Engine Controls - Tests W/codes - PCM Cadillac Seville IV

INTRODUCTION

If no trouble codes were found while performing BASIC TESTING , proceed with self-diagnostics. If no fault codes or only pass codes are present after entering self-diagnostics, proceed to TESTS W/O CODES article in this section for diagnosis by symptom (i.e., ROUGH IDLE, NO START, etc.).

SELF-DIAGNOSTIC SYSTEM

Note. Electronic Control Module (ECM) and Powertrain Control Module (PCM) are same system; terms are often used interchangeably.

Self-diagnostic system consists of 4 components. These components are Powertrain Control Module (PCM), Instrument Panel Cluster (IPC) options, A/C Programmer (ACP) options and Supplemental Inflatable Restraint (SIR) system.

In addition to monitoring a particular set of sensors and switches, PCM maintains continuous communication with each system component. Should a component exceed pre-programmed limits, PCM will recognize a malfunction and may act to control malfunctioning component. To control a particular component, PCM rapidly switches an internal circuit between zero and 5 volts, converting programmed control information into series of pulses that represents coded serial data messages. These messages are transmitted to malfunctioning component, which interprets information and responds accordingly.

As a result, an alphanumeric code, known as a trouble code, is often set in PCM memory. This trouble code identifies malfunctioning component and can be accessed by a service technician as an aid to diagnostic procedures. All trouble codes are displayed on Driver Information Center (DIC) panel.

In addition to monitoring self-diagnostic system and displaying trouble codes, PCM can be programmed by service technician to perform specific diagnostic tests on individual components and systems. Results of these tests are displayed on DIC. This article covers accessing PCM trouble codes and programming self-diagnostic system to perform specific diagnostic tests on system components.

ENTERING SELF-DIAGNOSTICS

1. Turn ignition on. Simultaneously push OFF and WARMER buttons on Climate Control Panel (CCP). Continue pushing OFF and WARMER buttons until segment check appears (about 3 seconds) on Instrument Panel Control (IPC). NOTE: Failure of any segment to glow may result in inaccurate test results. Replace any inoperative segment display before proceeding with self-diagnostic process.
2. When segment check appears (all segments glow), system has entered into self-diagnostic mode. Release both buttons. Driver Information Center (DIC) will display diagnostic codes. Diagnostic code level displays PCM codes first, followed by IPC, ACP and SIR codes (if so prompted).
3. To proceed to desired level, press and release CCP panel HI (fan up) button for "yes" or LO (fan down) button for "no". Depress LO button to go to next test level (i.e., IPC?, ACP? or SIR?) or depress OFF button to return to next selection in previous test level.
4. To exit diagnostics, press AUTO button on IPC. System will go back to normal vehicle operation.

DISPLAYING TROUBLE CODES

1. Diagnostic code level displays PCM codes first, followed by IPC, ACP and SIR codes (if so prompted). Trouble codes appear in ascending (3-digit) numerical order and are prefixed by "P" (PCM), "I" (IPC), "A" (ACP) or "R". A final digit of either a "C" (current) or "H" (history)" will also be indicated on every code.
2. For complete list of available PCM trouble codes, see PCM TROUBLE CODES table. If no codes are present for a system, a "NO X CODE" message (with X being system, i.e. "P", "I", etc.) will be displayed. If communication line to a component is not operating, a "NO X DATA" message will be displayed, indicating that IPC could not communicate with that system.
3. To continue with system diagnostics, see SERVICE MODE OPERATION. To exit from SERVICE MODE and go back to normal vehicle operation, depress AUTO button on IPC.

PCM TROUBLE CODE DEFINITIONS

STATUS LIGHTS DISPLAY

Upon entering PCM system level of self-diagnostic mode, indicator lights on DIC automatically indicate operational status of TCC, certain emission control components and A/C compressor operation. Operational status of these components is indicated by corresponding status light being on or off. (Scheme 36)

Scheme 36

SERVICE MODE OPERATION

Note. IPC, ACP and SIR systems can also be tested in SERVICE MODE. Only information related to PCM diagnosis is in this article.

After PCM trouble codes have been displayed, SERVICE MODE can be used to exit diagnostics or individually perform other tests on different systems.

Selecting System Level

Following trouble code display, first available system will be displayed (i.e., IPC?). When selecting a system to test, any of following actions may be taken to control display

1. Depressing HI (fan up) button on CCP will select displayed system for testing (i.e., PCM DATA, PCM INPUTS, PCM OUTPUTS, etc.). (Scheme 37)
2. Depressing LO (fan down) button on CCP will display next available system selection (i.e., IPC?, ACP? or SIR?). This allows display to be cycled through all system choices. This list of systems can be repeated following end of system list.
3. Depressing OFF button on CCP will stop system selection process and return display to beginning of PCM trouble code sequence.

Selecting Test Type Level

Selection of PCM DATA, PCM INPUTS, PCM OUTPUTS, PCM OVERRIDES, PCM CLEAR CODES or PCM SNAPSHOT test may be displayed. (Scheme 37) If dashes appear in DIC, test is not valid or test conditions are wrong. While selecting a specific test, any of following actions may be taken to control display

1. Depressing HI (fan up) button on CCP will display a specific output or test parameter for selected test type level (i.e., PCM data parameter PD01, etc.). (Scheme 37)
2. Depressing LO (fan down) button on CCP will display next test type level for system level (i.e., PCM INPUTS?, PCM OUTPUTS?, etc.). (Scheme 37) This allows display to be cycled through all available test type choices. This list of test types can be repeated following display of last test type.
3. Depressing OFF button on CCP will stop test selection process and return display to next system level (i.e., IPC?).

Selecting Clear Codes

Selecting PCM CLEAR CODES test will result in PCM CODES CLEAR message being displayed with selected system name for 3 seconds, indicating all stored trouble codes have been erased from memory. After 3 seconds, display will automatically return to next available test type level (i.e., PCM SNAPSHOT?).

After a code has been cleared, make a complete ignition cycle and possibly a test drive. Ensure code does not reset.

Scheme 37

PCM LOCATION

PCM is located behind right side of dash, above kick panel.

PD01: Throttle Position (TP) Sensor

Display shows degrees of throttle opening from -10 to 90.

PD02: Manifold Air Pressure (MAP)

Sensor reading is displayed in kilopascals (kPa) from 14 to 109. With key on, engine off, MAP value will reflect barometric pressure. Multiply local barometric pressure by 3.386 to obtain MAP value within 2 kPa of displayed value with ignition on. MAP will also vary with altitude.

PD03: Computed Barometric Pressure (BARO)

Reading is displayed in kilopascals (kPa) from 61 to 103. BARO pressure reading is taken with key on and engine off, and is corrected at Wide Open Throttle (WOT). Multiply local barometric pressure by 3.386 kPa to obtain a BARO value within 2 kPa of displayed value. BARO varies with altitude (i.e., sea level 100 kPa, Denver 85 kPa).

PD04: Coolant Temperature Sensor (CTS)

Display shows temperature in degrees Celsius (°C) from -40 to 151.

PD05: Intake Air Temperature (IAT) Sensor

Reading is displayed in degrees Celsius (°C) from -40 to 151.

PD08: Spark Advance

Displayed in degrees BTDC as generated by ignition control signal from PCM. Range of display is zero to 52 degrees. If base timing is properly adjusted (10 degrees BTDC), readings from a timing light or meter should agree.

PD10: Battery State Of Charge

Voltage measured at fuel pump feedback circuit No. 120. Displayed in volts from zero to 25.5.

PD11: Engine Speed (RPM)

Displayed in RPM from zero to 6375.

PD12: Vehicle Speed (MPH)

Displayed in MPH from zero to 255.

PD30: Front Bank Injector Pulse Width

Display shows pulse width for cylinders No. 2, 4, 6 and 8 in milliseconds (ms) from zero to 99.9.

PD31: Rear Bank Injector Pulse Width

Display shows pulse width for cylinders No. 1, 3, 5 and 7 in milliseconds (ms) from zero to 99.9.

PD32: Front Oxygen Sensor Voltage

Display shows volts from zero to 1.16.

PD33: Rear Oxygen Sensor Voltage

Display shows volts from zero to 1.16.

PD34: Front Oxygen Sensor Cross Counts

Display shows counts from zero to 255. Cross count is number of times voltage crosses .45-volt reference in one second.

PD35: Rear Oxygen Sensor Cross Counts

Display shows counts from zero to 255. Cross count is number of times voltage crosses .45-volt reference in one second.

PD36: Front Bank Short Term Fuel Trim

Display shows counts from zero to 255. Normal integrator count position is 128, indicating engine is operating normally. A count greater than 128 indicates time is being added to injector pulse width, increasing amount of fuel to engine. A count of less than 128 indicates time is being subtracted from injector pulse width, reducing amount of fuel to engine to compensate for a rich condition sensed at front oxygen sensor.

PD37: Rear Bank Short Term Fuel Trim

Displayed in counts from zero to 255. Normal integrator count position is 128, indicating engine is operating normally. A count greater than 128 indicates time is being added to injector pulse width, increasing amount of fuel to engine. A count of less than 128 indicates time is being subtracted from injector pulse width, reducing amount of fuel to engine to compensate for a rich condition sensed at rear oxygen sensor.

PD38: Front Bank Long Term Fuel Trim

Displayed in counts from zero to 255. Normal count position for long term fuel trim is 128, indicating engine is operating normally. Long term fuel trim value is based on short term learned value, stored in memory blocks of long term according to MAP and RPM values. A count greater than 128 indicates time is being added to injector pulse width, resulting in more fuel to engine. A count of less than 128 indicates time is being subtracted from injector pulse width, resulting in less fuel to engine.

PD39: Rear Bank Long Term Fuel Trim

Display shows counts from zero to 255. Normal count position long term fuel trim is 128, indicating engine is operating normally. Long term fuel trim value is based on short term learned value, stored in memory blocks of long term memory according to MAP and RPM values. A count greater than 128 indicates time is being added to injector pulse width, resulting in more fuel to engine. A count of less than 128 indicates time is being subtracted from injector pulse width, resulting in less fuel to engine.

PD70: Cruise Control Feedback

Display shows percentage of servo apply as measured by servo position sensor. Zero equals no vacuum and 99 equals full vacuum (full apply).

PD71: PRNDL 1 Status

Display shows status of transaxle range switch for circuits No. 772 and 773, which are inputs "B" and "C" to PCM. Zero indicates switch is closed and one indicates switch is open.

PD72: PRNDL 2 Status

Display shows status of transaxle range switch for circuits No. 771 and 776, which are inputs "A" and "P" to PCM. Zero indicates switch is closed and one indicates switch is open.

PD98: Ignition Cycle Counter

Display shows counts from one to 50. Count increases by one with each on-to-off cycle. When a trouble code sets, counter is set to zero. If trouble code becomes history, counter will increase by one with each key cycle until another code is set or until key has been cycled 50 times, at which point code will be erased.

PD99: PCM Programmable Read Only Memory (PROM) Identification Code

Display shows a 3-digit code identifying PROM portion of MEM-CAL unit.

PCM SPECIFIC INPUT CODES

PCM input selections provide testing of inputs to PCM. Input status is shown on display as HI or LO. Input test status is shown as 0 until PCM sees a transition in state of switch; status then changes from 0 to X, indicating test has been passed.

PI70: Cruise Control Brake Switch

Cruise control switch must be in ON position. Test detects opening and closing of cruise control brake switch at PCM terminal 1C2. (Scheme 38) HI means brake switch is closed and PCM has 12 volts at cruise brake switch input. LO means brake switch is open and PCM has zero volts at input.

PI71: Torque Converter Clutch (TCC) Brake Switch

Test detects opening and closing of TCC brake switch at terminal 1C4 of PCM. (Scheme 38) HI means brake switch is closed and PCM has 12 volts at VCC brake switch input. LO means brake switch is open and PCM has zero volts at its input.

PI72: Throttle Switch

Test detects opening and closing of Idle Speed Control (ISC) nose switch at PCM terminal 2A7. (Scheme 38) HI means throttle switch is open and PCM has 5 volts at throttle switch input. LO means throttle switch is closed and PCM has zero volts at throttle switch input.

PI79

Test is not valid.

PI82: Cruise Control ON/OFF Switch

Test detects opening and closing of CRUISE switch mounted on turn signal lever at terminal 1D2 of PCM. (Scheme 38) To activate test, turn cruise control switch to ON position. HI means ON/OFF switch is in ON position and PCM has 12 volts at cruise enable input. LO means ON/OFF switch is in OFF position and PCM has zero volts at cruise enable input.

PI83: Cruise Control SET/COAST Switch

Test detects closing of SET/COAST switch at PCM terminal 1D3. (Scheme 38) To activate test, depress SET/COAST button. Cruise control switch must be in ON position. HI means SET/COAST button is closed (depressed) and PCM has 12 volts on set/coast input. LO means SET/COAST button is open (not depressed) and PCM has zero volts on set/coast input.

PI84: Cruise Control RESUME/ACCEL Switch

This test detects closing of RESUME/ACCEL switch in turn signal lever at PCM terminal 1C3. (Scheme 38) To activate test, slide RESUME/ACCEL switch. Ensure cruise control switch is in ON position to perform this test. HI means RESUME/ACCEL button is closed (pushed) and PCM has 12 volts on resume/accel input. LO means RESUME/ACCEL button is open (not pushed) and PCM has zero volts on resume/accel input.

PI85: Power Steering Pressure Switch (PSPS)

This input comes from PCM terminal 1C9. HI designates power steering switch is closed and PCM is receiving battery voltage. LO means power steering switch is open and PCM is not receiving battery voltage. X means power steering switch has cycled and passed input test.

Scheme 38

PCM SPECIFIC OUTPUT CODES

Note. All PCM specific output tests are to be performed with key on, engine off.

PCM OUTPUTS option provides ability to cycle PCM-controlled outputs. DIC display identifies solenoid or relay and state PCM is commanding that device. HI indicates solenoid or relay is de-energized and LO indicates solenoid or relay is energized. (Scheme 36)

PO00: No Outputs

No outputs are cycled.

PO01: Canister Purge

Canister purge solenoid will cycle on and off every 4 seconds.

PO02: Torque Converter Clutch (TCC)

TCC solenoid will cycle on and off every 4 seconds.

PO03: EGR Solenoid

EGR solenoid will cycle on and off every 4 seconds.

PO04: AIR Switch

Not used. No outputs are cycled.

PO05: AIR Divert

Not used. No outputs are cycled.

PO06: ISC Motor

Idle Speed Control (ISC) motor will alternately extend plunger for 2 seconds and then retract plunger for 2 seconds.

PO07: Cruise Control Vent

Cruise control vent solenoid. Solenoid will cycle on and off every 4 seconds.

PO08: Cruise Control Vacuum

Cruise control vacuum solenoid will cycle on and off every 4 seconds.

PO10: Shift "A"

Transmission shift solenoid "A" will cycle on and off every 4 seconds.

PO11: Shift "B"

Transmission shift solenoid "B" will cycle on and off every 4 seconds.

PO20: A/C Relay

A/C clutch control relay will cycle on and off every 4 seconds.

PO99: Cycle All Outputs

All previously mentioned outputs are cycled on and off about every 4 seconds.

PCM SPECIFIC OVERRIDE CODES

PCM override feature allows testing of certain system functions regardless of normal program instructions, provided test conditions are met.When a test is selected, current mode of function will be displayed as a percentage on DIC panel. If test conditions are not met, DIC panel will display "==" instead of override value selected.

DIC display will alternate between "--" and normal programmed command. Depressing WARMER button will increase override value and depressing COOLER button will decrease override value. Upon release of button, display may either remain at overridden value or automatically return to normal program control, depending on which function is being overridden. Selection of another override test will cancel current override.

PS00: No Overrides

No overrides are active at this point.

PS01: Torque Converter Clutch (TCC) Solenoid

TCC solenoid is energized by WARMER button and deactivated by COOLER button. DIC will display 99 for on and 00 for off. TCC is only able to be engaged when transaxle is in 3rd or 4th gear.

PS02: EGR Solenoid

EGR valve solenoid is de-energized when WARMER button on CCP is depressed, causing EGR valve to receive a vacuum signal and DIC to display 99. Depressing COOLER button on CCP will energize solenoid, stopping vacuum signal to EGR valve and causing DIC to display 00.

PS03: Idle Speed Control (ISC) Motor

1. Test conditions are vehicle in Park or Neutral, PCM commanding A/C relay off and EGR solenoid de-energized. When ISC motor is stopped, DIC displays 50 and TP sensor reads 4 degrees or less.
2. With engine off, depress WARMER button on CCP. ISC plunger will extend as far as it can and display will read 99. With engine on, "==" will be displayed when WARMER button is depressed.
3. With engine off and transaxle in Park or Neutral, depressing COOLER button on CCP will retract ISC until throttle switch opens and display will read 00. With engine on, ISC will retract to base idle (550 RPM).

PS04: Injector Cutout (Power Balance)

1. Test conditions are engine running, transmission in Park or Neutral and vehicle speed zero. Desired engine RPM should be selected before selecting this override as ISC will stay at a selected RPM.
2. Depressing WARMER button will select an injector and cycle injectors at a rate of one selection (next injector) per second. DIC panel will display injector selected. Depressing COOLER button will cause injector cut-off and DIC panel will display injector 00.

PS05: Fuel Pump Relay

1. Test conditions are transmission in Park or Neutral. With engine running, DIC will display 99. With engine off, DIC will display 00.
2. Depressing COOLER button with engine on and relay off causes DIC panel to display 00. Display will return to 99 when button is released.

PS06: AIR System

Not used. No outputs are cycled.

PS07: Cruise Control Servo

1. Before testing, engine should be run to charge vacuum reservoir. Test conditions are transmission in Park or Neutral and engine off. With no buttons depressed, system remains at selected override.
2. Depressing WARMER button will cause servo to retract. DIC panel display will change from 00 to 99. Depressing COOLER button will cause servo to extend. DIC panel display will change from 99 to 00.

PS08: Cooling Fan Speed

1. Each time COOLER button on CCP is depressed, state of low-speed relay will change. A 1 as left digit indicates relay is energized; a 0 indicates relay is de-energized. To properly energize circuit for low speed operation, DIC should display 10.
2. State of high-speed relay changes each time WARMER button on CCP is depressed. A 1 displayed as right digit indicates relay is energized; a 0 indicates relay is de-energized. To properly energize circuit for high speed operation, DIC should display 11.
3. During testing procedures, both cooling fans will run in high and low speeds. Series, series parallel and parallel relays are energized together to produce high speed.

PS09: Spark Advance

1. Test conditions are transaxle in Park or Neutral and engine running. Calculated advance will be displayed when this test is selected. First time COOLER button on CCP is depressed, PCM will fix spark advance to 10 degrees BTDC; DIC will display 10.
2. By depressing COOLER button a second time, PCM will calculate a 1-2 degree timing retard, to a minimum of zero. Depressing WARMER button will increase spark advance up to maximum advance calculated by PCM. If an advance selected is greater than calculated value, "==" will be displayed.

PS10: Injector Flow

When COOLER button is depressed, display cycles at rate of one (next) injector pulse per second. PCM will energize injector for 50 milliseconds. An individual injector can be tested only once per cycle. To prevent engine damage, engine must be run before flow test for that injector can be performed again.

PS11: Transaxle Shift

1. Test conditions are transaxle in "D4" and vehicle speed less than 65 MPH. This override places transaxle in selected gear until WARMER or COOLER buttons are depressed to change gear selection.
2. PCM will prevent a downshift from 2nd to 1st gear at speeds greater than 30 MPH and from 3rd to 2nd gear at speeds greater than 60 MPH. When no button is depressed, transmission remains at selected override position.
3. Each time COOLER button is depressed, transmission will downshift one gear. DIC will display gear number/position selected.
4. Each time WARMER button is depressed, transmission will upshift one gear. DIC will display gear number/position selected.

PCM CLEAR CODES

If PCM CLEAR CODES option is chosen, PCM will clear all stored PCM trouble codes.

PCM SNAPSHOT

Selection of SNAPSHOT test type while in PCM mode will allow recall of snapshot recorded at time of setting of last PCM trouble code. Additionally, one may trigger setting of a snapshot upon demand. Selecting snapshot (by pushing HI button) while in PCM mode will display PXXX (XXX being 3-digit code that recorded snapshot).

While selecting snapshot, any of following actions may be taken to control display.

1. Depressing OFF button on CCP will stop test type selection process and return display to next available system selection.
2. Depressing LO button will allow scrolling through list of PCM diagnostic codes for which PCM has stored a snapshot. Pressing LO button will result in TAKE PCM SNAPSHOT? display. Responding LO will return test to first POXX SNAPSHOT? display.
3. Depressing HI button will cause PCM SNAP DATA? or PCM SNAP INPUTS? to be displayed and will select that test type. At this point, display is controlled as it would be for non-snapshot data and input displays; however, all values and status information represent memorized vehicle conditions.

PFI CHART C-1 - FUEL SYSTEM CHECK

This test provides a quick analysis of fuel system. This chart then identifies more detailed diagnosis required based on symptoms present.

Scheme 39

Scheme 40

PFI CHART C-2, FUEL PRESSURE CHECK

This test determines if fuel system is providing fuel pressure. Components involved include fuel tank, sender, pump, pipes and hoses, pressure regulator, fuel rail, and injectors. Electrical operation of fuel pump relay is also checked.

Note. Test numbers refer to numbers on diagnostic chart.

1. If fuel pump does not operate with ignition on, diagnose as if a Code P020 is set to determine cause. If fuel pump operates with ignition on, check for an open or clogged fuel filter or fuel line.
2. If fuel pressure is normal, check for proper injector operation.
3. If fuel pressure is too high, pressure regulator is not working properly, or cannot work due to a restriction in fuel return line to fuel tank.
4. Fuel pressure leak down can be caused by faulty pressure regulator, a fuel pump check ball, or a leaking injector. Low fuel pressure that does not leak down can be caused by a faulty pressure regulator or a low output fuel pump.

Scheme 41

Scheme 42

PFI CHART C-3 - FUEL PRESSURE & INJECTOR FLOW

This procedure compares fuel pressure drop when each injector is pulsed for a set amount of time. Since each injector is pulsed the same, fuel pressure drop for each injector should be about the same. Faulty injector can be identified by either too high or too low fuel pressure drop.

Note. Test numbers refer to numbers on diagnostic chart.

1. No fuel pressure drop indicates that injector did not operate. This could be caused by a faulty injector, a blown fuse, wiring problem, or a PCM problem.
2. A substantial injector fuel pressure drop indicates a faulty injector. An injector that has no pressure drop may indicate a wiring or PCM problem.
3. If injector pressure drop indicates normal injector operation, check injector resistance. An injector that is out of specification can cause a driveability condition.

Scheme 43

Scheme 44

PFI CHART C-4 - INJECTOR RESISTANCE CHECK

This procedure determines if injector resistance is within specification. An injector with an out-of-specification resistance will cause intermittent driveability problems or problems that DO NOT show up during an injector flow check.

Note. Test numbers refer to numbers on diagnostic chart.

1. Check injector resistance at engine temperature when condition occurs. Injector resistance will normally increase with increasing temperature. Faulty injectors may measure within specification when cold, but not when hot.
2. Injector resistance and flow checks are okay. PFI CHART C-5, POWER BALANCE TEST may indicate possible ignition problem.

Scheme 45

PFI CHART C-5 - POWER BALANCE TEST

This test checks performance of each cylinder by comparing it to other cylinders. PCM shuts off fuel for a given cylinder in its intake cycle. This measures performance of that cylinder by amount of RPM drop caused by that cylinder not producing a power stroke.

Note. Test numbers refer to numbers on diagnostic chart.

1. Idle quality should get worse when an injector is disabled. Engine should miss and idle will become rough.
2. Unequal performance of cylinders during this check indicates an ignition or mechanical problem, assuming fuel system has already been checked. Diagnose ignition system before checking for an engine mechanical problem.
3. If fuel system and power balance checks okay, check EGR, EVAP or PCV system for possible problem.

Scheme 46

PFI CHART C-6 - FUEL LEAK/ODOR CHECK

This procedure provides a means of identifying a fuel system component that is causing a leak. This check also provides information on how to diagnose a fuel odor condition.

Note. Test numbers refer to numbers on diagnostic chart.

1. Vehicle should be operated under same conditions as when leak/odor occurred.
2. Nylon fuel lines are not repairable and must be replaced.
3. EVAP system problem or a rich engine operation may cause a fuel odor condition.

Scheme 47

PFI CHART C-7 - IDLE SPEED CONTROL (ISC) CHECK

This test verifies ISC motor operation and checks ISC plunger adjustment.

Note. Test numbers refer to numbers on diagnostic chart.

1. This checks for a high minimum air idle which could cause a sail-on condition. Minimum air idle should be 450-500 RPM.
2. Perform PCM Code P030 diagnosis to identify cause of faulty ISC motor.
3. This determines ISC motor ability to reach maximum extension. At maximum extension, PCM data PD01 will read 13.0-13.8 degrees if ISC does not adjust to within range.
4. TP sensor idle learn procedure must be performed after ISC plunger adjustment.

Scheme 48

Scheme 49

POWERTRAIN CHART 1 - POWERTRAIN SYSTEM CHECK

POWERTRAIN SYSTEM CHECK is an organized approach to identifying a computer-controlled electronics problem. Understanding chart and using it correctly will reduce diagnostic time and prevent unnecessary parts replacement.

Use POWERTRAIN SYSTEM CHECK to begin diagnosis if any customer complaint does not directly relate to a specific subsystem. If SERVICE ENGINE SOON light fails to glow during cranking, problem could be in PCM power supply circuit. POWERTRAIN SYSTEM CHECK will direct technician to an appropriate diagnostic chart, test procedure or article.

If DIC panel display is not operating properly, PCM computer self-diagnostics mode cannot be used and POWERTRAIN SYSTEM CHECK will direct technician to an appropriate diagnostic chart, test procedure or article.

If a trouble code is identified by PCM computer system self-diagnostics mode, problem can be corrected following appropriate numbered code charts. If no trouble code has been identified, POWERTRAIN SYSTEM CHECK will direct technician to an appropriate diagnostic chart, test procedure of article.

Note. Test numbers refer to numbers on diagnostic chart.

1. Checks if system will enter diagnostics. If diagnostics cannot be entered or displays are blank, problem exists in IPC or related circuit. Diagnose system as follows: Turn ignition on. Using a DVOM connected to ground, backprobe IPC connector cavities A1, A2, C12 and C14. Reading should be greater than 10 volts. If voltage reading on one or more terminal is not as specified, repair open or short in related circuit. If voltage reading is not as specified on all terminals, check charging system. If all of voltage readings are correct, turn ignition off. Disconnect IPC connectors (Black and White). Measure resistance between ground and IPC connector cavities A5 and C16. If any measurement is greater than one ohm, repair affected circuit or check/repair ground. If both circuits are within 0-1 ohm, reconnect IPC connectors. Turn ignition on. Using a DVOM connected to ground, backprobe IPC connector cavity B2. If reading is 14 volts or greater, check IPC connectors for good terminal contact. If contacts are okay and diagnostics still cannot be entered, replace IPC. If reading is less than 14 volts, disconnect radio head and measure voltage at IPC connector terminal B2. If reading is 14 volts or greater, replace radio head. If reading is less than 14 volts, disconnect IPC connector. Check continuity between IPC connector terminal B2 and ground. If continuity is present, repair short in circuit. If continuity is not present, replace IPC assembly.
2. Checks to see if IPC is able to communicate with PCM. If IPC is unable to communicate with PCM, Code I034 will set or NO PCM DATA message will be displayed when diagnostics are used.
3. SERVICE ENGINE SOON light should be on when vehicle is in diagnostic mode.
4. Checks if powertrain system is operational.
5. Checks if PCM codes are present.
6. SERVICE ENGINE SOON light should be off if codes are not present.
7. Checks if known customer complaint is causing problem.
8. If complaint is not in customer complaint list, perform system check applying to situation.

Scheme 50

Scheme 51

POWERTRAIN CHART 2 - PCM POWER & GROUND CHECK

Battery voltage is present at all times at PCM terminals No. 2B1 and 1C16 through circuit No. 480 from engine compartment fuse block, fuse B13. PCM is also fed IGN 1 (hot in run, bulb test and start) at PCM terminal No. 2A6 through circuit No. 1276 from engine compartment fuse block, fuse A9. PCM needs both battery and IGN 1 voltage to operate.

PCM grounding points are at PCM terminals No. 1D1, 1D6, 1D7 and 2A12 through circuit No. 450 to ground (circuit No. G301).

Note. Test numbers refer to numbers on diagnostic chart.

1. This test checks for data line codes that would indicate that entire data line is down.
2. Checks for battery voltage on circuit No. 480. If voltage is measured at one terminal and not other, check circuit No. 480 for an open to connector C101. If voltage is not measured at either terminal, check fuse B13 and circuit No. 480 to C101 for an open.
3. Checks circuit No. 1276 and fuse A9 for open.
4. Checks for open circuit at circuit No. 450. If voltage measures greater than .1 volt on 1-3 wires, repair open to circuit No. S214. If voltage measures greater than .1 volt on all 4 wires, repair open from circuit S214 to G301 (ground).
5. Checks for an open in circuit No. 450 or inside PCM.

Scheme 52

POWERTRAIN CHART 3 - POWERTRAIN GROUND CHECK

Circuit G401 is ground location for fuel pump. Circuit G104 is cooling fan and A/C compressor clutch ground. Circuit G301 is ground for all powertrain electronics, including PCM.

Loose or poor ground connections may cause a variety of problems, including flickering telltales, PCM codes and several driveability problems. POWERTRAIN GROUND CHECK should be performed when referred to by other diagnostics or when erratic or intermittent problem is present.

These 3 vehicle grounds are essential for proper powertrain system operation. They are

1. Circuit G301, located on upper portion of right side kick panel.
2. Circuit G104, located on right side of starter.
3. Circuit G401, located on front side of left rear seat diagonal brace.

Scheme 53

Scheme 54

Scheme 55

Scheme 56

POWERTRAIN CHART 4 - SERVICE ENGINE SOON LIGHT INOPERATIVE

PCM controls SERVICE ENGINE SOON light through circuit No. 419. Light is on when PCM has detected a problem that will affect vehicle emissions or may cause powertrain damage or driveability problems.

SERVICE ENGINE SOON light will glow when certain PCM trouble code(s) are present or when system is in diagnostic mode.

SERVICE ENGINE SOON light will not glow when ignition is on and engine is not running or when engine is running and no PCM code are current; some codes are stored without activating SERVICE ENGINE SOON light.

Note. Test numbers refer to numbers on diagnostic chart.

1. Checks if SERVICE ENGINE SOON light circuit is okay and PCM is unable to control output.
2. This test checks circuit No. 419 for open.
3. Checks for an open in circuit No. 39 or inside PCM.

Scheme 57

POWERTRAIN CHART 5 - SERVICE ENGINE SOON LIGHT ON (NO CODES PRESENT)

PCM controls SERVICE ENGINE SOON light through circuit No. 419. Light will glow when PCM detects a problem that will affect vehicle emissions, or cause powertrain damage or driveability problems.

SERVICE ENGINE SOON light will glow when certain PCM trouble codes are present or when system is in diagnostic mode.

SERVICE ENGINE SOON light will not glow when ignition is on and engine is not running or when engine is running and no PCM code are current; some codes are stored without activating SERVICE ENGINE SOON light.

Note. Test numbers refer to numbers on diagnostic chart.

1. With ignition on, SERVICE ENGINE SOON light should be off. Check if any other fault is present.
2. Check for diagnostic trouble code(s) causing SERVICE ENGINE SOON light to glow.
3. If SERVICE ENGINE SOON light goes off when PCM connector 2A/2B is disconnected, replace PCM. If SERVICE ENGINE SOON light stays on when PCM connector 2A/2B is disconnected, repair circuit No. 419 for a short to ground.

Scheme 58

POWERTRAIN CHART 6 - MULTIPLE PCM CODES

Some powertrain components share common feeds and returns. Certain failures of these circuits will cause multiple codes to set. Flow chart indicates groups of codes set by failure of common feeds and/or returns. If all codes in a group are set, perform diagnosis listed in that box. If all codes in a group are not set, diagnose lowest code number first.

Note. Test numbers refer to numbers on diagnostic chart.

1. Circuit No. 474 is 5-volt feed from PCM to MAP and TP sensors. An open or short to ground in circuit No. 474 between PCM terminal 1C14 and circuit S215 will cause Codes P022 and P032 to set.
2. Circuit No. 476 is sensor return to PCM from IAT and MAP sensors. An open in circuit No. 476 between circuit S216 and PCM terminal 2A5 will cause Codes P031 and P038 to set.
3. Circuit No. 1076 is sensor return to PCM from ECT and TP sensors. An open in circuit No. 1076 between circuit S217 and PCM will cause Codes P015 and P021 to set.
4. Circuit No. 750 is battery feed, from engine compartment fuse block fuse D1 to TCC brake switch, which feeds TCC through circuit No. 420. An open in circuit No. 420 or 750, or an open in TCC brake switch, will set Code P039 or P090.

Scheme 59

Scheme 60

POWERTRAIN CHART 7 - REAR OXYGEN SENSOR DIAGNOSIS

PCM provides .45-volt reference signal to oxygen sensor on circuit No. 412. When warm, a properly operating oxygen sensor will drive .45-volt reference signal lower, indicating a lean mixture or higher, indicating a rich mixture. This signal will toggle from rich to lean rapidly, at least one toggle every 2 seconds, if PCM is in good control of air/fuel mixture.

This chart is designed to be used after oxygen sensor circuit and PCM operation have been verified through POWERTRAIN CHART 1, POWERTRAIN SYSTEM CHECK and PCM diagnostic trouble code diagnosis.

This chart should identify oxygen sensors that are open (not able to drive .45-volt reference signal) or shorted (sensor output is fixed high or low, due to contaminants or internal sensor faults).

Note. Test numbers refer to numbers on diagnostic chart.

1. With engine running and coolant at normal operating temperature (85°C or greater) and at fast idle, observe engine data parameter PD33. Voltage should swing from less than .3 volt to greater than .6 volt.
2. With engine at fast idle, observe open/closed loop status light (AUTO indicator on CCP). If PCM switches system into closed loop operation, oxygen sensor is okay. If PCM remains in open loop operation and coolant temperature PD04 is greater than 85°C, replace oxygen sensor.
3. If voltage remains between .3-.6 volt for a minimum of one minute, replace oxygen sensor and check for cause of sensor contamination.
4. If there is no high voltage variation, check sensor for intermittent terminal contact or faulty sensor.

Scheme 61

Scheme 62

POWERTRAIN CHART 8 - FRONT OXYGEN SENSOR DIAGNOSIS

PCM provides .45-volt reference signal to oxygen sensor on circuit No. 1589. When warm, a properly operating oxygen sensor will drive .45-volt reference signal lower, indicating a lean mixture or higher, indicating a rich mixture. This signal will toggle from rich to lean rapidly, at least one toggle every 2 seconds, if PCM is in good control of air/fuel mixture.

This chart is designed to be used after oxygen sensor circuit and PCM operation have been verified through POWERTRAIN CHART 1, POWERTRAIN SYSTEM CHECK and PCM diagnostic trouble code diagnosis.

This chart should identify oxygen sensors that are open (not able to drive .45-volt reference signal) or shorted (sensor output is fixed high or low, due to contaminants or internal sensor faults).

Note. Test numbers refer to numbers on diagnostic chart.

1. With engine running and coolant at normal operating temperature (85°C or greater) and at fast idle, observe engine data parameter PD32. Voltage should swing from less than .3 volt to greater than .6 volt.
2. With engine at fast idle, observe open/closed loop status light (AUTO indicator on CCP). If PCM switches system into closed loop operation, oxygen sensor is okay. If PCM remains in open loop operation and coolant temperature PD04 is greater than 85°C, replace oxygen sensor.
3. If voltage remains between .3-.6 volt for a minimum of one minute, replace oxygen sensor and check for cause of sensor contamination.
4. If there is no voltage variation, check sensor for intermittent terminal contact or faulty sensor.

Scheme 63

PCM CODE P012 - NO DISTRIBUTOR (TACH) SIGNAL

PCM checks for CAM HI pulses being received without REF HI (distributor) reference pulses. If PCM senses no reference pulses, engine will not start because fuel delivery system is triggered by pulses and Code P012 is set.

Possible causes of "no distributor reference signal" are

1. Open or short in circuit No. 430 from ignition control module to PCM.
2. Ignition control module is unable to process pick-up coil signals to produce distributor reference pulses.
3. Grounding screw is located on metal tab attached to plastic fitting on 5-wire harness.

Test Conditions

PCM Code P041 not set. Code P041 is tested anytime cam position sensor signals are being received during engine cranking operation.

Failure Conditions

If PCM does not see distributor reference pulses (REF HI) for 4 seconds with cam position sensor pulses (CAM HI) being received, PCM Code P012 will be set.

Action

PCM turns on SERVICE ENGINE SOON light.

Note. Test numbers refer to numbers on diagnostic chart.

1. This checks for proper output of ignition system. If voltmeter reads 0.5-2.8 volts, ignition control module is receiving pick-up coil signal and producing reference pulses.
2. This checks for proper ground connections between PCM and engine, and between PCM and ignition control module.
3. This checks for proper voltage through circuit No. 430 from ignition coil to PCM. If PCM terminal 1D8 sees 0.5-2.8 volts, PCM is receiving reference pulses.
4. If ignition system will produce spark, fault is not within pick-up coil or ignition control module.

Note On Intermittents

If PCM Code P012 is stored as a history code, start engine and allow it to idle. Manipulate circuits No. 430 and 453. An intermittent open will cause engine to stumble or stall when PCM loses distributor reference. If wiring and PCM connectors are okay, check ignition pick-up coil leads for intermittent open circuit.

Scheme 64

Scheme 65

PCM CODE P013 - REAR OXYGEN SENSOR NOT READY

PCM provides .45-volt reference signal to oxygen sensor on circuit No. 412. When sensor reaches operating temperature, it will generate a counter voltage that will vary based on amount of oxygen in exhaust. Rear oxygen sensor is located in manifold, before catalytic converter.

A lean exhaust will generate a low voltage and cause .45-volt reference signal to decrease. A rich exhaust will generate a higher voltage and cause .45-volt reference signal to increase.

Code P013 will set when oxygen sensor cannot respond under test conditions and generate a voltage greater or less than .45-volt reference.

Code P013 will also set under following conditions

1. Open in circuit No. 412 or 413.
2. Short to voltage on circuit No. 412 or 413.
3. Faulty oxygen sensor.

PCM Codes P014, P015, P021, P022, P026 and P027 are not set. Coolant temperature greater than or equal to 180°F (82°C). TP sensor value of 5-30 degrees. Throttle switch open. RPM 800 or greater.

Oxygen sensor voltage stays .307-.609 volt for more than 64 seconds (not toggling).

PCM turns on SERVICE ENGINE SOON light and closed loop is disabled. PCM enables canister purge solenoid if Code P017 is set.

Note. Test numbers refer to numbers on diagnostic chart. See POWERTRAIN CHARTS for references to CHART 7.

1. Voltage on PCM data parameter PD33 should fluctuate from less than 0.3 volt to greater than 0.6 volt. If voltage remain greater than 0.6 volt, check circuit No. 412 for short to voltage. If voltage remains less than 0.3 volt, check circuit No. 412 for short to ground.
2. Measuring voltage using voltmeter will isolate sensor/wiring problem from a PCM problem. If voltage fluctuates at greater than 0.6 volt and less than 0.3 volt, fault is with PCM. If voltage remains less than 0.3 volt, check circuit No. 412 for short to ground or circuit No. 413 for short to voltage. If voltage remains greater than 0.6 volt, check circuit No. 412 for short to voltage. If voltage remains 0.3-0.6 volt, check circuits No. 412 and 413 for an open.

Scheme 66

Scheme 67

PCM CODE P014 - SHORTED COOLANT SENSOR SIGNAL

Coolant sensor is located on thermostat housing. Sensor signal is on circuit No. 410; sensor ground is on circuit No. 1076. As sensor temperature increases, resistance decreases. A high coolant temperature will result in low signal voltage on circuit No. 410. Code P014 sets because coolant temperature cannot be greater than 296°F (147°C) when intake air temperature is less than 212°F (100°C).

PCM Codes P037 and P038 are not set and intake air temperature sensor value is less than or equal to 212°F (100°C).

Coolant sensor value greater than or equal to 298°F (148°C) for 2 seconds.

PCM turns on SERVICE ENGINE SOON light and uses IAT sensor value instead of coolant sensor value for all calculations during first 10 minutes of operation; it then uses a value of 194°F (90°C).

Note. Test numbers refer to numbers on diagnostic chart.

1. With coolant sensor or wiring shorted, PCM parameter PD04 should indicate 298°F (148°C) or greater. If PD04 does not indicate 298°F (148°C) or greater, sensor or wiring is not shorted. See NOTE ON INTERMITTENTS.
2. Checks for shorted sensor or circuit No. 410. If parameter value stays at 142°C or greater with sensor unplugged, short is in circuit No. 410 between terminal "A" and PCM terminal 3E16.
3. Fault is most likely at PCM connector or PCM.

Manipulate wiring on circuit No. 410, coolant sensor and PCM connector while observing PCM parameter PD04. If failure is induced, coolant temperature will jump from its normal value to shorted reading of 148°C or greater. Disconnect and reconnect coolant sensor and PCM connectors, and ensure they properly latch. If wiring and connectors are okay, substitute a known good sensor, and retest.

Scheme 68

Scheme 69

PCM CODE P015 - OPEN COOLANT SENSOR SIGNAL

Coolant sensor is a 2-wire thermistor, whose resistance varies with temperature. Sensor signal is on circuit No. 410; sensor ground is on circuit No. 1076.

As sensor temperature increases, sensor resistance decreases. High coolant temperature will result in low signal voltage on circuit No. 410. PCM Code P015 sets because PCM assumes coolant temperature cannot be -36°F (-38°C) or less when IAT is 4.4°F (-20°C) or greater.

PCM Codes P037 and P038 not set and IAT sensor value greater than or equal to 4.4°F (-20°C).

Coolant sensor value is -36°F (-38°C) or less for 2 seconds.

PCM turns on SERVICE ENGINE SOON light and uses IAT sensor value instead of coolant sensor value for all calculations during first 10 minutes of operation. After 10 minutes, PCM uses a value of 194°F (90°C).

Note. Test numbers refer to numbers on diagnostic chart.

1. If sensor or wiring is open, parameter PD04 should indicate -38°C or less. If PD04 does not indicate -38°C or less, sensor signal is not open. See NOTE ON INTERMITTENTS.
2. This checks for open sensor signal in circuit No. 410 from PCM to sensor connector. If parameter PD04 indicates 148-151°C with connector shorted, circuits No. 410 and 1076 are okay.
3. Checks for open in circuit No. 1076 from sensor terminal "B". If shorting terminal "B" to ground causes parameter PD04 to indicate 148-151°C, an open in circuit No. 1076 exists.
4. This checks if PCM can recognize a short to ground or low voltage on terminal 3E16, coolant temperature signal. If grounding terminal 3E16 causes PD04 to indicate 148-151°C, circuit No. 410 from PCM to coolant sensor is open.
5. Fault is most likely at PCM connector or PCM.

Manipulate wiring on circuits No. 410 and 1076 (coolant temperature sensor and PCM connector) while observing PCM parameter PD04. If failure is induced, coolant temperature will jump from normal value to open reading (-38°C or less). Repair intermittent open on circuit No. 410 or 1076. Disconnect and reconnect coolant sensor and PCM connectors, and ensure they properly latch. If wiring and connectors are okay, substitute a known good sensor, and retest.

Scheme 70

PCM CODE P016 - ALTERNATOR VOLTAGE OUT OF RANGE

PCM monitors ignition voltage on circuit No. 1276 to PCM. PCM Code P016 sets when system voltage drops to less than 10 volts or increases to greater than 16 volts with engine running at greater than 500 RPM. If ignition voltage goes to zero volt (open circuit), vehicle will not run since PCM does not have ignition signal.

Engine speed greater than or equal to 500 RPM.

Ignition voltage to PCM less than 10 volts or more than 16 volts for 5.3 seconds.

PCM turns on SERVICE VEHICLE SOON light. PCM turns off canister purge solenoid, disables cruise control and de-energizes TCC solenoid, EGR solenoid and long term fuel trim.

Note. Test numbers refer to numbers on diagnostic chart.

1. This checks PCM data for parameter PD10. If voltage is 16 volts or greater, alternator is not controlling voltage.
2. This checks for proper charging system operation.
3. This checks for proper charging system operation with electrical loads on alternator.

PCM Code P016 may be stored as a history code if battery charge was low. Load test battery, and check for proper operation of charging system. Check for loose battery cable connection at starter motor.

Scheme 71

Scheme 72

PCM CODE P017 - FRONT OXYGEN SENSOR NOT READY

When warm, a properly operating oxygen sensor will provide PCM .45-volt reference signal lower (less than .45 volt) to indicate a lean mixture and higher ( more than .45 volt) to indicate a rich mixture. If oxygen sensor does not vary from cold or not-ready voltage under test conditions, PCM assumes sensor cannot respond to air/fuel mixture changes and sets a PCM Code P017.

Possible causes of PCM Code P017 are

1. Open in circuit No. 1589 or 413.
2. Short to voltage on circuit No. 1589 or 413.
3. Oxygen sensor cannot respond.

PCM Codes P014, P015, P021, P022, P026 and P027 not set. Coolant temperature more than or equal to 180°F (82°C). TP sensor value 5-30 degrees. Throttle switch open. RPM 800 or more.

Oxygen sensor voltage stays .307-.609 volt for more than 64 seconds (not toggling).

PCM turns on SERVICE ENGINE SOON light. PCM enables canister purge solenoid if Code P013 is also set. Closed loop operation is disabled.

Note. Test numbers refer to numbers on diagnostic chart. See POWERTRAIN CHARTS for references to CHART 8.

Scheme 73

1. Voltage on PCM data parameter PD32 should fluctuate at greater than 0.6 volt and less than 0.3 volt. If voltage remains at greater than 0.6 volt, check circuit No. 1589 for a short to voltage. If voltage remains at less than 0.3 volt, check circuit No. 1589 for a short to ground.
2. Measuring voltage using a voltmeter will isolate a sensor/wiring problem from a PCM problem. If voltage fluctuates at greater than 0.6 volt and less than 0.3 volt, PCM is faulty. If voltage remains at less than 0.3 volt, check circuit No. 1589 for a short to ground or circuit No. 413 for a short to voltage. If voltage remains at greater than 0.6 volts, check circuit No. 1589 for short to voltage. If voltage remains 0.3-0.6 volt, check circuits No. 413 and 1589 for an open.

PCM CODE P019 - SHORTED FUEL PUMP FEEDBACK SIGNAL

PCM monitors fuel pump feedback voltage for 4 seconds after ignition is turned on without engine being cranked. Fuel pump relay will be energized for 2 seconds and then de-energized. If voltage on fuel pump feedback does not drop to less than 7 volts during first 4 seconds after ignition is turned on (engine off), PCM Code P019 will set, indicating voltage on circuit No. 120 with fuel pump relay de-energized.

PCM Code P012 not set. Coolant temperature at 122°F (50°C) or greater. No distributor reference pulses detected since ignition was turned on.

Fuel pump feedback voltage remains greater than or equal to 7 volts for 4 seconds (fuel pump relay never de-energized).

PCM turns on SERVICE VEHICLE SOON message.

Note. Test numbers refer to numbers on diagnostic chart.

1. With ignition on, engine off, fuel pump should not be running and fuel pump feedback (PCM parameter PD10) should be zero volts. If PD10 shows voltage greater than 7 volts, repair circuit No. 120.
2. This checks for shorted oil pressure switch contacts powering fuel pump at all times. A shorted oil pressure switch will cause PCM Code P019 to set.
3. This checks for shorted fuel pump relay.
4. This checks for voltage on circuit No. 120 at PCM.
5. This checks for proper control of fuel pump relay by PCM.

Probe fuel pump test point using a voltmeter to ground. Turn ignition on, and observe voltmeter. Voltmeter should indicate battery voltage for 2 seconds and then drop to zero. If voltage reading stays at battery voltage for longer than 2 seconds, check for sticking fuel pump relay contacts. Repeat test several times. Continue probing fuel pump test point to ground. Start engine, and then turn it off. Voltage should immediately drop to zero. If voltage does not immediately drop to zero, check oil pressure switch contacts.

Scheme 74

Scheme 75

PCM CODE P020 - OPEN FUEL PUMP CIRCUIT (1 OF 3)

PCM Code P020 is set when PCM sees fuel pump is not energized (zero volts on feedback circuit) with engine cranking or running. PCM code is designed to detect a fuel pump relay fault (relay not powering fuel pump).

Engine speed greater than or equal to 24 RPM.

Fuel pump feedback voltage less than or equal to 2 volts for 1.3 seconds or more.

PCM turns on SERVICE VEHICLE SOON light.

Note. Test numbers refer to numbers on diagnostic chart.

1. Checks for engine to start with fuel pump powered through fuel pump relay. If engine does not start, proceed to PCM CODE P020 (2 OF 3).
2. Zero volts with engine running indicates an open from fuel pump power circuit to PCM. Fuel pump relay is not at fault.

Notes On Intermittents

If PCM Code P020 is stored as history code, unplug oil pressure switch. Start engine and allow to idle. Check relay for proper installation into socket. Manipulate affected wiring. If fault is induced, engine will stall and Code P020 will set. If Code P020 sets without engine stalling, check for intermittent open in circuit No. 120 between PCM terminal 3E13 and splice to fuel pump relay "A" terminal No. 3.

Scheme 76

PCM CODE P020 - OPEN FUEL PUMP CIRCUIT (2 OF 3)

Note. Test numbers refer to numbers on diagnostic chart.

Scheme 77

1. 3) Checks for proper control of fuel pump relay by PCM.
2. 4) Checks for open from fuel pump fuse to relay terminal No. 5.
3. 5) Checks for open from relay terminal No. 2 to ground.
4. 6) Checks continuity for complete fuel pump circuit from fuse A1 through fuel pump windings to ground. Using a DVOM to jumper contact cavities of relay connector, DVOM should read greater than 10 volts if circuit is okay. If circuit is okay, fuel pump relay is faulty.
5. 7) If relay or relay drive circuits are grounded, PCM may be damaged by excessive current draw if battery voltage is greater than 16 volts. Repair fault, and check for proper operation.
6. 8) Fault is most likely at PCM connector or PCM. Before replacing PCM, check for damaged terminals or poor connections.
7. 9) Refer to appropriate WIRING DIAGRAM article.

PCM CODE P020 - OPEN FUEL PUMP CIRCUIT (3 OF 3)

Note. Test numbers refer to numbers on diagnostic chart.

1. 10) With ignition on, DVOM should read greater than 10 volts for 2 seconds as relay powers up fuel pump.
2. 11) If a short circuit is present, short may be in circuit No. 120, in fuel pump or in PCM. Normal circuit resistance is 3-4 ohms.
3. 12) If DVOM reads a steady voltage of greater than 10 volts, non-switched portion of fuel pump circuit is shorted.
4. 13) This checks for PCM shorting circuit No. 120 to ground.
5. 14) This checks for short circuit in fuel tank.
6. 15) This checks fuel pump for short circuits. Check harness connector.
7. 16) This checks circuit No. 120 for a short to ground.
8. 17) Check for grounded fuel pump test point, connection at relay center and oil pressure switch. Also check harness for short to ground.

If fuel pump test point is grounded, fuse will blow and PCM Code P020 will set. If necessary, replace fuse. Start engine, and allow it to idle. Manipulate affected wiring and connectors. If fault occurs, fuse will blow and engine will stall.

Scheme 78

PCM CODE P021 - SHORTED TP SENSOR CKT (SIGNAL VOLTAGE HIGH)

Throttle Position (TP) sensor is a potentiometer. A 5-volt reference is provided on circuit No. 474 and ground is provided on circuit No. 1076. TP sensor signal circuit No. 417 varies between zero and 5 volts based on throttle plate position. At low throttle angle, TP sensor signal voltage is low. PCM uses TP sensor information to determine idle, WOT, deceleration leanness and acceleration enrichment. Code P021 sets when PCM detects a TP sensor signal that is too high.

Engine speed 0-6375 RPM.

TP sensor value greater than or equal to 87 degrees for 0.1 second.

PCM turns on SERVICE ENGINE SOON light and disables TCC. PCM sets TP sensor equal to 13 degrees when TP sensor is open and 6 degrees when TP sensor is closed. 3rd and 4th gears are disabled.

Note. Test numbers refer to numbers on diagnostic chart.

1. If TP sensor or wiring is shorted, data parameter PD01 will read 87 or greater.
2. Checks for shorted TP sensor or wiring. Open in circuit No. 1076 will result in high TP sensor signal whenever TP sensor is plugged in.

Scheme 79

PCM CODE P022 - OPEN TP SENSOR CIRCUIT (SIGNAL VOLTAGE LOW)

Throttle Position (TP) sensor is a potentiometer. A 5-volt reference is provided on circuit No. 474 and ground is provided on circuit No. 1076. TP sensor signal circuit No. 417 varies between zero and 5 volts based on throttle plate position. At low throttle angle, TP sensor signal voltage is low. PCM uses TP sensor information to determine idle, WOT, deceleration leanness and acceleration enrichment. PCM Code P022 sets when PCM detects a TP sensor signal that is too low.

Engine speed at least 600 RPM.

TP sensor value less than -5 degrees for one second.

PCM turns on SERVICE ENGINE SOON light and disables TCC. PCM sets TP sensor equal to 13 degrees when throttle switch is open and 6 degrees when throttle switch is closed.

Note. Test numbers refer to numbers on diagnostic chart.

1. If Code P032 is also present, check circuit No. 474 for open or short to ground. TP sensor and MAP sensor share 5-volt reference signal.
2. With TP sensor or wiring open, PCM data parameter PD01 will read -5 or less.
3. Checks for open TP sensor or circuit. If data value stays less than 80 with TP sensor terminals "A" and "C" jumpered together, problem is in wiring.
4. Voltage should be greater than 0.5 volt if circuit No. 474 is not open or shorted to ground.
5. Checks to see if circuit No. 474 is open or shorted to ground.
6. Checks if signal is reaching PCM. If signal is reaching PCM, then fault is in PCM.

Scheme 80

Test Conditions (Crank)

By-pass line low (zero volts) and at least 2 reference pulses have been received by PCM.

Failure Conditions (Crank)

No ignition pulses detected in circuit No. 423.

Test Conditions (Run)

By-pass line high (5 volts) and at least 2 reference pulses have been received by PCM.

Failure Conditions (Run)

No ignition control pulses detected on circuit No. 423.

PCM turns on SERVICE ENGINE SOON light and will not enable spark timing control. Engine will start and run on base timing. PCM disables EGR solenoid.

Note. Test numbers refer to numbers on diagnostic chart.

1. When circuit No. 423 is shorted to ground, engine will have a long crank and hard start condition. When PCM detects grounded circuit, by-pass line will be shifted low.
2. With only distributor reference (distributor reference ground jumpered), engine will run on back-up spark control. This checks for proper ground connections between PCM and engine and between PCM and ignition control module.
3. This ensures PCM provides an ignition control output signal over circuit No. 423.
4. This checks if ignition control module can ground ignition control signal with an open by-pass circuit.
5. This checks if ignition control module can recognize a voltage on by-pass circuit and stop grounding ignition control (PCM-controlled timing).
6. This checks for by-pass signal to module. If by-pass signal is being sent by PCM to ignition control and if module is interpreting by-pass voltage correctly, module will switch off ground to ignition control.
7. Fault may exist in 6-way connector. Check connector and terminals for damage. If connector is okay, plug in connector, and retest for PCM Code P023.

Scheme 81

Scheme 82

PCM CODE P024 - VEHICLE SPEED SENSOR (VSS) CIRCUIT PROBLEM

VSS is a permanent magnet pulse generator mounted in transaxle. PCM uses VSS input for TCC apply-and-release determinations, to select between RPM and throttle angle control of ISC, and as a test condition for many codes. PCM Code P024 sets when PCM detects zero MPH when engine RPM and TP sensor indicate that vehicle is moving.

PCM Codes P021, P022, P026 and P027 not set. Transaxle in Reverse or Drive and brakes not applied. Throttle switch open. Throttle angle greater than 17 degrees. Engine speed at least 1400 RPM.

Vehicle speed equals zero MPH for 3.3 seconds.

PCM turns on SERVICE ENGINE SOON light and disables Torque Converter Clutch (TCC), cruise control and 3rd and 4th gears.

Note. Test number refers to number on diagnostic chart.

1. Vehicle speed sensor provides 0-36 volts AC signal to PCM, depending upon vehicle speed. With tires moving, signal to PCM should be at least .5 volt AC.

Check for Electromagnetic Interference (EMI) induced on circuit No. 400 and 401 by running them close to spark plug wires or high power transmitters (mobile radios) operating in vicinity.

Scheme 83

Scheme 84

Scheme 85

Scheme 86

PCM CODE P026 - SHORTED THROTTLE SWITCH CIRCUIT

Throttle switch is part of ISC motor assembly. PCM provides a 5-volt reference signal on circuit No. 427. When throttle lever contacts ISC plunger, throttle switch closes. When throttle switch is closed, input voltage is low. PCM Code P026 sets when PCM sees a TP sensor signal greater than 20 degrees (accelerator applied) but throttle switch remains closed.

PCM Codes P021 and P022 not set and throttle angle is 20-75 degrees.

Throttle switch input to PCM closed for 1.8 seconds.

PCM turns on SERVICE ENGINE SOON light, disables EGR and assumes throttle switch is closed if brakes are applied or if TP sensor position is less than or equal to 18 degrees. PCM also assumes open throttle when brakes are off or TP sensor position is more than 18 degrees.

Note. Test numbers refer to numbers on diagnostic chart.

1. PCM input P172 should cycle from LO to HI to LO when accelerator is depressed and released.
2. If PCM input P172 changes to HI when ISC motor is disconnected, fault is with ISC motor. If P172 still stays LO, check circuit No. 427 for short to ground.
3. Checks if circuit No. 427 is shorted to ground or if PCM is faulty.

Scheme 87

Scheme 88

PCM CODE P027 - OPEN THROTTLE SWITCH SIGNAL

Diagnostic test monitors ISC throttle position switch during some coast down and idle conditions with throttle position switch open and brake applied. Under these conditions, PCM commands ISC to retract, and monitors TP sensor for corresponding decrease in throttle position. PCM sets Code P027 if it detects a decrease in throttle position 2 times in succession, throttle is resting on ISC plunger and throttle position should be closed.

PCM Codes P021, P022 and P024 not set. Vehicle in coast down condition. Throttle switch open, brakes applied, throttle angle 16.5 degrees or less and RPM greater than desired. At least 6 seconds have passed between brake applications or the last ISC motor pulse from PCM.

PCM retracts ISC motor and sees a corresponding decrease in throttle angle twice.

PCM turns on SERVICE ENGINE SOON light. EGR is disabled.

Note. Test numbers refer to numbers on diagnostic chart.

1. ISC 4-way connector is located at a jumper connector near alternator and cruise control servo.
2. ISC jumper is a separate harness that connects ISC to PCM harness.

Ensure ISC plunger is depressed when throttle linkage contacts stop screw. Check ISC jumper connectors and PCM connector for loose or improperly crimped terminals.

Scheme 89

Scheme 90

Scheme 91

Scheme 92

Scheme 93

Scheme 94

Scheme 95

Scheme 96

Scheme 97

PCM CODE P030 - ISC RPM OUT OF RANGE

PCM controls engine idle RPM by increasing or decreasing throttle opening using Idle Speed Control (ISC) motor. ISC controls idle speed any time throttle switch is closed. PCM Code P030 detects engine RPM out of limits.

PCM Codes P021, P022, P024, P026 and P027 not set, throttle switch closed, vehicle speed equals zero, battery voltage greater than or equal to 11 volts, desired engine speed 152 RPM greater than actual RPM, and idle speed control start-up delay over. Engine not receiving power steering load. PCM not commanding an idle speed anticipate.

ISC motor in forward mode. TP sensor at least 14 degrees or less and ISC extending for 30 seconds or ISC motor in reverse mode, TP sensor position at 2 degrees or greater and ISC retracting for 30 seconds.

PCM turns on SERVICE ENGINE SOON light.

Note. Test numbers refer to numbers on diagnostic chart.

1. This step checks for ISC motor codes that can cause other problems.
2. This step checks if cruise control is engaged, causing idle problems.
3. Checks for proper ISC motor operation.
4. Many engine fuel and emissions system faults may cause unstable idle. If base engine idle is not steady, ISC may not be able to control idle to within 152 RPM of desired idle. For symptom diagnosis, see TESTS W/O CODES article in this section.
5. This step checks PCM's ability to control ISC motor by checking for signal present at ISC motor.
6. This step checks for open or short to ground in circuit No. 425 or 426.
7. Checks PCM's ability to control ISC motor by checking for signal present at ISC motor.
8. Checks if ISC motor is receiving signal but not responding correctly. Voltage should fluctuate continuously from negative to positive value.

Scheme 98

Scheme 99

PCM CODE P031 - SHORTED MAP SENSOR CIRCUIT

MAP sensor output signal voltage is a DC voltage varying with manifold pressure. PCM provides a 5-volt reference signal and ground. MAP signal varies between zero and 5 volts as manifold pressure changes. As MAP decreases, voltage decreases (low engine load, high vacuum). As MAP increases, voltage increases (high engine load, low vacuum).

PCM uses MAP sensor values to indicate engine load. A high MAP reading indicates heavy load and low MAP indicates low load. PCM Code P031 is designed to set when PCM detects a MAP sensor signal out of high limits.

Tested continuously.

MAP value high for at least .25 second.

PCM turns on SERVICE ENGINE SOON light, sets BARO equal to 92 kPa and uses a substitute MAP sensor value based on engine RPM and throttle switch status (open or closed). PCM disables long term fuel trim.

Note. Test numbers refer to numbers on diagnostic chart.

1. If PCM parameter PD02 goes to 14-106 kPa with sensor unplugged, fault is at MAP sensor or sensor connector.
2. This checks for an open circuit from terminal "A" of sensor connector to PCM terminal 2A5 (ground). If ground is open, sensor cannot divide reference voltage to make signal voltage vary. Signal voltage is always high.

Manipulate affected wiring and connectors while observing PCM parameter PD02. Apply and release vacuum to MAP sensor vacuum port using a vacuum source. If PCM parameter PD02 displays greater than 108 kPa, condition has been induced and intermittent should be repaired. If wiring and connectors are okay, substitute a known good sensor, and retest.

Scheme 100

PCM CODE P032 - OPEN MAP SENSOR CIRCUIT

MAP sensor changes resistance based upon manifold vacuum. PCM provides a 5-volt reference and ground. MAP signal varies between zero and 5 volts as manifold vacuum varies. PCM Code P032 sets when PCM detects MAP sensor signal is too low.

Test Conditions (1)

Engine speed less than or equal to 700 RPM, throttle angle less than or equal to 18 degrees and TP sensor closed.

Test Conditions (2)

Engine speed less than or equal to 1800 RPM, throttle angle less than or equal to 18 degrees, TP sensor open and transmission not in Park or Neutral.

MAP value less than 15 kPa for .2 second.

PCM turns on SERVICE ENGINE SOON light. PCM sets BARO to 92 kPa. PCM uses a substitute MAP value based on engine RPM and throttle switch status (open or closed). PCM disables long term fuel trim.

Note. Test numbers refer to numbers on diagnostic chart.

1. This checks PCM's ability to respond to a 5-volt signal on MAP input. A reading of 106-109 kPa means wiring and PCM are okay.
2. This checks for 5-volt reference signal at sensor connector.
3. This checks circuit No. 432 for short to ground.
4. This checks PCM's ability to respond to a 5-volt signal voltage on MAP input.
5. Fault is most likely at PCM connector. If PCM connector is okay, replace PCM.

PCM Code P032 can be set by an open 5-volt reference signal between PCM and sensor, an open MAP signal between sensor and PCM or a defective MAP sensor. Manipulate affected wiring and connectors while observing PCM parameter PD02. Apply and release vacuum to MAP sensor vacuum port using a vacuum source. If PCM parameter PD02 displays less than 15 kPa, condition has been induced and cause of intermittent can be repaired. If wiring and connectors are okay, substitute a known good sensor, and retest.

Scheme 101

Scheme 102

Scheme 103

PCM CODE P034 - MAP SENSOR SIGNAL TOO HIGH

This test monitors MAP sensor signals for loss of engine vacuum under closed throttle condition. If difference between MAP signal and calculated BARO is 11 kPa or less for 15 seconds, Code P034 sets.

PCM Codes P021, P022, P026, P027, P031 and P032 not set, throttle switch closed, engine speed greater than or equal to 400 RPM, throttle angle less than or equal to 18 degrees and BARO at least 75 kPa.

Difference between MAP and calculated BARO sensor value 11 kPa or less for 15 seconds.

PCM turns on SERVICE ENGINE SOON light. PCM uses a substitute MAP sensor value based on engine RPM and throttle position switch status. PCM disables long term fuel trim.

Note. Test numbers refer to numbers on diagnostic chart.

1. MAP at idle should be 30-50 kPa, depending on engine load. BARO pressure should be 85-105 kPa, depending upon altitude.
2. Check for vacuum at fuel pressure regulator hose. At idle, typical vacuum reading should be 14-20 in. Hg, depending on engine load.
3. Checks for faulty MAP sensor vacuum supply or MAP sensor circuitry.
4. Checks for open sensor ground from sensor to PCM.
5. Checks for short to voltage on sensor signal circuit No. 432.
6. Fault is at PCM connector or PCM. Check for damaged PCM terminals before replacing PCM.

PCM Code P034 is usually set by a vacuum supply problem to MAP sensor. Check for improper vacuum routing, MAP hose not connected to proper throttle body port or MAP hose chafed, pinched or cut. Apply vacuum to MAP hose at throttle body, and look for vacuum leaks in MAP hose or MAP sensor.

Scheme 104

Scheme 105

Scheme 106

Scheme 107

Scheme 108

PCM CODE P037 - SHORTED INTAKE AIR TEMP (IAT) SENSOR SIGNAL

IAT sensor is a thermistor that varies its resistance with temperature. As sensor temperature increases, resistance decreases. High temperature will result in low signal voltage. PCM Code P037 sets when PCM sees an IAT sensor reading of 298°F (148°C) when coolant temperature is less than 212°F (100°C).

PCM Codes P014 and P015 not set. Coolant sensor temperature less than or equal to 212°F (100°C).

IAT sensor value greater than or equal to 298°F (148°C).

PCM turns on SERVICE ENGINE SOON light. PCM substitutes 104°F (40°C) for IAT when coolant temperature is greater than or equal to 104°F (40°C). PCM substitutes coolant temperature for IAT when coolant temperature is less than or equal to 104°F (40°C).

Note. Test numbers refer to numbers on diagnostic chart.

1. With a shorted IAT sensor, PCM parameter PD05 should indicate 148°C or greater. If PD05 does not indicate 148°C or greater, sensor is not shorted. See NOTE ON INTERMITTENTS.
2. Checks for sensor short or circuit No. 472 shorted to ground. If PCM parameter PDO5 stays at 142-151°C with sensor unplugged, circuit is shorted to ground.
3. IAT sensors can be damaged by a backfire in intake. If vehicle has had more than one IAT sensor replaced, check for signs of backfire and high intake manifold temperatures due to improper valve train operation.
4. Fault is most likely at PCM connector or PCM. Check for damaged PCM terminals or poor connection before replacing PCM.

Manipulate circuit No. 472 wiring, IAT sensor and PCM connector while observing PCM parameter PD05. If failure is induced, manifold air temperature will jump from its normal value to shorted reading of 142-151°C. If wiring and connectors are okay, substitute a known good sensor, and retest.

Scheme 109

PCM CODE P038 - OPEN INTAKE AIR TEMP (IAT) SENSOR SIGNAL

IAT sensor is a thermistor that varies its resistance based on temperature. As temperature of sensor decreases, sensor resistance increases. PCM Code P038 sets when PCM sees low voltage signal when coolant sensor temperature is 23°F (-5°C) or greater.

PCM Codes P014 and P015 not set and coolant sensor temperature greater than or equal to 23°F (-5°C).

IAT sensor value less than 35°F (2°C).

PCM turns on SERVICE ENGINE SOON light. PCM uses 104°F (40°C) for a IAT value when coolant temperature is greater than 104°F (40°C). PCM substitutes coolant temperature for IAT when coolant temperature is less than 104°F (40°C).

Note. Test numbers refer to numbers on diagnostic chart.

1. If sensor is open, PCM parameter PD05 should indicate -35°C or less. If PD05 does not indicate -35° or less, sensor signal is not open at this time. See NOTE ON INTERMITTENTS.
2. Checks PCM and sensor circuitry from PCM to sensor connector. If PCM parameter PD05 indicates 148-151°C with connector terminal "A" shorted to terminal "B", sensor circuits and PCM are okay.
3. Checks for open sensor ground.
4. Checks PCM's ability to recognize short to ground on IAT input.
5. Fault is most likely at PCM connector or PCM. Check for damaged PCM terminals or poor connection before replacing PCM.
6. IAT sensor can be damaged by backfire in intake or by excessive intake heat due to valve train faults. If vehicle has had multiple IAT sensor replacements, check for signs of backfire or high intake manifold air temperature due to improper valve train operation.

Manipulate circuits No. 472 and 476 wiring, IAT connector and PCM connector while observing PCM parameter PD05. If failure is induced, IAT will jump from its normal value to open signal circuit reading of -35°C to -40°C. If wiring and connectors are okay, substitute a known good sensor, and retest.

Scheme 110

PCM CODE P039 - TCC ENGAGEMENT PROBLEM (1 OF 5)

This code test monitors engine RPM and vehicle speed and compares them. PCM will set code when engine speed exceeds fault value for a particular vehicle speed. This code can set due to an electrical problem or slippage of Torque Converter Clutch (TCC) or transaxle clutches. If a TCC failure has occurred, failure is more likely to be observed under high road load (high MAP) conditions. Use code snapshot data to confirm failure.

PCM Codes P026, P027, P031, P032 and P034 not set, transaxle in 4th gear and brake off. Engine speed 3100 RPM or less, system in closed loop, MAP 29-80 kPa. TCC commanded on and TCC module solenoid at 100 percent duty cycle. Throttle position switch open.

If engine RPM exceeds RPM for speed listed in TCC APPLIED TEST table for 5 seconds, PCM Code P039 will set.

PCM turns on SERVICE ENGINE SOON light, which remains on for ignition cycle. TCC is disabled for ignition cycle.

Note. Test number refers to number on diagnostic chart.

1. Flow chart will test resistance of TCC solenoid and wiring inside transmission. Road test checks for proper transmission operation. Refer to TCC APPLIED TEST table.

TCC APPLIED TEST (1)

Scheme 111

Scheme 112

PCM CODE P039 - TCC ENGAGEMENT PROBLEM (2 OF 5)

Note. Test numbers refer to numbers on diagnostic chart.

1. Checks for TCC brake switch or wiring fault. Refer to PCM VOLTAGE CHART table. PCM input P171 should cycle from HI or LO to HI if a problem is present. If P171 does not cycle and Transaxle Breakout Box (J-38791) LED indicator is off, check breakout box for proper connection.
2. To adjust brake switch, first fully seat switch in its retainer, then pull up on brake pedal.

PCM VOLTAGE CHART

Scheme 113

PCM CODE P039 - TCC ENGAGEMENT PROBLEM (3 OF 5)

Note. Test number refers to number on diagnostic chart.

1. This checks for a TCC MOD and TCC apply solenoid or wiring fault. Refer to PCM VOLTAGE CHART table.

PCM VOLTAGE CHART

Scheme 114

PCM CODE P039 - TCC ENGAGEMENT PROBLEM (4 OF 5)

Note. Test number refers to number on diagnostic chart.

1. This test checks for shift solenoids "A" and "B" or wiring fault. Refer to PCM VOLTAGE CHART table.

PCM VOLTAGE CHART

Scheme 115

PCM CODE P039 - TCC ENGAGEMENT PROBLEM (5 OF 5)

Note. Test numbers refer to numbers on diagnostic chart.

1. This stall test checks for TCC apply.
2. This test checks for TCC MOD operation.
3. Code set with normal TCC operation may indicate possible transaxle clutch slippage, usually during high road load (high MAP) conditions. Confirm using code snapshot data. Check transaxle for 4th gear clutch slippage.

Note On "No TCC Apply"

This condition is mechanical or hydraulic and could be caused by any of following components, TCC apply solenoid and/or "O" ring, TCC apply value, TCC solenoid screen, turbine shaft and/or seals, or torque converter.

Note On "TCC Applies W/Maximum Pressure, Harsh Apply"

This condition is mechanical or hydraulic and could be caused by following components: TCC MOD solenoid and/or "O" ring or converter clutch regulator valve.

Scheme 116

PCM CODE P040 - OPEN PSPS CIRCUIT

This code test monitors power steering pressure switch. When a load is placed on power steering, such as full lock, switch opens. PCM Code P040 sets when vehicle speed is greater than 45 MPH and pressure switch is open.

Engine running. Vehicle speed greater than or equal to 45 MPH.

Power steering switch open for 15 seconds.

PCM turns on SERVICE ENGINE SOON light.

Manipulate power steering pressure switch connector with engine running. If intermittent is created, code will set. Disconnect and reconnect power steering connector to ensure it is properly latched.

Scheme 117

Scheme 118

PCM CODE P041 - NO CAM SENSOR SIGNAL

Camshaft position sensor is located inside distributor and provides one pulse per rotation of distributor. PCM uses cam sensor signal to determine location of camshaft for proper fuel distribution. PCM Code P041 sets when PCM is receiving reference pulses and does not detect any cam sensor pulses.

PCM Code P012 not set, distributor reference pulses being received and RPM 1600 or less.

PCM receives no camshaft sensor pulses for 5 seconds.

PCM turns on SERVICE ENGINE SOON light.

With engine running, manipulate related connectors and wiring. If intermittent is created, code will set. Disconnect and reconnect distributor connector to ensure it is properly latched.

Scheme 119

Scheme 120

PCM CODE P042 - FRONT OXYGEN SENSOR LEAN SIGNAL

PCM provides a .45-volt reference signal to oxygen sensor on circuit No. 1589. When oxygen sensor temperature is less than 392°F (200°C), sensor signal voltage will be about .45 volt and PCM will keep system in open loop operation. When oxygen sensor temperature is greater than 392°F (200°C), sensor will begin to generate a signal voltage. In a rich environment, signal voltage will be greater than .45 volt. In a lean environment, signal voltage will be less than .45 volt. If PCM is in good control of air/fuel mixture, mixture will change from rich to lean rapidly (at least one change every 2 seconds).

When PCM sees oxygen sensor is generating a signal voltage (greater than .45 volt), PCM will send system into closed loop operation. In closed loop operation, PCM will adjust fuel delivery rate to engine based on oxygen sensor readings.

Code P042 sets if oxygen sensor stays at lean voltage more than 50 seconds during test conditions. Code P042 also sets when an oxygen sensor circuit fault giving a false lean indication exists or when air/fuel ratio is actually lean due to a vacuum leak or fuel control system fault.

PCM Codes P014, P015, P016, P021, P022, P026, P027, P031, P032 and P034 not set. Throttle switch open, throttle angle 5-30 degrees, coolant temperature 180-268°F (82-131°C), oxygen sensor ready (closed loop), RPM at least 800 and MAP at least 21 kPa. Canister purge occurred at full duty cycle for 2 minutes since engine was running and throttle angle 10 degrees or greater. Long term fuel trim not in effect.

Oxygen sensor status stays lean more than 50 seconds.

PCM turns on SERVICE ENGINE SOON light. PCM turns on canister purge solenoid if Code P044 is also set.

Note. Test numbers refer to numbers on diagnostic chart.

1. If PCM Code P017 is present, diagnose this code first since an oxygen sensor not ready can cause other emission related problems.
2. If oxygen sensor is operating correctly, voltage should fluctuate at greater than 0.3 volt. A lean sensor condition will cause voltage to remain at less than 0.3 volt.
3. If voltage measured is greater than 0.15 volt, PCM and circuit No. 1589 are okay. See POWERTRAIN CHARTS for reference to CHART 8.

Scheme 121

PCM CODE P043 - FRONT OXYGEN SENSOR RICH SIGNAL

PCM provides a .45-volt reference signal to oxygen sensor on circuit No. 1589. When oxygen sensor temperature is less than 392°F (200°C), sensor signal voltage will be about .45 volt and PCM will keep system in open loop operation. When oxygen sensor temperature is greater than 392°F (200°C), sensor will begin to generate a signal voltage. In a rich environment, signal voltage will be greater than .45 volt. In a lean environment, signal voltage will be less than .45 volt. If PCM is in good control of air/fuel mixture, mixture will change from rich to lean rapidly (at least one change every 2 seconds).

When PCM sees oxygen sensor is generating a signal voltage (greater than .45 volt), it will send system into closed loop operation. In closed loop operation, PCM will adjust fuel delivery rate to engine based on oxygen sensor readings.

Code P043 sets if oxygen sensor stays at rich voltage more than 45 seconds during test conditions. Code P043 also sets when oxygen sensor circuit fails or when air/fuel ratio is actually rich due to fuel control or emissions system fault.

PCM Codes P014, P015, P016, P021, P022, P026, P027, P031, P032 and P034 not set, throttle switch open, throttle angle 5-30 degrees, coolant sensor temperature 180-268°F (82-131°C), sensor ready (closed loop), vehicle not accelerating or decelerating, and engine speed greater than or equal to 800 RPM. Canister purge occurred at full duty cycle for 2 minutes since engine was running and throttle angle at 10 degrees or greater. Long term fuel trim not in effect.

Oxygen sensor stays rich for more than 50 seconds.

PCM turns on SERVICE ENGINE SOON light. PCM turns on canister purge solenoid if Code P045 is also set.

Note. Test numbers refer to numbers on diagnostic chart.

1. If PCM Code P017 is present, diagnose this code first since an oxygen sensor not ready can cause other emission related problems.
2. If oxygen sensor is operating correctly, voltage should fluctuate at less than 0.6 volt. A rich sensor condition will cause voltage to remain at greater than 0.6 volt.
3. If voltage measured is less than one volt, PCM and circuit No. 1589 are okay. See CHART 8 under POWERTRAIN CHARTS.

Scheme 122

PCM CODE P044 - REAR OXYGEN SENSOR LEAN SIGNAL

PCM provides a .45-volt reference signal to oxygen sensor on circuit No. 412. When oxygen sensor temperature is less than 392°F (200°C), sensor signal voltage will be about .45 volt and PCM will keep system in open loop operation. When oxygen sensor temperature is greater than 392°F (200°C), sensor will begin to generate a signal voltage. In a rich environment, signal voltage will be greater than .45 volt. In a lean environment, signal voltage will be less than .45 volt. If PCM is in good control of air/fuel mixture, mixture will change from rich to lean rapidly (at least one change every 2 seconds).

PCM Code P044 sets if oxygen sensor stays at lean voltage for more than 50 seconds during test conditions. PCM Code P044 also sets when oxygen sensor circuit fails or when air/fuel ratio is actually lean due to vacuum leak or fuel control system fault.

PCM Codes P014, P015, P016, P021, P022, P026, P027, P031, P032 and P034 not set. Throttle switch open, throttle angle 5-30 degrees, coolant sensor temperature 180-268°F (82-131°C), sensor ready (closed loop), RPM greater than or equal to 800 and MAP at 20 kPa or greater. Canister purge occurred at full duty cycle for 2 minutes since engine was running and throttle angle 10 degrees or greater. Long term fuel trim not in effect.

Oxygen sensor status stays lean more than 50 seconds.

PCM turns on SERVICE ENGINE SOON light. PCM turns on canister purge solenoid if Code P042 is also set.

Note. Test numbers refer to numbers on diagnostic chart.

1. If PCM Code P013 is present, diagnose this code first since an oxygen sensor not ready can cause other emission related problems.
2. If oxygen sensor is operating correctly, voltage should fluctuate at greater than 0.3 volt. A lean sensor condition will cause voltage to remain at less than 0.3 volt.
3. If voltage measured is greater than 0.15 volt, PCM and circuit No. 412 are okay. See CHART 7 under POWERTRAIN CHARTS.

Scheme 123

PCM CODE P045 - REAR OXYGEN SENSOR RICH SIGNAL

PCM provides a .45-volt reference signal to oxygen sensor on circuit No. 412. When oxygen sensor temperature is less than 392°F (200°C), sensor signal voltage will be about .45 volt and PCM will keep system in open loop operation. When oxygen sensor temperature is greater than 392°F (200°C), sensor will swing from rich to lean rapidly, at least one swing every 2 seconds, if PCM is in good control of air/fuel mixture.

Code P045 sets when sensor stays at a rich voltage for more than 50 seconds during the test conditions. Code P045 will also set when oxygen sensor circuit fails or when air/fuel ratio is actually rich due to fuel control or emissions system fault.

PCM Codes P014, P015, P016, P021, P022, P026, P027, P031, P032 and P034 not set. Throttle switch open, throttle angle 5-30 degrees, coolant temperature 180-268°F (82-131°C), oxygen sensor ready (closed loop), and engine speed at least 800 RPM. Canister purge occurred at full duty cycle for 2 minutes since engine was running and throttle angle at 10 degrees or greater. Long term fuel trim not in effect.

Oxygen sensor stays rich for more than 50 seconds.

PCM turns on SERVICE ENGINE SOON light. PCM turns on canister purge solenoid if Code P043 is also set.

Note. Test numbers refer to numbers on diagnostic chart.

1. If PCM Code P013 is present, diagnose this code first since an oxygen sensor not ready can cause other emission related problems.
2. If oxygen sensor is operating correctly, voltage should fluctuate at less than 0.6 volt. A rich sensor condition will cause voltage to remain at greater than 0.6 volt.
3. If voltage measured is less than one volt, PCM and circuit No. 412 are okay. See CHART 7 under POWERTRAIN CHARTS.

Scheme 124

PCM CODE P046 - FRONT-TO-REAR BANK FUELING IMBALANCE

PCM controls rear bank fueling based upon rear oxygen sensor and front bank fueling based upon front oxygen sensor. Likely causes for imbalance include lean or faulty injectors on one side of engine, cracked or fouled spark plugs, or exhaust or intake manifold leaks.

Tested continuously.

Front bank block learn values differ from rear bank block learn values by more than 15 counts for 10 minutes.

PCM turns on SERVICE ENGINE SOON light.

Note. Test numbers refer to numbers on diagnostic chart.

1. If any other codes are present, diagnose them first because they can cause a fueling imbalance.
2. This test checks for a physical or mechanical problem causing PCM Code P046 to set.
3. Injector bank that is farthest from neutral value of 128 is bank which is out of fuel. Refer to PCM DATA PARAMETER. (Scheme 37) See appropriate chart under POWERTRAIN CHARTS.

Scheme 125

Scheme 126

Description

PCM and IPC share information through Universal Asynchronous Receiver Transmitter (UART). IPC is master link and data are only transmitted at IPC request. Data are sent in 8-character blocks at a rate of 8192 characters per second.

Data from PCM to IPC contain engine operating information. PCM-IPC data include CTS, RPM and injector pulse width values so IPC can control cooling fans, display RPM and calculate MPG for display at Driver Information Center (DIC) panel. IPC sends PCM air conditioning status to be used for idle speed control and ambient temperature for use in TCC application and release decisions.

PCM Code P047 is set in PCM in event of a UART failure. If fault is a current failure, PCM will not be able to communicate with IPC and PCM Code IO34 will be displayed as current. PCM Code P047 is current in PCM but cannot be sent (displayed) to IPC because of UART fault. If UART fault is corrected, both PCM Code P047 and IO34 will be displayed as history codes.

PCM Code P047 should be diagnosed using chart for IPC Code IO34. Refer to appropriate INSTRUMENT PANEL article in the ACCESSORIES/SAFETY EQUIPMENT Section.

PCM Code P047 stored as history can indicate 2 failures

1. Open in circuit No. 800. Symptoms will be: A - SYSTEM FAULT message on DIC panel. B - SERVICE ENGINE SOON and CHECK INFO CENTER lights on. C - Diagnostics entered; NO PCM DATA displayed on DIC panel. D - When fault is repaired, PCM Codes P047 and IO34 show as history codes.
2. Grounded circuit No. 800 at any point. Symptoms will be: A - SYSTEM FAULT message on DIC panel. B - SERVICE ENGINE SOON light on. C - Instrument panel gauges flash. D - Climate control panel goes blank. E - Engine cooling fans go on high speed. E - Diagnostics disabled; SYSTEM FAULT message stays on DIC panel. F - When fault is repaired, diagnostics show PCM Codes P047, IO33, IO34 and IO37 as history codes.

PCM Code P012 not set, ignition on and engine speed greater than 500 RPM for 20 seconds.

PCM receives invalid data from IPC for 5 seconds.

PCM turns on SERVICE ENGINE SOON light, clears all IPC data from PCM memory and disables A/C clutch. Cooling fan control will be based on engine coolant temperature only.

PCM CODE P048 - EGR SYSTEM FAULT

To perform test, PCM turns off EGR flow to engine and monitors oxygen sensor (closed loop) integrator. With EGR off, integrator should swing to a greater value, reflecting leaner air/fuel mixtures. If integrator does not swing to a greater value, PCM assumes either EGR was turned off before test started or EGR is flowing and PCM does not have ability to turn it off. PCM monitors EGR 5 times in a given key cycle. If EGR does not respond 3 or more times during a key cycle, PCM Code P048 is set.

EGR failed in entire ignition cycle. PCM Codes P013, P014, P015, P017, P021, P022, P031, P032, P034, P042, P043, P044 and P045 not set. Coolant temperature 176-230°F (80-110°C), throttle angle 7-14 degrees, RPM 1450-1650 and oxygen sensor in closed loop operation at greater than 35 MPH, 10-minute timer after start-up expired and throttle steady. MAP between 40-75 kPa.

PCM turns off EGR system for 5 seconds. PCM monitors rear fuel integrator for change. Oxygen sensor fails to indicate a leaner mixture in at least 3 of 5 tests during key cycle.

PCM turns on SERVICE ENGINE SOON light for entire key cycle and EGR is disabled for entire key cycle.

Note. Test numbers refer to numbers on diagnostic chart.

1. Checks for EGR operation using PCM override.
2. Checking EGR gases entering intake manifold by raising EGR valve off of its seat.
3. Checking EGR solenoid ability to pass vacuum.
4. With engine at idle, EGR solenoid should be energized. Test light across EGR solenoid terminals should be illuminated.
5. Checks PCM's ability to turn off EGR solenoid.

With engine at idle, manipulate EGR solenoid connector and related wiring. Listen for a change in idle quality. Drive vehicle with throttle angle at 8-15 degrees and engine at 1450-1650 RPM to try to duplicate code. Remove EGR valve, and check it for carbon build-up which would restrict EGR flow and for foreign materials holding EGR valve open. Check for pinched, cut, kinked, misrouted or blocked vacuum passages and/or vacuum hoses reducing EGR flow. Check for EGR valve binding in up or down position.

Scheme 127

Scheme 128

PCM CODE P051 - PROM ERROR

Ensure PROM is fully inserted in socket. If PROM is fully inserted, replace PROM, clear memory and recheck. If PCM Code P051 reappears, replace PCM.

See cautions under ELECTRONIC CONTROL MODULE (ECM) in I - SYS/COMP TESTS article in this section when replacing PROM or PCM.

PCM CODE P052 - PCM MEMORY RESET

This code test monitors PCM long term memory for a loss or unintended change of data. If battery power or ground is disconnected, PCM Code P052 will set, and should be cleared when battery power is restored. PCM keeps a running check on memory. If memory changes, Code P052 resets. If P052 is accompanied by driveability symptoms and/or other stored codes. Check for intermittent loss of power or ground to PCM, and inspect PCM connectors.

Tested continuously.

Loss of primary battery power and data to PCM.

PCM Code P052 is set. SERVICE ENGINE SOON light is not illuminated.

PCM CODE P053 - DISTRIBUTOR SIGNAL INTERRUPT

PCM Code P053 is set if PCM does not receive distributor reference pulses from Ignition Control Module (ICM) for more than .4 second. Since PFI system requires ICM pulses in order to trigger injectors, most occurrences of PCM Code P053 will be accompanied by a stall.

PCM Code P019 not set and engine speed greater than 568 RPM.

No distributor reference pulses received by PCM for .4 second.

PCM Code P053 is set. SERVICE ENGINE SOON light is not illuminated.

Note. Test number refers to number on diagnostic chart.

1. A set of jumper wires is required on these tests.

DO NOT attempt to diagnose PCM Code P053 unless complaints of stumble, stall, miss or other driveability conditions which could be caused by loss of spark or fuel exist. PCM Code P053 can be caused by loss of ground on circuit No. 453, loss of distributor reference signal on circuit No. 430, loss of battery power to "B+" terminal of distributor or faulty ignition switch circuit.

Scheme 129

PCM CODE P055 - TP SENSOR OUT OF RANGE

TP sensor is self-adjusting. With ignition off, PCM executes a TP sensor learning routine. After ignition is turned off, PCM will retract ISC until ISC throttle switch opens and throttle linkage is resting on minimum air screw. PCM then stores TP sensor value and calculates a correction.

If same correction factor occurs on 2 consecutive key off cycles, TP sensor is corrected to zero degrees using correction factor learned. If value needs correction by more than -2.9 degrees or +3.0 degrees, PCM Code P055 will be stored in memory at next key on cycle. Parameter PD01 displays incorrect TP sensor values.

Tested continuously.

"Learned" TP sensor is less than -2.9 degrees or greater than 3 degrees.

At next key on, PCM will log PCM Code P055 as current. No diagnostic light or service message will appear.

Note. Test numbers refer to numbers on diagnostic chart.

1. Checks for TP sensor adjustment. PCM parameter PD01 displays incorrect TP sensor so it can be used to check TP sensor adjustment.
2. TP sensor adjustment is okay.
3. If TP sensor adjustment is okay, ISC and throttle switch operation need to be thoroughly checked. Throttle linkage needs to be checked for proper operation. Check throttle and cruise cables, ensure throttle valves are not binding, check for proper throttle return spring operation and ensure throttle shaft and blades move freely.

Manipulate ISC wiring while observing PCM input PI72 and while observing ISC operation during PCM output PO07. Manipulate TP sensor wiring and connector while observing PCM parameter PD01 for jumps, skips and/or intermittent behavior.

Ensure TP sensor is secured to throttle body (both screws tight). Cycle TP sensor through its full travel while observing parameter PD01 for erratic behavior. Check for proper TP sensor part number installed on vehicle. Unplug and reconnect TP sensor, ISC and PCM connectors, and ensure they are latched properly.

Scheme 130

PCM CODE P056 - TRANSAXLE INPUT SPEED SENSOR CIRCUIT PROBLEM

This test checks transaxle input speed sensor circuit problem. If engine is running and vehicle is moving at greater than 10 MPH, then transaxle input speed must be non-zero. If turbine speed is less than 50 MPH with vehicle speed of 10 MPH or greater, Code P056 will set.

Codes P024, P075 and P091 not set. Transaxle not in Park or Neutral. Vehicle speed at 10 MPH or greater.

Turbine speed 50 rpm or less for 2 seconds.

Note. Test numbers refer to numbers on diagnostic chart.

1. With engine idling in Park or Neutral, PCM data PD72 should read 50-100 RPM less than engine RPM.
2. Transaxle input speed sensor should generate a frequency of greater than zero Hertz with engine at idle. If frequency is not as specified, check circuits No. 1230 and 1231 and speed sensor for open or short inside transaxle.
3. Checks circuits No. 1230 and 1231 for open or short to PCM. If circuit is okay, PCM is faulty.

Manipulate circuits No. 1230 and 1231. Look for EMI sources, such as sensor wires running along spark plug cables or high power transmitters in vicinity.

Scheme 131

Scheme 132

CODE P057, SHORTED TRANSAXLE TEMPERATURE SENSOR CIRCUIT

Transaxle temperature sensor resistance decreases as sensor temperature increases. A high transaxle temperature will result in low signal voltage on circuit No. 585 (Tan/White wire). Code P057 sets when PCM sees a transaxle temperature reading of 298°F (148°C) or greater (.08 volt or less).

Test continuously.

Transaxle temperature sensor value at 298°F (148°C) or greater for 5 seconds.

PCM turns on SERVICE VEHICLE SOON message. PCM substitutes engine coolant temperature value for transaxle temperature until engine coolant temperature reaches 221°F (105°C) before it sets to hot mode operation. Transaxle shift adapts and garage shift adapts are maintained in current levels.

Note. Test numbers refer to numbers on diagnostic chart.

1. If transaxle temperature sensor is shorted, PCM data parameter PD77 should read 298°F (148°C) or greater. If parameter does not show this reading, sensor and wiring are okay.
2. Checks if circuit No. 585 (Tan/White wire) is shorted. If parameter value stays at -18°F (-28°C) or greater with transaxle temperature sensor connector disconnected, check for short between sensor connector and PCM terminal No. 1B14.
3. Checks for short to ground on circuit No. 585 (Tan/White wire) inside transaxle. If wire is okay, replace shorted transaxle temperature sensor.

Scheme 133

Scheme 134

Scheme 135

PCM CODE P058 - PASS-KEY FUEL ENABLE PROBLEM

PASS-Key system enables engine operation by allowing starter to engage and issuing a fuel enable signal to PCM. Once engine is running, PCM constantly monitors fuel enable signal from PASS-Key module. PCM will not cancel fuel injection once it has seen a proper PASS-Key module signal; therefore, stalling conditions cannot occur as a result of a PASS-Key malfunction.

Engine has been running for a predetermined amount of time. PASS-Key engine start timer expired.

PASS-Key fuel enable input incorrect but has been correct within this engine run cycle.

THEFT SYSTEM PROBLEM, CAR MAY NOT RESTART message is displayed on DIC. Enables fuel injection on future ignition cycles without regard for PASS-Key fuel enable input status.

Note. Test numbers refer to numbers on diagnostic chart.

1. If engine will crank, problem has been isolated to PASS-Key module, PCM or fuel enable circuit. If engine will not crank, perform PASS-Key system diagnosis. See PASS-KEY DIAGNOSIS.
2. Checking voltage to PCM will identify if PCM is at fault. Typical signal will be about 2.5 volts.
3. Voltage too low; problem could be a faulty PASS-Key module, poor connection at PCM or a short to ground in fuel enable circuit.
4. Voltage too high; problem could be a faulty PASS-Key module, poor connection at PASS-Key module, short to voltage or an open in fuel enable circuit.

If code is intermittent, check for short to ground or voltage on circuit No. 229, intermittent open in circuit No. 229 or intermittent loss of power to module.

PASS-Key Diagnosis

PASS-Key system interfaces PCM and starter with a power source, decoder module, starter enable relay, ignition switch and instrument cluster. Before replacing PASS-Key module, check system for following common problems.

1. Check ignition key pellet sensing contacts in ignition lock cylinder. Look into cylinder lock. If contacts are damaged, replace cylinder lock.
2. Check PASS-Key, PCM and GAGES fuses.
3. Check SECURITY indicator bulb in instrument panel.
4. A defective resistor pellet within ignition key or incorrect resistance value of key (15 different assigned values) will cause vehicle not to start. Key must be correct electrically and mechanically.

If incorrect key is used to try to start vehicle, decoder will not allow vehicle to start for 2-4 minutes, even if after correct key is inserted.

Scheme 136

PCM CODE P060 - CRUISE CONTROL WITH TRANSAXLE NOT IN DRIVE

PCM Code P060 sets if cruise control is engaged and park/neutral switch is closed, indicating transaxle is in Park or Neutral.

Cruise control on and engaged.

Transaxle in Park or Neutral.

PCM disengages cruise control.

If PCM Code P060 is stored as a history code, select PCM data PD71 and PD72. Manipulate harness while observing status of switch. If switch changes status as wiring is manipulated, repair intermittent connections. If no trouble code is found, code may have been set if transmission was inadvertently put into Neutral while cruise control was engaged.

Scheme 137

PCM CODE P061 - CRUISE CONTROL VENT SOLENOID PROBLEM

PCM Code P061 will set if PCM output PO07 is commanding vent solenoid off and feedback is indicating that it is on or PCM is commanding vent solenoid on and feedback is indicating that it is off for 0.5 second.

Tested continuously.

Cruise vent solenoid commanded off but feedback indicates solenoid is on or cruise vent solenoid commanded on but feedback indicates solenoid is off.

PCM disables cruise control.

Note. Test numbers refer to numbers on diagnostic chart.

1. Checks to see if fault is due to cruise control servo or circuit. Frequency should cycle between zero and a non-zero number. If DVOM stays at zero, circuit or PCM is at fault.
2. Checks for short to voltage in circuit No. 403.
3. Checks for open in circuit No. 450.
4. Checks PCM's ability to control cruise control servo. Voltage should cycle between zero and 12 volts. If voltage does not cycle, check for open in circuit No. 403.

If intermittent PCM Code P061 is being set, slowly manipulate wiring while in output function PO07. Listen for solenoid to cycle on or off. PO07 cycles solenoid on and off every 3 seconds.

Scheme 138

Scheme 139

PCM CODE P062 - CRUISE CONTROL VACUUM SOLENOID PROBLEM

PCM Code P062 will set if PCM output PO08 is commanding vacuum solenoid off and feedback is indicating that it is on, or PCM is commanding vacuum solenoid on and feedback is indicating that it is off for 0.5 second.

Tested continuously.

Cruise vacuum solenoid commanded off but feedback indicates solenoid is on, or cruise vacuum solenoid commanded on but feedback indicates solenoid is off.

PCM disables cruise control.

Note. Test numbers refer to numbers on diagnostic chart.

1. Checks if fault is due to cruise control servo or circuit. Frequency should cycle between zero and a non-zero number. If DVOM stays at zero, circuit or PCM is at fault.
2. Checks for short to voltage in circuit No. 402.
3. Checks for open in circuit No. 450.
4. Checks PCM's ability to control cruise control servo. Voltage should cycle between zero and 12 volts. If voltage does not cycle, check circuit No. 402 for open.

Scheme 140

PCM CODE P063 - VEHICLE SPEED & SET SPEED DIFFERENCE TOO HIGH

Code P063 will set and disengage cruise control if vehicle speed is 20 MPH greater than cruise set speed. PCM Code P063 is designed to detect a cruise control problem that results in cruise overspeed or inability to hold speed.

Tested when cruise control is enabled and engaged, and cruise control servo position is at 39 percent or greater.

Vehicle speed 20 MPH greater than set speed for .5 second.

PCM disengages cruise control.

Scheme 141

PCM CODE P064 - CRUISE CONTROL ENGAGED/ACCELERATION TOO HIGH

PCM Code P064 will set when vehicle speed is increasing at a rapid rate (wheel spin). This protective measure prevents wheel spin on icy roads when cruise control is in operation.

If PCM Code PO75 is also present, check for sources of Electromagnetic Interference (EMI), such as VSS wires run along side spark plug wires or high power transmitters (mobile radios) operating in vicinity.

Cruise is engaged.

Vehicle speed increases more than 16 MPH in one second with cruise control engaged.

PCM disengages cruise control. If Code PO64 is present and no other cruise control faults exists, clear code and road test vehicle.

PCM CODE P065 - CRUISE CONTROL SERVO POSITION SENSOR FAILURE

Cruise servo position sensor is a potentiometer that changes resistance with servo position. PCM Code P065 sets when PCM detects a low voltage, indicating a short to ground in cruise servo position sensor circuit.

Tested continuously.

Cruise control servo position 1.9 percent or less for 0.9 second.

PCM disables cruise control.

Note. Test numbers refer to numbers on diagnostic chart.

1. Checks if cruise control feedback is a value that it should never be, even with servo fully released.
2. Checks PCM and circuit to cruise control servo are okay. Voltage reading should be 4.6-5.1 volts.
3. Checks circuit No. 399 for an open.
4. Checks circuit No. 398 for an open.
5. Checks circuit No. 398 for short to ground. If wire is okay, PCM is open internally.
6. Checks if cruise control servo is operating normally. If feedback is greater than 30, servo is operating correctly.

Scheme 142

PCM CODE P066 - ENGINE RPM TOO HIGH WITH CRUISE ENGAGED

PCM Code P066 will set when engine speed is greater than 4800 RPM with cruise engaged. This may occur on slippery pavement, extended wide open throttle acceleration or for some other mechanical problems (such as transaxle slippage). Under these conditions, PCM Code P066 is normal. Vehicle operator should be advised why cruise control de-energized. Clear code, and road test vehicle to verify normal operation.

Cruise is enabled and engaged. Vehicle operator not manually controlling throttle position.

Engine at 4800 RPM or greater for 0.5 second.

PCM disengages cruise control.

PCM CODE P067 - SET/COAST OR RESUME/ACCEL SWITCH SHORTED

When cruise control is on, system voltage is available at one side of normally open contact of SET/COAST and RESUME/ACCEL switches. If cruise control switch is in ON position, voltage is available to switches when ignition is turned on. If SET/COAST or RESUME/ACCEL switches were stuck on or shorted to power, cruise control operation would begin. To prevent this, PCM Code P067 will set and cruise control operation is disabled if signal voltage from SET/COAST (circuit No. 84) or RESUME/ACCEL (circuit No. 87) is high continuously for 10 minutes. Cruise control will be disengaged until PCM sees a low voltage on both of these signals.

Tested continuously.

SET/COAST and RESUME/ACCEL switches are both closed for 10 minutes.

PCM disengages cruise control.

Note. Test numbers refer to numbers on diagnostic chart.

1. Checks if PCM input data PI83 (SET/COAST) and PI84 (RESUME/ACCEL) will cycle from LO to HI to LO. If inputs remain high, a short to voltage in system is present.
2. Checks if SET/COAST and/or RESUME/ACCEL switches are shorted to voltage.
3. Checks if circuit No. 84 is shorted to voltage.
4. Checks if circuit No. 87 is shorted to voltage.

Scheme 143

PCM CODE P068 - CRUISE CONTROL SERVO POSITION OUT OF RANGE

PCM Code P068 is set and cruise control is disabled when cruise control servo feedback reading is significantly higher or lower than commanded value for a period of time.

Cruise control engaged.

Throttle angle greater than 20 degrees and servo position sensor indicating a stroke of at least 7 percent greater than commanded value for 2 seconds.

PCM disables cruise control for entire ignition cycle.

Note. Test numbers refer to numbers on diagnostic chart.

1. Checks if PCM override PS07 can fully retract cruise control servo.
2. Checks if PCM override PS07 is able to fully relax cruise control servo.
3. Checks to see if problem is due to binding or a short to voltage on circuit No. 403 is keeping cruise control servo from fully relaxing.

Scheme 144

Scheme 145

Scheme 146

PCM CODE P070 - INTERMITTENT TP SENSOR SIGNAL

This test monitors MAP and TP sensors. PCM Code P070 will set if MAP value remains constant and TP sensor value changes considerably. Engine operation requires that any large change in TP sensor value must be followed by a change in MAP sensor value.

PCM Codes P031, P032 and P034 not set. Throttle angle changes more than 3.5 degrees in 12.5 milliseconds (.0125 seconds). Engine not decelerating (MAP drops to 22 kPa or less). Engine not accelerating (MAP is within 7.4 kPa of atmospheric pressure). Engine running.

MAP changes 4 kPa or less in .16 second following change in throttle angle.

None.

Note. Test number refers to number on diagnostic chart. Reference to CHART 3 refers to POWERTRAIN CHARTS.

1. Checking PCM Code P070 snapshot value is used to determine if an intermittent low or high voltage caused code to set. An intermittent low voltage can be caused by an open or short to ground in circuit No. 417, an open in circuit No. 474 or a faulty TP sensor. An intermittent high voltage can be caused by an open in circuit No. 1076 or a short to voltage on circuit No. 417.

Scheme 147

PCM CODE P071 - INTERMITTENT MAP SENSOR SIGNAL

This test monitors TP sensor, RPM, MAP, EGR flow and A/C clutch status. If MAP changes rapidly and all other parameters remain constant, PCM Code P071 will set. Engine operation requires a large change in manifold pressure must be preceded by a change in throttle angle.

PCM Codes P021 and P022 not set. TP sensor does not change more than .8 degree for 1.01 seconds. Engine speed does not change more than 100 RPM for 1.01 seconds. EGR does not change more than 4 percent for 1.01 seconds. A/C clutch not commanded on or off.

MAP sensor reading changes more than 5.5 kPa in 12.5 milliseconds (.0125 second).

PCM uses substitute MAP value based on engine RPM and throttle position switch status.

Note. Test numbers refer to numbers on diagnostic chart. Reference to CHART 3 refers to POWERTRAIN CHARTS.

1. Checks if MAP can read BARO pressure correctly (87-105 kPa).
2. Checks MAP sensor's ability to react to a known vacuum (26-34 kPa).
3. Checks MAP sensor's ability to react to sudden change in vacuum.

Scheme 148

PCM CODE P073 - INTERMITTENT COOLANT TEMP SENSOR SIGNAL

Coolant Temperature Sensor (CTS) circuit uses 2 pull-up resistors for temperature sensing. When sensor resistance is high (indicating low temperatures), PCM uses 3.65-k/ohm resistor and 348-ohm resistor in series. As temperature increases to 122°F (50°C), sensor resistance will decrease to 973 ohms. This resistance corresponds to .97 volt at PCM. At this point PCM shifts to single 348-ohm pull-up resistor to measure temperature greater than 122°F (50°C).

PCM monitors voltage signal of circuit and assumes engine operation causes coolant temperatures to change at slow rates. This test monitors CTS voltage. If PCM detects a large change in sensor output voltage in a one-second period, code will set.

Two seconds have passed since ignition has been turned on and 2 seconds have passed since PCM had shifted CTS pull-up resistors. This occurs when sensor resistance indicates 122°F (50°C).

CTS voltage changes .3 volt in one second.

PCM Code P073 is set. No service message is given.

Note. Test number refers to number on diagnostic chart. Reference to CHART 3 refers to POWERTRAIN CHARTS.

1. Checks PCM Code P073 snapshot value to determine if an intermittent high or low resistance caused code to set. An intermittent high resistance can be caused by an open in circuit No. 410 or 1076. An intermittent low resistance can be caused by a short to ground in circuit No. 410.

Scheme 149

PCM CODE P074 - INTERMITTENT INTAKE AIR TEMP SENSOR SIGNAL

PCM Code P074 will set when PCM detects a large change in sensor output voltage in a .3-second period of time.

Two seconds have passed since ignition switch has been turned to RUN position.

IAT sensor voltage changes .3 volt (11°C) in 250 milliseconds.

None.

Note. Test number refers to number on diagnostic chart. Reference to CHART 3 refers to POWERTRAIN CHARTS.

1. Checks PCM Code P074 snapshot to determine if an intermittent high or low resistance caused code to set. An intermittent high resistance can be caused by an open in circuit No. 476 or 472. An intermittent low resistance can be caused by a short to ground on circuit No. 472.

Scheme 150

PCM CODE P075 - VSS SIGNAL INTERRUPT

This test compares vehicle speed to manifold pressure. Change in MAP must correspond with a change in vehicle speed. PCM will ignore test if conditions for engine idle are present. If vehicle speed changes 8 MPH or greater in one second and is not accompanied by a greater than 2 kPa change in MAP, Code P075 will set.

PCM Codes P031, P032 and P034 not set, engine running (not at idle) and brakes not applied.

Vehicle speed change of 8 MPH or more in a one-second time period with a corresponding MAP change of 2 kPa or less.

No service message is given.

Manipulate VSS wiring and connectors and verify wiring is not too close to spark plug wires. Code can be caused by an open, short to ground, or short to voltage on circuit No. 400 or 401. Also, check for an open or shorted sensor connector, engine-to-dash connector or PCM connector. Check for defective sensor. If wiring and connectors are okay, substitute a known good sensor, and retest.

Scheme 151

Scheme 152

Scheme 153

PCM CODE P080 - FUEL SYSTEM RICH

Purpose of this code test is to detect a rich condition caused by fuel injection system or by evaporative fuel canister purging continuously. Code can be set only during sustained steady driving, such as sustained cruise control operation.

When all conditions have been met and block learn is 104 or less, system turns off canister purge to attempt to lean out system. If block learn is still 104 or less (rich), code is set.

PCM Codes P014, P015, P016, P021, P022, P026, P027, P031, P032 and P034 not set. System in closed loop, throttle switch open, throttle angle 6-30 degrees and coolant temperature greater than 180°F (82°C). Canister has been at a purge duty cycle of 94 percent (purge enabled) at a 5-30 degree throttle angle for 10 minutes. Rear oxygen sensor ready. Long term fuel trim not in effect.

Rear long term fuel trim (block learn) is at 104 or less for 25 seconds.

Code set. PCM turns on SERVICE ENGINE SOON light.

Possible Causes

Rich fuel system condition can be caused by leaking fuel injectors, defective fuel pressure regulator, restricted or blocked fuel return line, leaking purge valve, defective purge solenoid, open or short in purge solenoid circuit or defective powertrain control module. To diagnose fuel system concerns, see BASIC FUEL SYSTEM CHECKS (A-7) in appropriate BASIC DIAGNOSTIC PROCEDURES article. To diagnose purge control system concerns, see EMISSION SYSTEMS & SUB-SYSTEMS in appropriate SYSTEM & COMPONENT TESTING article.

Scheme 154

Scheme 155

Scheme 156

Scheme 157

Scheme 158

Scheme 159

Constantly monitored.

Coast down throttle angle offset greater than 5 degrees from learned value.

PCM will set Code P085 and turn on SERVICE ENGINE SOON light.

Note. Test number refers to number on diagnostic chart.

1. If engine stalls, continue test. Stall may be caused by carbon deposits on throttle valves and in throttle bores.

Scheme 160

Scheme 161

Scheme 162

Scheme 163

Scheme 164

Scheme 165

Scheme 166

Scheme 167

Scheme 168

Scheme 169

PCM Code P024 not set, engine running and vehicle speed greater than 30 MPH.

Vehicle speed cycles from 30 MPH or greater to zero MPH with no TCC brake switch input. PCM must record 10 of these events to set code.

PCM will set Code P090 and turn on SERVICE VEHICLE SOON message. PCM disables cruise control.

Note. Test numbers refer to numbers on diagnostic chart.

1. Tests TCC brake switch input to PCM data parameter PI71. If input is working correctly, display will change from HI to LO to HI. If display remains on HI, check circuit No. 420 and TCC brake switch for short to voltage. If display remains on LO, check circuit No. 420 for an open or short to ground.
2. Checks for voltage present at TCC brake switch connector terminal "A".
3. Checks resistance between TCC brake switch terminal "A" and ground.
4. Checks resistance between TCC brake switch terminal "B" and ground.
5. Checks if TCC brake switch needs to be adjusted or replaced, or if PCM is faulty.

Scheme 170

Constantly monitored.

Any 4-digit code that does not match codes shown in chart for 64 seconds. Engine start while Code 1100 (Park) or Code 1010 (Neutral) not present. PCM commanding 4th gear although engine-to-vehicle speed indicating 4th gear achieved with Code 1100 (Park) or Code 1010 (Neutral).

PCM turns on SERVICE VEHICLE SOON message. PCM disables cruise control.

If all digits of PD71 and PD72 are 1, check for an intermittent loss of ground in park/neutral switch. If an intermittent PCM Code P091 occurs when gear selector lever is moved, code is most likely caused by a misadjusted shift linkage or park/neutral switch, causing park/neutral switch to end up in range between gears.

If code and SERVICE VEHICLE SOON message comes on while driving or when gear selector is not being moved, record PD71 and PD72 and compare values to chart. For example, if transmission was in OD when message came on and PD71 indicates 10 and PD72 indicates 11, check for intermittent open in circuit No. 773.

Manipulate related wiring and connectors while observing parameters PD71 and PD72 (or scan tester display). If an intermittent is induced, digit corresponding to that circuit will change. If wiring and connectors are okay, substitute a known good park/neutral switch, and recheck.

Scheme 171

Scheme 172

PCM CODE P092 - HEATED WINDSHIELD REQUEST PROBLEM

This test will detect a problem with heated windshield fast idle request circuit to PCM. When circuit is grounded by heated windshield module, PCM will increase idle speed to compensate for extra load placed on alternator. Code P092 will set when signal is low for more than 10 minutes.

Engine running.

Heated windshield request present at PCM for more than 10 minutes.

Code set. PCM turns on SERVICE VEHICLE SOON message.

Scheme 173

Scheme 174

Scheme 175

Scheme 176

Scheme 177

Scheme 178

Scheme 179

Scheme 180

Scheme 181

Scheme 182

PCM CODE P096 - TORQUE CONVERTER OVERSTRESS

Primary purpose of PCM Code P096 is to detect an action of driver which could cause an unsafe condition or damage to vehicle. PCM Code P096 can be driver-induced by depressing accelerator and brake at same time. PCM Code P096 will not set if PCM Code P090 or P091 is current.

PCM Codes P021, P022 and P024 not set.

Brake applied, transaxle in Drive or Reverse, vehicle speed 5 MPH or less and throttle angle greater than 65 degrees for 12 seconds.

PCM Code P096 is set. PCM turns on SERVICE ENGINE SOON message.

PCM CODE P097 - PARK/NEUTRAL-TO-DRIVE/REVERSE SHIFT AT HIGH THROTTLE ANGLE

Primary purpose of PCM Code P097 is to detect an action of vehicle operator which could cause an unsafe condition or damage to vehicle. PCM Code P097 can be driver-induced by shifting from Park or Neutral to Drive or Reverse with throttle angle at 20 degrees or greater. Throttle angle must be less than 16 degrees to re-enable fuel injectors after code sets. Check for proper TP sensor operation.

PCM Codes P021 and P022 not set.

Engine speed greater than 2000 RPM, gear selector moved from Park or Neutral to Drive or Reverse, vehicle speed less than 6 MPH and throttle angle is 20 degrees or greater.

PCM will disable selected injectors to reduce engine power and set PCM Code P097. No service message is given.

PCM CODE P098 - PARK/NEUTRAL-TO-DRIVE/REVERSE SHIFT WHILE IN ISC CONTROL RANGE

This test monitors idle speed and gear selection from Park or Neutral to Drive or Reverse when throttle is in ISC speed range. If idle speed is greater than desired, PCM will retard spark advance and set code.

PCM Code P098 could be driver-induced by shifting into gear with throttle angle of less than 20 degrees with throttle depressed.

PCM Codes P021 and P022 not set.

Engine running and gear selector moved from Park or Neutral to Drive or Reverse. Engine speed 600 RPM greater than engine speed determined by PCM. Throttle angle at 20 degrees or less and vehicle speed less than 6 MPH.

PCM will retard ignition timing and set PCM Code P098. No service message is given.

PCM CODE P099 - CRUISE SERVO APPLIED NOT IN CRUISE

This diagnostic test monitors cruise control servo position sensor to ensure servo has released throttle after cruise control has been disengaged for 2 seconds. If cruise control servo has not been released, Code P099 will set and engine power will be reduced by disabling fuel to individual cylinders. Code P068 may disable cruise control and lead to setting Code P099.

Engine running. Code PS07 override not active.

Failure conditions for PCM code set change depending on whether code was previously set or not.

Code P099 not previously set

1. Cruise control disengaged for 2 seconds.
2. Throttle angle greater than 20 degrees, TP sensor not failed.
3. MAP greater than 70 kPa, TP sensor failed.
4. Cruise control servo stroke greater than 63 percent for 0.1 second.

Code P099 previously set

1. Cruise control disengaged for 2 seconds.
2. Throttle angle greater than 16 degrees, TP sensor not failed.
3. MAP greater than 55 kPa, TP sensor failed.
4. Cruise control servo stroke greater than 38 percent for 0.1 second.

PCM disables cruise control and reduces fuel delivery to selected cylinders.

Note. Test numbers refer to numbers on diagnostic chart.

1. Checks if PCM can control cruise control solenoid.
2. Checks if cruise control position sensor is working correctly.
3. Checks if cruise control servo will extend fully. If servo does not extend fully, check circuit No. 402 for a short to voltage.

Scheme 183

Scheme 184

Scheme 185

Scheme 186

Scheme 187

Scheme 188

Scheme 189

Scheme 190

Scheme 191

Scheme 192

Scheme 193

Scheme 194

Scheme 195

Scheme 196

Scheme 197

Scheme 198

Scheme 199

Scheme 200

Scheme 201

Scheme 202

Scheme 203

Scheme 204

Scheme 205

Scheme 206

SUMMARY

If no "current" codes are present, and driveability symptoms exist or "history" codes exist, proceed to TESTS W/O CODES article in this section for diagnosis by symptom (i.e., ROUGH IDLE, NO START, etc.) or intermittent diagnostic procedures.

See also:
• P012
• P013
• P014
• P015
• P016
• P017
• P019
• P020
• P021
• P022
• P023
• P024
• P026
• P027
• P030
• P031
• P032
• P034
• P037
• P038
• P039
• P040
• P041
• P042
• P043
• P044
• P045
• P046
• P048
• P051
• P052
• P053
• P055
• P056
• P058
• P060
• P061
• P062
• P063
• P064
• P065
• P066
• P067
• P068
• P070
• P071
• P073
• P074
• P075
• P080
• P092
• P096
• P097
• P098
• P099