM at 25% or greater, the EVAP Purge Vacuum Switch should open and purge should be indicated.
Fail Counter: Scan Tool Range 0-255. When a MIL is requested or a history DTC is stored, the PCM will count and store the amount times a diagnostic test failed. This information will be stored in Freeze Frame or Failure records. Only one DTC can be stored in each Freeze Frame and/or Failure Records buffers.
FC Relay 1: Scan Tool Displays On or Off. When the PCM commands a coolant fan ON, the scan tool will indicate ON. Some vehicles are equipped with a three relay configuration. When the PCM commands the fan one relay control ON, both fans will be enabled on low speed.
FC Relay 2: Scan Tool Displays On or Off (B and D Car without Heavy Duty Cooling). When the PCM commands a coolant fan ON, the scan tool will indicate ON.
FC Relay 2 and 3: Scan Tool Displays On or Off (F and Y Car Only). When the PCM commands a coolant fan ON, the scan tool will indicate ON.
Fuel Trim Cell: Scan Tool Range 0-255. This parameter indicates what Fuel trim cell is currently active.
Fuel Trim Learn: Scan Tool Displays No or Yes. When conditions are appropriate for enabling long term fuel trim corrections, Fuel Trim Learn will display YES. This indicates that the long term fuel trim is responding to the short term fuel trim. If the Fuel Trim Learn displays NO, then long term fuel trim will not respond to changes in short term fuel trim.
High Res. Signal: Scan Tool Displays Inactive or Active. This signal is generated by the ignition control module. When the PCM detects a high resolution signal, the scan tool display will change from inactive to active.
HO2S Bn1 and Bn2 Sen. 1: Scan Tool Range 0-1107 mV. Represents the fuel control exhaust oxygen sensor output voltage. Should fluctuate constantly within a range between 10 mV (lean exhaust) and 1000 mV (rich exhaust) while operating in 'Closed Loop.'
HO2S Bn1 and Bn2 Sen. 2: Scan Tool Range 0-1107 mV. Represents the fuel control exhaust oxygen sensor output voltage. Should fluctuate constantly within a range between 10 mV (lean exhaust) and 1000 mV (rich exhaust) while operating in 'Closed Loop.'
IAC Learned: Scan Tool Range 0-255. IAC learned is an internal PCM parameter. Each time the vehicle is driven the IAC system learns how many counts is required to produce a given desired idle.
IAC Position: Scan Tool Range 0-255 . Displays the commanded position of the idle air control pintle in counts. A larger number of counts means that more air is being commanded through the idle air passage. Idle air control should respond fairly quickly to changes in engine load to maintain desired idle RPM.
IAT: Scan Tool Range -40°C to 151°C (-40°F to 304°F). The PCM converts the resistance of the intake air temperature sensor to degrees. Intake Air Temperature (IAT) is used by the PCM to adjust fuel delivery and spark timing according to incoming air density.
Ignition Volts: Scan Tool Range 0.0-25.5 volts. This parameter is the battery ignition voltage input to the PCM.
Inj. Avg. PWM Bn1 and Bn2: Scan Tool Range 0-1000 m/sec. Indicates the amount of time the PCM is commanding each injector ON during each engine cycle. A longer injector pulse width will cause more fuel to be delivered. Injector Pulse Width should increase with increased engine load.
Knock Retard: Scan Tool Range 0.0°-16°. Indicates the amount of spark the PCM is removing from IC spark advance in response to the signal from the Knock sensors.
KS Activity: Scan Tool Displays Yes or No. Indicates whether or not a KS activity is being detected by the PCM. With the engine idling, the scan tool should indicate NO.
LT FT Avg. Bn1 and Bn2: Scan Tool Displays Counts/Percentage. This parameter indicates the average of all long term fuel trim cells. The short term fuel trim cells are rated (Weighted) for the amount of which they are used. For example, an idle cell will be rated higher then a wide open cell. If a fueling malfunction is occurring in the idle cell and the wide open cell, the average would be more affected by the idle cell then the wide open cell. A negative value significantly below 128/0% indicates that the fuel system is rich and fuel delivery is being reduced (decreased injector pulse width). A positive value significantly greater than 128/0% indicates that a lean condition exists and the PCM is compensating by adding fuel (increased injector pulse width). When the average of the cells reach a predetermined high or low, a fuel trim DTC will set.
Long Term FT Bn1 and Bn2: Scan Tool Displays Percentage/Counts. Long Term Fuel Trim is derived from the Short Term Fuel Trim value and represents a long-term correction of fuel delivery. A value of 0%/128 indicates that fuel delivery requires no compensation to maintain the PCM commanded air/fuel ratio. A negative value significantly below 0%/128 indicates that the fuel system is rich and fuel delivery is being reduced (decreased injector pulse width). A positive value significantly greater than 0%/128 indicates that a lean condition exists and the PCM is compensating by adding fuel (increased injector pulse width). Because Long Term Fuel Trim tends to follow Short Term Fuel Trim; a value in the negative range due to canister purge at idle should not be considered unusual. Fuel trim values at maximum authority may indicate an excessively rich or lean system.
Loop Status: Scan Tool Displays Open or Closed. Closed Loop indicates that the PCM is controlling fuel delivery according to oxygen sensor voltage. In Open Loop, the PCM ignores the oxygen sensor voltage and bases the amount of fuel to be delivered on TP sensor, engine coolant, and MAF sensor inputs only.
Low Res. Signal: Scan Tool Range 0.0-332.7 m/sec. This signal is generated by the ignition control module. This signal indicates the time between low resolution signal pulses. The PCM uses this signal to determine engine position and engine speed.
MAF: Scan Tool Range 0.0-655 gm/s. MAF (Mass Air Flow) is the MAF Input Frequency converted to grams of air per second. This indicates the amount of air entering the engine.
MAP: Scan Tool Range 10-105 kPa/0.00-5.0 Volts. The Manifold Absolute Pressure (MAP) sensor measures the change in the intake manifold pressure from engine load, EGR flow (L99 and LT1 only), and speed changes. As intake manifold pressure increases, intake vacuum decreases resulting in a higher MAP sensor voltage and kPa reading. The MAP sensor signal is used for the following: (1) To monitor intake manifold pressure changes during the EGR flow test (L99 and LT1 only); (2) To update the BARO reading; (3) Enabling factor for several of the diagnostics.
Mileage Since First Failure: Scan Tool Displays km and miles. This parameter indicates the mileage at which a emission Diagnostic Trouble Code failed for the first time. This mileage will be stored in the Freeze Frame and Failure records buffers.
Mileage Since Last Failure: Scan Tool Displays km and miles. This parameter indicates the mileage at the time the PCM detected the last test ran and failed for a DTC that is stored in the Failure Records buffer only.
Mileage Since MIL Request: Scan Tool Displays km and miles. The PCM will store the mileage of the vehicle at the time a MIL has been requested for an emission DTC. This mileage will be stored in the Freeze Frame buffer only.
Misfire Cur. #1 - Misfire Cur. #8: Scan Tool Range 0-255 Counts. The Misfire Current counters increment at a rate according to the number of possible misfires being detected on each cylinder during the last 200 cylinder firing events. The counters may normally display some activity, but the activity should be nearly equal for all the cylinders.
Misfire Failures: Scan Tool Range 0-65535 Counts. Indicates the number of 200 crankshaft revolution sample periods during which the level of misfire was sufficiently high to report a fail.
Misfire Hist. #1 - Misfire Hist. #8: Scan Tool Range 0-65535 Counts. The Misfire History counters display the total level of misfire that has been detected on each cylinder. The Misfire History counters will not update or show any activity until a misfire DTC (P0300) has become active. The Misfire History counters will update every 200 cylinder firing events.
Misfire Passes: Scan Tool Range 0-65535 Counts. Indicates the number of 200 crankshaft revolution sample periods during which the misfire diagnostic reported a pass.
Misfire Per Cycle Status: Scan Tool Displays Prim. Cyl # 0-8 and Sec. Cyl # 0-8. When a multiple misfire occurs, the scan tool will display the cylinder with the most significant misfire under Prim. Cyl. The scan tool will display the least significant misfire under Sec. Cyl.
MPH km/h: Scan Tool Range 0-255 km/h (0-158 mph). The vehicle speed sensor signal is converted into km/h and mph for display.
MSF Rev. Status: Scan Tool Displays Accept or Rejected. The scan tool will display Rejected when the PCM detects a misfire that is out of the normal misfire range. When rejected is displayed, indicates the PCM did not use the last 200 revolution test.
Not Run Counter: Scan Tool Range 0-255 Counts--When a MIL is requested or a history DTC is stored, the PCM will count and store the amount times a diagnostic test did not run. This information will be stored in Freeze Frame buffer only. Only one DTC can be stored in each Freeze Frame and/or Failure Records buffers.
Oil Level: Scan Tool Displays OK or Low (B and D Car Only). This parameter indicates when the engine oil level is low. The scan tool will display Low when the PCM detects the engine oil level is low.
Pass Counter: Scan Tool Range 0-255. When a MIL is requested or a history DTC is stored, the PCM will count and store the amount times a diagnostic test passed. This information will be stored in Freeze Frame buffer. Only one DTC can be stored in the Freeze Frame buffer.
Pass Key Fuel: Scan Tool Displays Disabled or OK (Except Y Car). The Theft Deterrent Fuel Enable circuit is an input from the Vehicle Theft Deterrent Control Module that signals the PCM to enable the injectors if the proper signal is received. The scan tool will normally display OK. If the Vehicle Theft Deterrent Control Module does not send the correct Theft Deterrent Fuel Enable signal to the PCM, the display will switch to DISABLED and the fuel system may be disabled.
PCM Reset: Scan Tool Displays Yes or No. This parameter indicates when an internal PCM reset has occurred. The scan tool will display YES when an internal PCM reset occurred.
PNP: Scan Tool Displays -ROD21 or P-N - - - - -. This parameter will indicate if the transmission gear selector lever is in park or neutral, or the transmission gear selector is in reverse or any forward gear.
PSP Switch: Scan Tool Displays High Press or Normal (B and D Car Only). This parameter indicates when power steering load is present. The scan tool will display High Press when the PCM detects a power steering load is present (Parking Lot Maneuvers).
Reverse Inhibit: Scan Tool Displays Enabled or Disabled (F Car Only). When vehicle speed is below 4 mph, the PCM will enable the reverse inhibit solenoid and the scan tool will indicate Enabled.
Revs W/Misfire: Scan Tool Range 0-200 counts. This parameter displays the amount of misfire within 200 cycles.
ST FT Avg. Bn1 and Bn2: Scan Tool Displays Counts/Percentage. This parameter indicates the average of the short term fuel trim cells. The short term fuel trim cells are rated (Weighted) for the amount of which they are used. For example, an idle cell will be rated higher then a wide open cell. If a fueling malfunction is occurring in the idle cell and the wide open cell, the average would be more affected by the idle cell then the wide open cell. A negative value significantly below 128/0% indicates that the fuel system is rich and fuel delivery is being reduced (decreased injector pulse width). A positive value significantly greater than 128/0% indicates that a lean condition exists and the PCM is compensating by adding fuel (increased injector pulse width). When the average of the cells reach a predetermined high or low, a fuel trim DTC will set.
Shrt Term FT Bn1 and Bn2: Scan Tool Displays Percentage/Counts. Short Term Fuel Trim represents a short-term correction to fuel delivery by the PCM in response to the amount of time the fuel control oxygen sensor voltage spends above or below the 450 mV threshold. If the oxygen sensor voltage has mainly remained less than 450 mV, indicating a lean air/fuel mixture, short term fuel trim will increase into the positive range above 0%/128 and the PCM will add fuel. If the oxygen sensor voltage stays mainly above the threshold, short term fuel trim will decrease below 0%/128 into the negative range while the PCM reduces fuel delivery to compensate for the indicated rich condition. Under certain conditions such as extended idle and high ambient temperatures, canister purge may cause Short Term Fuel Trim to read in the negative range during normal operation. Fuel trim values at maximum authority may indicate an excessively rich or lean system.
Skip Shift Sol.: Scan Tool Displays Enabled or Disabled (F Car Only). When the PCM enables the skip shift solenoid, the scan tool will display Enabled.
Spark: Scan Tool Range -64° to 64°. Displays the amount of spark advance being commanded by the PCM on the IC circuit. The PCM computes the desired spark advance using the following: (1) Engine coolant temperature; (2) Engine speed (RPM); (3) Load; (4) Vehicle speed. This distributor ignition system is a net build distributor (No timing adjustment). All timing adjustments are completed by the PCM.
Start Up ECT: Scan Tool Range -40°C to 151°C (-40°F to 304°F). Indicates the Engine Coolant Temperature at the time that the vehicle was started. Used by the HO2S diagnostic to determine if the last startup was a cold start.
TCC Brake Switch: Scan Tool Displays Applied or Released. This parameter indicates the state of the TCC brake switch circuit input. Open indicates 0.0 voltage input (brake switch open, brake pedal applied). Closed indicates a B+ voltage input (brake switch closed, brake pedal released).
TCC Duty Cycle: Scan Tool Displays Disabled or Enabled. This parameter is the commanded state of the TCC PWM solenoid. The scan tool will indicate Enabled when the commanded state of the solenoid is ON. When the solenoid is not on the scan tool will display Disabled.
TCC Enable: Scan Tool Displays Engaged or Disengaged. Represents the PCM commanded state of the transmission torque converter clutch.
TCC Stator Temp.: Scan Tool Displays Normal or High (B and D Car with LT1). This parameter indicates the state of the TCC fluid temperature switch input. When the PCM detects the transmission temperature above a predetermined temperature, the scan tool will display High.
Total Misfire: Scan Tool Range 0-255. Indicates the total number of cylinder firing events that were detected as being misfires during the last 200 crankshaft revolution sample period.
TP Angle: Scan Tool Range 0%-100%. TP Angle is computed by the PCM from the TP Sensor voltage. TP Angle should display 0% at idle and 100% at wide open throttle.
TP Sensor: Scan Tool Range 0.00-5.00 Volts. This signal is used by the PCM to determine the amount of throttle demanded by the driver. The display should be between 0.36-0.96 volts at idle and greater than 4.0 volts at wide open throttle.
TR Switch: Scan Tool Displays INVALID, PARK/NEUTRAL, REVERSE, DRIVE 4/OD, DRIVE 3/D, DRIVE 2, or DRIVE 1. Trans Range represents the decoded status of the three transmission range pressure switch inputs from the Transmission Range Pressure Switch Assembly. The combination of transmission range inputs indicates the position of the transmission manual valve.
Traction Control: Scan Tool Displays Active or Inactive (If so equipped). When the traction control system is active the scan tool will display Active.
Warm Up Cycles w/o Emis. Faults: Scan Tool Range 0-40. This parameter counts the number of warm up cycles without an emission fault present. The counter will increment to 40 and roll back to 0 unless a fault occurs. If a fault occurs, the counter will revert back to 0 until the fault is corrected. Clearing information with a scan tool or a loss of power to the PCM will also reset the counter to 0.
Warm Up Cycles w/o Non - Emis. Faults: Scan Tool Range 0-40. This parameter counts the number of warm up cycles without a non-emission fault present. The counter will increment to 40 and roll back to 0 unless a fault occurs. If a fault occurs, the counter will revert back to 0 until the fault is corrected. Clearing information with a scan tool or a loss of power to the PCM will also reset the counter to 0.