PCM Charts
A list of each data message displayed on the Tech 1 scan tool will be explained in two groups; "Engine" or "Transmission."TYPICAL TECH 1 DATA DEFINITIONS
This 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 (OBD) System Check" first. Testing and Inspection 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 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.
LOOP STATUS - "Closed Loop" displayed 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 MAP sensor inputs only.
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.
BAROMETRIC PRESSURE (BARO) - The BARO reading displayed is determined from the MAP sensor at ignition "ON," engine "OFF," and WOT conditions. The BARO reading displayed represents barometric pressure and is used to compensate for altitude differences.
THROT POSITION - Used by the PCM to determine the amount of throttle demanded by the driver. Should read .45-.85 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. Testing and Inspection
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."
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 - Idle speed control by timing KS Activity. Tech 1 Displays "YES" or "NO" - Indicates whether or not a knock signal is being detected by the PCM.
FUEL EVAP PURGE - Used to control EVAP canister purge function. 0% indicates the valve is commanded fully closed while 100% indicates that the valve is fully open.
KS RETARD - Indicates the amount of spark advance the PCM is removing from IC in response to the Knock Sensor (KS) signal.
CONVERTER HIGH TEMP - Air fuel ratio enriches from 14.7 to 1 to 12 to 1 to help cool catalytic converter.
4WD LOW SWITCH - Indicates to PCM when driver selects 4WD.
FUEL EVAPORATOR PURGE - Systems use a proportional signal to control the canister purge function. 0% means the CCP valve is completely closed while 100% implies a fully open canister purge valve.
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 - The PCM cycles 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.
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).
1-2 SHIFT SOL - When the transmission in in first or fourth gear, the Tech 1 should display "ON." When the transmission is in second or third gear, the Tech 1 should indicate "OFF."
2-3 SHIFT SOL - When the automatic transmission is in first or second gear, the Tech 1 should indicate "ON." When the transmission is in third or fourth gear, the Tech 1 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 9B mph. Injector pulse width will go to zero.
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."
SHIFT LIGHT - The shift light is used in manual transmissions to indicate the optimum point for upshifting. The PCM uses engine speed, vehicle speed, and engine load to determine the state of the shift light.
TRANS RANGE SW - Tech 1 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).
IDLE AIR CONTROL - Displays the commanded position of the idle air control pintle in counts. 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.
POWER STEERING - The power steering parameter becomes active when the steering wheel is cranked all the way to the left or right by displaying high or low pressure.
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. PROM ID 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.
FUEL CONTROL
Fuel delivery is controlled by the control module system.
The diagnosis of fuel control starts with "Engine Cranks But Will Not Run," CHART A-3.Related Tests, Information and Procedures This chart will test the fuel system and if there is a problem, will lead you to checking the fuel pump relay circuit, diagnosing the injector circuit or diagnosing the fuel system.
Fuel Injector
Testing the fuel injector circuit is in CHART A-3 with additional diagnosis in CHARTS A-4, A-7 and A- 8. Related Tests, Information and Procedures
A fuel injector/poppet nozzle which does not open may cause a "no start" condition. An injector/poppet nozzle which is stuck partly open could cause loss of pressure after sitting so long crank times would be noticed on some engines. Also, dieseling could occur because some fuel could be delivered to the engine after the key is turned "OFF."
Pressure Regulator
Testing the pressure regulator circuit is in CHARTS A-3 and A-6. Related Tests, Information and Procedures
If the pressure regulator in the fuel injection unit supplies pressure which is too low, poor performance could result. If the pressure is too high, unpleasant exhaust odor may result.
Idle Air Control (IAC)
The diagnosis of idle Air Control (IAC) can be found in "Idle Air Control (IAC) Valve."
If the IAC valve is disconnected or connected with the engine running, the idle RPM may be wrong. The IAC valve may be reset by disconnecting negative battery terminal for 10 seconds then reconnect battery cable, turn ignition "ON," engine "OFF" for 5 seconds then turn ignition "OFF" for 10 seconds.
The IAC valve affects the idle characteristics of the engine. If it is open fully, too much air will be allowed in the manifold and idle speed will be high. if it is stuck closed, too little air will be allowed in the manifold, and idle speed will be too low. if it is stuck part way open, the idle may be rough, and will not respond to engine load changes.
Fuel Pump Circuit
Diagnostic Trouble Code (DTC) 54 indicates a failure in the fuel pump circuit.
Two types of fuel pump relays are used. The Utility series uses one type while the Pickup series uses the other type. The relays have the same function, but terminal arrangement is different. The relays have a terminal to test the fuel pump operation.
The fuel pump prime is a separate terminal located near the relay or in the drivers fenderwell near the fuseable link cluster. By applying voltage at this terminal, it can be determined if the fuel pump will operate. This terminal will also prime the fuel line to the fuel injection unit.
Refer to CHART A-5 for diagnosis of the fuel pump relay circuit. Chart A-5 Fuel Pump Relay Circuit Diagnosis
An inoperative fuel pump will cause a "no start" condition. A fuel pump which does not provide enough pressure can result in poor performance.
An inoperative fuel pump relay can result in long cranking times, particularly if the engine is cold. The oil pressure switch will turn "ON" the fuel pump, as soon as oil pressure reaches about 28 kPa (4 psi).
ENGINE COOLANT TEMPERATURE (ECT) SENSOR
Diagnostic Trouble Code (DTC) 14 or DTC 15 indicates a failure in the engine coolant temperature sensor circuit.
Most scan tools display engine temperature in degrees centigrade. After engine is started, the temperature should rise steadily to about 90°C then stabilize when thermostat opens.
MANIFOLD ABSOLUTE PRESSURE (MAP) SENSOR
Diagnostic Trouble Code (DTC) DTC 33 or DTC 34 indicates a failure in the MAP sensor circuit. Also refer to "MAP Output Check Diagnosis" to check the MAP sensor if there is no DTC. MAP Sensor Output Diagnosis
OXYGEN SENSOR (O2S)
Diagnostic Trouble Code (DTC) 13 indicates an open in the Oxygen Sensor (O2S) circuit. DTC 44 indicates a low voltage in the Oxygen Sensor (O2S) circuit. DTC 45 indicates a high voltage in the Oxygen Sensor (02S) circuit. If a DTC is set, the engine will always run in the "Open Loop" mode. On heated oxygen sensors value will drop lower towards 0 as the sensor heater inside the sensor warms up.
Normal scan voltage varies between 100 mV to 999 mV (.1 and 1.0 volt) while in "Closed Loop." DTC 13 sets in one minute if voltage remains between .35 and .55 volt, but the system will go "Open Loop" in about 15 seconds.
Using the scan tool, observe the long term fuel trim values at different RPM and air flow conditions to determine when DTC 44 or DTC 45 may have been set. If the condition for DTC 44 exists, the long term fuel trim values will be around 150. If the condition for DTC 45 exists, the long term fuel trim values will be around 115.
THROTTLE POSITION (TP) SENSOR
When a Diagnostic Trouble Code (DTC) is set, the PCM will use an artificial value for throttle position and some engine performance will return.
A broken TP sensor can cause intermittent bursts of fuel from the injector(s) and an unstable idle because the PCM thinks the throttle is moving.
A scan tool reads throttle position in volts and should read from .45-.85 volt with the throttle closed, ignition "ON" or at idle. Voltage should increase at a steady rate as throttle is moved toward Wide Open Throttle (WOT).
Scan TP signal while depressing accelerator pedal with engine stopped and ignition "ON." Display should vary from below .85 volt (850 mV) when throttle was closed, to over 4.5 volts (4500 mV) when throttle is held at wide open throttle position.
TP Sensor Output
This check should be performed when TP sensor attaching parts have been replaced. A Tech 1 can be used to read the TP signal output voltage, or:
1. Connect digital voltmeter J 39200 or equivalent, from TP sensor connector terminal "B" (BLK wire) to terminal "C" (DK BLU wire). Jumpers for terminal access can be made using terminals "1214836" and "12014837".
2. With ignition "ON," engine stopped, the TP sensor voltage should be less than .85 volt if more than .85 volt verify free throttle movement. If still more than 1.25 volts, replace TP sensor.
3. Remove the voltmeter and jumpers, reconnect the TP sensor connector to the sensor.
VEHICLE SPEED SENSOR (VSS)
The vehicle speed sensor circuit diagnosis is in the DTC 16 or DTC 24 chart.
Scan tool reading should closely match speedometer readings, with the drive wheels turning.
EGR SYSTEM
Diagnostic Trouble Code (DTC) 32 indicates that there is a failure in the EGR system circuit.
IDLE SPEED
Refer to "Idle Air Control (IAC) Valve" for Idle Air Control (IAC) check.
^ System too lean (high air/fuel ratio) - Idle speed may be too high or too low. Engine speed may vary up and down, disconnecting IAC does not help. May set DTC 44. Scan tool or voltmeter will read an oxygen sensor output less than 300 mV (.3 volt). Check for low regulated fuel pressure or water in fuel. A lean exhaust with an Oxygen Sensor (O2S) output fixed above 800 mV (.8 volt) will be a contaminated sensor, usually silicone. This may also set a DTC 45.
^ System too rich (low air/fuel ratio) - Idle speed too low. Scan counts usually above 80. System obviously rich and may exhibit black exhaust smoke. Scan tool and/or voltmeter will read an Oxygen Sensor (02S) signal fixed above 800 mV (.8 volt).
IGNITION CONTROL (IC)
When the system is running on the ignition control module, that is, no voltage on the bypass line, the ignition control module grounds the Ignition Control (IC) signal. The PCM expects to see no voltage on the IC line during this condition. If it sees a voltage, it sets DTC 42 and will not go into the IC mode.
When the RPM for IC is reached (about 400 RPM), and bypass voltage is applied, the IC should no longer be grounded in the ignition control module so the IC voltage should be varying.
If the bypass line is open or grounded, the ignition control module will not switch to IC mode so the IC voltage will be low and DTC 42 will be set.
If the IC line is grounded, the ignition control module will switch to IC, but because the line is grounded there will be no IC signal. A DTC 42 will be set.
DTC 42 sets if there is an open or a short to ground in the IC or bypass circuit.
KNOCK SENSOR (KS) SYSTEM
DTC 43 sets if there is an open or short to ground in the circuit.
If the conditions for DTC 43 are present, the scan will always display "YES." There should not be a knock at idle unless an internal engine problem, or a system problem exists.
SYSTEM OVER VOLTAGE
DTC 53 sets if there is voltage greater than 17.1 volts for two seconds at PCM terminal "E16." This indicates that there is a basic generator problem.
INTAKE MANIFOLD TUNING VALVE ASSEMBLY
Refer to "Intake Manifold Tuning Valve" Diagnosis.
IGNITION REFERENCE SIGNAL
The ignition reference signal is covered in the "Ignition System."
A/C SIGNAL
Refer to "A/C Clutch Control". A/C Clutch Control
EXHAUST SYSTEM
Refer to "Restricted Exhaust System Check." System Check - Restricted Exhaust