PCM Charts
TYPICAL TECH 1 DATA DEFINITIONSThis information will assist in emission or driveability problems. The displays can be viewed while the vehicle is being driven. Always perform the On-Board Diagnostic System Check first. The "OBD System Check" will confirm proper system operation. The following positions may not be applicable to all engines:
ENGINE SPEED - Engine speed is computed by the Powertrain Control Module (PCM) from the ignition control reference input. It should remain close to desired idle under various engine loads with engine idling.
DESIRED IDLE - The idle speed that is commanded by the PCM. The PCM will compensate for various engine loads to maintain the engine at the desired idle speed.
ENGINE COOLANT TEMP - The Engine Coolant Temperature (ECT) sensor is mounted in the intake manifold and sends engine coolant temperature information to the PCM. The PCM supplies 5 volts to the coolant temperature sensor circuit. The sensor is a thermistor which changes internal resistance as coolant temperature changes. When the sensor is cold (internal resistance high), the PCM monitors a high signal voltage which it interprets 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.
INT AIR TEMP (IAT) - 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 oncoming air density.
MANIFOLD ABSOLUTE PRESSURE (MAP) SENSOR - The Manifold Absolute Pressure (MAP) sensor measures the change in the intake manifold pressure from engine load and speed changes. As intake manifold pressure increases, the air density in the intake manifold also increases and additional fuel is required. The MAP sensor produces a low signal voltage when manifold pressure is low (high vacuum) and a high voltage when the pressure is high (low vacuum). With the ignition ON," and the engine stopped, the manifold pressure is equal to atmospheric pressure and the signal voltage will be high. This information is used by the PCM as an indication of vehicle altitude and is referred to as BARO. Comparison of this BARO reading with a known good vehicle with the same sensor is a good way to check accuracy of a "suspect" sensor. Readings should be the same +/- .4 volt.
BAROMETRIC PRESSURE (BARO) - The BARO reading displayed is determined from the MAP sensor at ignition "ON," engine "OFF," and WOT conditions. This parameter represents a measurement of barometric air pressure and is used in conjunction with Manifold Air Pressure (MAP) to determine manifold vacuum. Since barometric air pressure depends on altitude, it may vary from 100 kPa (sea level) to 60 kPa (14,000 ft.). Both the BARO sensor voltage and the computed pressure are displayed for most vehicles.
THROT POSITION - Used by the PCM to determine the amount of throttle demanded by the driver. Should read .45-.65 volt at idle to above 4 volts at Wide Open Throttle (WOT).
THROTTLE ANGLE - Computed by the PCM from TP sensor voltage (throttle position) and should display 0% at idle and 100% at wide open throttle. Refer to DTC 21 if TP sensor angle is not 0% at idle.
OXYGEN SENSOR (O2S) - Represents the exhaust oxygen sensor output voltage. Should fluctuate constantly within a range between 100 mV (lean exhaust) and 1000 mV (rich exhaust) when operating in "Closed-Loop."
INJECTOR PULSE WIDTH - In this position, the reading is given in milliseconds which is the "on-time" that the PCM is commanding to the injector(s). When engine load is increased, injector pulse width will increase.
SHORT TERM FUEL TRIM (FUEL INTEGRATOR) - Fuel integrator represents a short term correction to fuel delivery by the PCM in response to the amount of time the oxygen sensor voltage spends above or below the 450 mV threshold. If the oxygen sensor voltage has mainly been below 450 mV, indicating a lean air/fuel mixture, fuel integrator will increase to tell the PCM to add fuel. If the oxygen sensor voltage stays mainly above the threshold, the PCM will reduce fuel delivery to compensate for the indicated rich condition.
LONG TERM FUEL TRIM (BLOCK LEARN) - Long term fuel trim is derived from the short term fuel trim value and is used for long term correction of fuel delivery. A value of 128 counts indicates that fuel delivery requires no compensation to maintain a 14.7:1 air/fuel ratio. A value below 128 counts means that the fuel system is too rich and fuel delivery is being reduced (decreased injector pulse width). A value above 128 counts indicates that a lean condition exists and the PCM is compensating by adding fuel (increased injector pulse width).
FUEL TRIM CELL - Fuel trim cell is dependent upon engine speed and MAP sensor readings. A plot of RPM vs. MAP is broken into 16 cells. Fuel trim cell indicates which cell is currently active.
FUEL TRIM ENABLE - If air fuel system is learning (YES) then long term fuel trim is responding to short term fuel trim. If fuel trim enable reads (NO) then long term fuel trim will not respond to change in short term fuel trim normally, learning starts as soon as engine goes into "Closed Loop."
AIR FUEL RATIO - The reading reflects the commanded value. This should be at or near 14.7. A lower number indicates a richer commanded air fuel mixture while a higher number indicates a leaner mixture.
SPARK ADVANCE - This is a display of the spark advance Ignition Control (IC) calculation which the PCM is programming into the ignition system. It computes the desired spark advance using data such as engine temperature, RPM, load, vehicle speed and operating mode.
IDLE SPARK - When enabled this parameter indicates that idle speed is being controlled by IAC and ignition timing.
KS Activity - TECH 1 scan tool Displays "YES" or "NO" - Indicates whether or not a knock signal is being detected by the PCM.
KS RETARD - Indicates the amount of spark advance the PCM is removing from IC in response to the Knock Sensor (KS) signal.
LOOP STATUS - This position will indicate whether the engine control system is operating in "Open" or "Closed Loop." Most systems go "Closed Loop" after a certain amount of run time, when coolant temperature is high enough, and the oxygen sensor becomes active.
CONVERTER HIGH TEMP - Air fuel ratio enriches from 14.7 to 1 to 12 to 1 to help cool catalytic converter.
INTAKE TUNING VALVE - The tuning valve is electrically controlled by the PCM based on RPM and TP sensor inputs, for accurate switching capability at optimum switching points to enable either a "split" or "single" plenum condition.
EGR DESIRED POSITION - The PCM command for EGR valve position that is desired.
EGR ACTUAL POSITION - Current actual EGR position of the EGR valve.
EGR PINTLE POSITION - PCM command for linear EGR valve pintle position that is desired.
EGR DUTY CYCLE - On some systems, a more precise control of Exhaust Gas Recirculation (EGR) is used. This is done by the PCM cycling the EGR valve "ON" and "OFF." The "ON" time (duty cycle) of the EGR solenoid valve, expressed as a percent, determines how much the exhaust gas is recirculated.
1-2 SHIFT SOL - When the transmission in in first or fourth gear, the TECH 1 scan tool should display "ON." When the transmission is in second or third gear, the TECH 1 scan tool should indicate "OFF."
2-3 SHIFT SOL - When the automatic transmission is in first or second gear, the TECH 1 scan tool should indicate "ON." When the transmission is in third or fourth gear, the TECH 1 scan tool should display "OFF."
1-2 SOL/2-3 SOL - An active or inactive command state of the trans solenoid or upshift or downshift.
FUEL SHUTOFF - Used to turn "OFF" the injector driver(s) when RPM is greater than 6350 or mph is greater than 98 mph. Injector pulse width will go to zero.
MPH/km/h - Vehicle speed is a PCM internal parameter. It is computed by timing pulses coming from the Vehicle Speed Sensor (VSS). Vehicle speed is used in checking TCC lock-up speed or speedometer accuracy. Speed is displayed in both Miles Per Hour (mph) and Kilometer Per Hour (km/h).
TCC SOLENOID - In this position, the tool will indicate when the TCC has been commanded by the PCM to turn "ON." This does not necessarily mean that the clutch was engaged but only that the PCM grounded the circuit internally. The best way to determine if the clutch has engaged is to monitor engine RPM when the TCC comes "ON."
TRANS RANGE SW - TECH 1 scan tool displays Park/Neutral, Reverse, Drive 4, Drive 3, Drive 2, Low and Invalid - These values represent the decoded sequence of the Transmission Range (TR) pressure switch assembly circuits and are used to determine manual valve position.
A/B/C RANGE - "ON/OFF," they are used to detect which gear has been manually selected, engine must be operating.
TCC BRAKE SWITCH - This parameter indicates the state of the TCC brake switch circuit input. Open indicates a 0 voltage input (brake switch open, brake pedal applied). Closed indicates a B + voltage input (brake switch closed, brake pedal released). The brake switch is operated by brake pedal travel. The switch is normally closed when the brake is released. This applies battery voltage to the PCM signal line. When brakes are applied the PCM receives a zero (0) volt signal on the signal line which caused TCC to be released. Brake switch input is used for line pressure and TCC control.
IDLE AIR CONTROL - This system is used to control engine idle speed to the desired RPM for different operating conditions. In this mode, the numbers will indicate what position the PCM thinks the valve is in. The PCM moves the IAC in counts and these counts are what is displayed on a TECH 1 scan tool. The greater the number of counts, the greater the idle air passages opened. idle air control should respond fairly quickly to changes in engine load to maintain desired idle RPM.
PARK/NEUTRAL SWITCH - The indication in this mode may vary with manufacturer so the type of reading for a particular tool should be checked in the operator's manual. The important thing is that the reading changes state (switches) when the gear selector is moved from park/neutral to drive or reverse. Engine must be operating.
A/C REQUEST - Displays the state of the A/C signal line to the PCM. Should read "YES" whenever the A/C is requested.
A/C CLUTCH - Displays "ON" when the PCM has commanded the A/C clutch "ON".
SYSTEM VOLTS - Battery/ignition voltage is an analog input signal read by the PCM. It is the ignition switched battery voltage and is mainly used for diagnostics. Certain PCM functions will be modified if the battery voltage falls below or rises above programmed thresholds.
FUEL PUMP VOLTS - This parameter is a reading of the voltage going to the fuel pump. It is used by the PCM as the system voltage. The PCM uses fuel pump volts as a reference.
CALIBRATION ID - The PROM identification parameter describes the particular PROM used in the PCM being tested. The PROM contains the PCM program. Calibration is used when it is necessary to replace the PROM. PROM ID must be specified when ordering new PROMs. PROM ID should not be confused with "Part Number."
TIME FROM START - Time from start is a measure of how long the engine has been running. If the engine stops, time from start will reset to 0:00:00.