3.8l (3800 VIN [c]) ECM Tests W/codes Buick Riviera VII

ELECTROSTATIC DISCHARGE WARNINGS

STATIC CHARGE (VOLTS)

TEST TYPE SELECTION

Having selected a system, the first available test type will be displayed (i.e. "ECM DATA"). When making the selection of test type, the following are available test type alternatives.

1. Pressing the "LEVEL" key pad will stop test type selection and return display to next available system selection.
2. Pressing the "NO" key pad will display the next available test type for the selected system. This allows the display to be stepped through all available test type choices. This list of systems can be repeated following the end of system list.
3. Pressing the "YES" key pad will select the displayed test type. At this point, the display will either indicate that the selected test type is in progress or the first of several specific tests will appear. If "NO DEVICES" appears, no test is available.

TEST SELECTION

Selection of "DATA", "INPUTS", "OUTPUTS", or "OVERRIDE" test types will result in the first available test being displayed. If dashes appear, this test is not permitted with the engine running. Turn engine off and begin again.

The 4 characters of the display will contain a test code to identify the selection. The first 2 are letters which identify the system and test type (e.g., ED for ECM DATA), and the last 2 characters are letters which identify the system and test type (e.g., ED01 for Throttle Position). While selecting a specific test, any of the following actions may be taken to control the display

1. Pressing the "LEVEL" key pad will stop test selection process and return display to next test type for selected system.
2. Pressing the "NO" key pad will display the next smaller test number for selected test type. If this pad is pressed with lowest test number displayed, highest test number will appear.
3. Pressing the "YES" key pad will display the next larger test number for selected test type. If this key pad is touched with highest test number displayed, lowest test number will appear.

Scheme 542

CODE RESET OR CLEARING SELECTION

Selection of "CODE RESET" test type, will result in the message "CODES CLEAR" being displayed with selected system name above, after "YES" pad has been touched. This message appears for 3 seconds indicating that all stored trouble codes have been erased from memory. After this 3-second message, display will automatically return to next available test type for s selected system.

Scheme 543

ECM & BCM Snapshot

Selection of "SNAPSHOT?" test type will result in the message "SNAPSHOT TAKEN", being displayed with selected system name preceding it, for the ECM. While selecting a specific event, any of the following actions may be taken to continue display.

The "LEVEL" pad can be pressed to return to next level in the same system (the BCM will hold 3 snapshots for codes based on the 3 most recent codes). The "NO" pad will cause display of the next code that triggered a snapshot; or, if there are no other codes, will display the message for a manually triggered snapshot, "TAKE BCM SNAPSHOT?". This message will also be displayed after the 3rd (and last) snapshot held in BCM memory.

Pressing the "YES" pad will cause display to proceed to first available snapshot test type, if code is triggered, or if display reads "SNAPSHOT TAKEN" message for 3 seconds and automatically proceeds to first available snapshot test type, if manually triggered.

From this point "Snapshot Test Type" for both ECM and BCM systems operate the same. The only difference is that ECM has only a manual trigger for snapshot, while BCM has manual trigger and memory for storing snapshot information on last 3 codes set.

The "SNAPSHOT TAKEN" message, on manually trigged snapshots, will appear for 3 seconds, indicating that all system data and inputs have been stored in memory. After 3 seconds display will automatically proceed to first available snapshot test type (e.g. SNAP DATA). While selecting a snapshot test type, any of the following actions may be taken to control display

1. Pressing the "LEVEL" button on CRT will stop test type selection process and return display to next available system selection, or event.
2. Pressing the "NO" button will display next available snapshot test type. This allows display to be stepped through all available choices. The list of snapshot test types can be repeated following display of last choice.
3. Pressing the "YES" button with "SNAP DATA?"/"BXXX DATA?" or "SNAP INPUTS"/"BXXX INPUTS?" displayed will select that test type. Display is now controlled as it would be for non -snapshot data and inputs displays. However, all values and status information represents memorized vehicle conditions.
4. Pressing the "YES" button with "SNAPSHOT?" displayed will again display "SNAPSHOT TAKEN" message, indicating that new information has been stored in memory. Access to this information is obtained the same as previously described.

IPC SEGMENT CHECK

When ignition is turned on and vehicle is in Park, pressing "TEST" button on IPC will cause IPC to sequentially illuminate and darken all segments and telltales in cluster. This helps in determining if any bulbs or segments of instrument cluster vacuum fluorescent display are out, or always on. In order to give technician more time to study the various segments (whenever in the "SERVICE MODE" and not running a test) pressing "TEST" button will run segment check 10 times slower.

EXITING "SERVICE MODE"

To exit the service mode, repeatedly press the "LEVEL" pad until "SERVICE MODE" page disappears or press "END" pad, or turn ignition off. Trouble codes are not erased when this is done.

DATA DISPLAYS

When trouble shooting a malfunction, the ECM and BCM data display can be used to compare the problem vehicle, with a vehicle that is functioning properly. The following is a brief summary of each parameter.

ECM DATA DISPLAY CODES

INPUT DISPLAYS

When trouble shooting a malfunction, the ECM, BCM, or IPC input display can be used to determine if switched inputs are properly interpreted. When one of the input tests is selected, the state of that device is displayed as "HI" or "LO". Basically, "HI" or "LO" represent input terminal voltage for that circuit.

Also, the display indicates if input changed state since it was last tested. If a change occurred, an "X" will appear next to the HI - LO indicator. If a change did not occur, an "O" will remain displayed. The "X" will only appear once per selected input.

ECM INPUT DISPLAY CODES

IPC INPUT DISPLAY CODES

OUTPUT DISPLAYS

When trouble shooting a malfunction, the ECM and BCM output cycling can be actuated regardless of the inputs and normal program instructions. Once a test in outputs is selected, except for ECM IAC, the test will display "HI" or "LO" for 3 seconds in each state indicating the command and output terminal voltage.

ECM OUTPUT DISPLAY CODES

OVERRIDE DISPLAYS

When trouble shooting a malfunction, the BCM override feature allows testing of certain system functions regardless of normal program instructions. Upon selecting a test, that selection's current operation will be represented as a percentage of its full range. This value will be displayed on the CRT below the "EXIT" key pad.

Pressing key pads above or below "OVERRIDE" on the CRT begins the override. When in override, pressing key pad above "OVERRIDE" increases the value, while pressing key pad below decreases the value. Normal program control can be acheived in 3 ways.

1. Selection of another override test will cancel the current override.
2. Selection of another system will cancel the current override.
3. Overriding the value beyond either extreme (0 or 99) will display "---" momentarily and then jump to the normal program control.

The override feature, or test type, is unique in that any other test type within the selected system may be active at the same time. After selection of an override test, pressing the "LEVEL" key pad will allow selection of another test type, yet the CRT will continue to display the selected override. When selecting another test or type, and then pressing the key pads above or below "OVERRIDE", it is possible to monitor the effect of override on different vehicle parameters.

ECM OVERRIDE DISPLAY CODES

TROUBLE CODE DISPLAY

After "SERVICE MODE" is entered, any trouble codes stored in computer memory will be displayed. ECM codes will be displayed first. If no ECM codes are stored, CRT will display "NO ECM CODES" for about 2 seconds.

After ECM codes have been displayed, BCM codes will be displayed. BCM codes will also be accompanied by "CURRENT" or "HISTORY". "HISTORY" indicates that the failure was not present when last tested, "CURRENT" indicates fault still exists. This type of information assists in diagnosis of intermittent problems. If no BCM codes are present, BCM will display "NO BCM CODES" message. Trouble codes for both ECM and BCM will be displayed in numerical succession of lowest to highest numbered code.

TROUBLE CODES

ECM TROUBLE CODES

PRELIMINARY PROCEDURES

Prior to any hardware diagnosis, various system checks should be performed.

1. Check to see if "SERVICE ENGINE SOON" light is working. If this light fails to illuminate when the ignition is turned on and engine is not running, problem could be in power supply circuits to these systems. The "SELF-DIAGNOSTIC CHECK" will direct you to the appropriate diagnostic chart.
2. Can "SERVICE MODE" be accessed? If CRT is not operable, self- diagnostics are not possible. In his case, the "SELF -DIAGNOSTIC SYSTEM CHECK" will direct you to the appropriate diagnostic chart.
3. Are there any trouble code(s) displayed? If a trouble code is identified using self-diagnostics, a problem has been detected by the system which can be corrected by following the appropriately numbered fault code. Codes with the prefix "E", are ECM codes. Codes with the prefix "B", are BCM codes.
4. Perform a visual check of the entire system. Check the suspected wiring and components. Inspect hoses that are difficult to see beneath the compressor, generator, etc. Inspect all related wiring for opens, improper connections, burned or chafed spots, pinched wires, contact with sharp edges or contact with hot exhaust manifolds.

HOW TO USE THIS SECTION

This portion of article is used only AFTER you have checked the following

1. Verify the on-car diagnostics are working by performing appropriate DIAGNOSTIC CIRCUIT CHECK chart for that system.
2. Verify that the ECM and "SERVICE ENGINE SOON" light are functioning properly.
3. Verify that there are no trouble codes stored, or only intermittent ones.
4. Perform FUEL SYSTEM PRESSURE TEST.
5. Perform a careful visual inspection of all systems.

After all checks have been performed, verify customer complaint and locate correct symptom. Check items indicated under that symptom. Not all items listed under each symptom apply to all models and systems. These procedures will normally lead you to a component system on vehicle, such as EGR, EST, TCC, etc. These are covered in component system charts. These charts are listed with a "C" before the number of the chart (C1A, for example).

FUEL SYSTEM PRESSURE TEST

Note. Trouble shooting and diagnosis of fuel system should begin with determining fuel injection system pressure. Before replacing fuel system components, fuel pressure must be relieved from system.

1. Connect Fuel Pressure Gauge (J-34730-1) to fuel pressure connector in fuel rail. To reduce possibility of fuel spillage and possible fire hazard, wrap shop cloth around fitting while connecting or disconnecting gauge.
2. To bleed pressure from system for component replacement, insert bleed hose into an appropriate container and open gauge valve.
3. With gauge installed at fuel rail connector, turn ignition on. With ignition on and engine off, pressure should read 40-47 psi (2.8-3.3 kg/cm 2 ). Start engine. Pressure should drop 3-10 psi (.2-7 kg/cm 2 ). For further details on fuel system pressure testing, proceed to appropriate CHART A7 for that system.

Symptom Definition

"SERVICE ENGINE SOON" light comes on but does not stay on. A stored code may or may not exist.

Possible Cause & Correction

To track down possible causes of an intermittent "SERVICE ENGINE SOON" light check the following items.

1. Check for poor mating of one connector to another. Terminals may not be fully seated. Check for improperly formed or damaged terminals. Check wire to terminal connections.
2. Check for poor connection from coil pack to ground or arcing at spark plug wires or plugs.
3. Check wire from "SERVICE ENGINE SOON" light to ECM for short to ground.
4. Check wire from ALDL terminal "D" for intermittent short to ground.
5. Check for poor connections in ECM ground terminals.
6. Check for loss of trouble code memory. To check code memory, disconnect TPS and run engine at idle until "SERVICE ENGINE SOON" light comes on. Code EO22 should be stored and retained in memory when ignition is turned off. If not, ECM is faulty.
7. Check for electrical system interference caused by a defective relay or an ECM driven solenoid or switch which may cause a sharp electrical surge. This type of problem will normally occur when faulty component is operated.
8. Check for aftermarket parts which may not have been produced to manufacturers' specifications. Solenoids without original-equipment diodes for circuit protection or voltage regulator using transistors instead of silicone-chip circuitry may possibly cause voltage surges (up to 300 volts) in ECM wiring, causing temporary ECM shutdown. ECM shutdown is a normal response to system overvoltage (over 16 volts on most models). ECM will repower when condition ceases to exist. This could cause a flickering "SERVICE ENGINE SOON" light with no codes set in memory.
9. Check for improper installation of electrical accessories such as auxiliary lights or 2-way radios.

Engine cranks okay, but does not start for a long time. Engine eventually starts, may immediately die or run okay.

Check the following items.

1. Check fuel pump relay. To do this, connect test light between fuel pump test terminal and ground. Turn ignition on. Light should illuminate for 2 seconds. If not, see appropriate CHART A5 FUEL PUMP RELAY CIRCUIT for that system.
2. Check for poor quality or water contaminated fuel.
3. Check that TPS is not sticking or binding.
4. Check EGR operation. See appropriate component CHART C7 for that system.
5. Check for a leaking injector.
6. Check that resistance of coolant sensor circuit or coolant sensor is not too high. See CODE EO15 chart.
7. Check ignition system for bare or shorted wires. Check for adequate spark using Spark Tester (ST-125).
8. Check for shorts by spraying plug wires with a fine mist of water.
9. Remove spark plugs and check for wet plugs, cracks, improper gap, burned electrodes or heavy carbon deposits.
10. Check for correct fuel pressure in all speed ranges. See appropriate CHART A7 for that system.
11. A faulty in-tank fuel pump check valve will allow fuel in lines to drain back to tank after engine is stopped. To check this condition, turn ignition off, disconnect fuel pressure line at fuel rail, remove filler cap, and connect a radiator test pump and apply 15 psi (1.0 kg/cm( 2 )) pressure. If pressure will hold for 60 seconds, check valve is okay.
12. Check that PROM in vehicle is correct for that vehicle. Check with dealer for latest application information.
13. Check for restricted exhaust system.

Engine starts okay but dies after brief idle, dies as soon as any load is placed on engine (such as turning on air conditioner or engaging transmission), or on initial driveaway.

Check the following items.

1. Check for proper operation of Idle Air Control (IAC) system. See appropriate component CHART C2 for that system.
2. Check PCV valve for proper operation.
3. Unplug MAF sensor. ECM will substitute a default value for MAF signal. If stall condition is eliminated, replace MAF sensor.
4. Check EGR system for proper operation. See appropriate component CHART C7 for that system.
5. If stall occurs when air conditioner is turned on, check for air conditioner clutch signal to ECM terminal. Voltage at A/C terminal of ECM should be battery voltage when air conditioner compressor clutch is engaged. A high voltage surge due to a shorted compressor clutch diode could cause ECM shutdown.
6. Check for an overcharged air conditioner system.
7. Check for plugged or restricted fuel lines. See appropriate component CHART A7, FUEL SYSTEM DIAGNOSIS for that system.
8. Using Spark Tester (ST-125), check for a weak spark.

Momentary lack of response when accelerator is pushed down. Can occur at all vehicle speeds. Usually occurs when taking off from a stop.

Check the following items.

1. Visually check vacuum hoses for splits, kinks and proper connections, as shown on Vehicle Emission Control Information label. Check ignition wires for cracking, hardness and proper connections at coil pack and spark plugs.
2. Check wires for pinches, cuts, and proper connections.
3. Check that fuel pressure is correct in all speed ranges. See appropriate CHART A7, FUEL SYSTEM DIAGNOSIS for that system. Also check for poor quality or water contaminated fuel.
4. Check for fouled spark plugs.
5. Check that PROM in vehicle is correct for that vehicle. Check with dealer for latest application information.
6. Check for a binding or sticking TPS.
7. Ensure that ECM controlled idle speed is correct.
8. Check EGR system for proper operation. See appropriate component CHART C7 for that system.
9. Disconnect fuel injector electrical connectors. Crank engine and check for injector leaks.
10. Check canister purge system for proper operation.
11. Check charging system output. Repair charging system if voltage is less than 9 volts or greater than 16 volts.
12. Perform injector balance test.

Engine power varies under steady throttle or cruise. Feels like vehicle speeds up and slows down without changing position of accelerator pedal.

Check the following items.

1. Perform DIAGNOSTIC CIRCUIT CHECK.
2. Check that Park/Neutral switch is properly adjusted. See appropriate component CHART C1A.
3. Check for intermittent open or short to ground in Torque Converter Clutch (TCC) circuit. See appropriate component CHART C8 TORQUE CONVERTER CLUTCH for that system.
4. Check for proper operation of canister purge system. See appropriate component CHART C3 for that system.
5. Check for proper operation of ESC system. See appropriate component CHART C5 for that system.
6. Check for proper operation of EGR system. See appropriate component CHART C7 for that system.
7. Check for adequate spark output using Spark Tester (ST-125).
8. Check O2 sensor for lead or RTV sealant contamination. This will cause a false high voltage signal to ECM. ECM will respond by leaning air/fuel ratio.
9. Check in-line fuel filter and replace if dirty or clogged.
10. Check fuel for water contamination. Check that fuel system pressure is correct at all engine speeds. See appropriate CHART A7 FUEL SYSTEM DIAGNOSIS for that system.
11. Remove spark plugs and check for wet plugs, cracks, improper gap, burned electrodes or heavy carbon deposits. Also check condition of distributor cap, rotor and spark plug wires.
12. Check A/C for excessive charge.
13. Check for restricted exhaust system.

Engine delivers less power than expected. Little or no increase in speed when accelerator is depressed.

Check the following items.

1. Perform DIAGNOSTIC CIRCUIT CHECK for that system.
2. Check that air filter and fuel filter are not plugged. Replace if necessary. Check for incorrect fuel pressure. See appropriate component CHART A7 for that system.
3. Check for proper operation of TCC system. See appropriate component CHART C8 for that system.
4. Check ESC system for excessive retard. See appropriate component CHART C5 for that system.
5. Ensure that EGR valve is not open all the time. See appropriate component CHART C7 for that system.
6. Check exhaust system for restrictions, such as a damaged or collapsed pipe, muffler or catalytic converter. See appropriate CHART B-1, RESTRICTED EXHAUST SYSTEM CHECK for that system.
7. Check charging system output. Repair charging system if voltage is less than 9 volts or more than 16 volts.
8. Using Spark Tester (ST-125), check for proper spark.
9. Check engine valve timing and compression.
10. Check engine for a worn camshaft.

Fuel ignites in intake manifold or in exhaust system creating a loud popping noise.

Check the following items.

1. Check for proper valve timing.
2. Check engine for sticking or leaking valves.
3. Using Spark Tester (ST-125 ), check available output voltage.
4. Check for crossfire between spark plugs and spark plug wires.
5. Check for an intermittent ignition system problem.

Engine runs unevenly at idle. If bad enough vehicle will shake. Idle may vary in RPM. Engine idles at incorrect RPM.

Check the following items.

1. Perform DIAGNOSTIC CIRCUIT CHECK.
2. Ensure that throttle linkage and/or TPS are not sticking or binding.
3. Check engine idle speed, both base idle and ECM idle.
4. Check Idle Air Control (IAC) system. Check for foreign material in IAC bore. See DIAGNOSTIC AIDS in appropriate component CHART C2 for that system.
5. Check for proper operation of EGR system. See appropriate component CHART C7 for that system.
6. Check P/N switch circuit. Also make sure that P/N switch is properly adjusted. See appropriate component CHART C1 for that system.
7. Check power steering pressure switch circuit. See appropriate component CHART C1 for that system.
8. Check exhaust system for restrictions, such as a damaged or collapsed pipe, muffler or catalytic converter. See appropriate CHART B1, RESTRICTED EXHAUST SYSTEM CHECK for that system.
9. If rough idle only occurs when engine is hot, check PCV valve for proper operation, check evaporative emission control system, check for proper spark plug gap and check engine compression.

Engine starts but will not run at idle. Engine will run if accelerator is held at part throttle.

Check the following items.

1. Problem is most likely in Idle Air Control (IAC) system. See DIAGNOSTIC AIDS in appropriate code chart for that system.
2. Check EGR system. See appropriate component CHART C7 for that system.
3. Check P/N switch. See appropriate component CHART C1A for that system.
4. Disconnect MAF sensor. If condition is corrected, replace sensor.

Fuel economy, as measured by an actual road test, is noticeably lower than expected. Fuel economy is noticeably lower than was on this vehicle at one time.

Check the following items.

1. Check for a clogged air filter.
2. Check cooling system thermostat for proper heat range and operation.
3. Check coolant sensor for shift in calibration. Use temperature-to-resistance chart in Code EO14 or EO15 chart.
4. Ensure that speedometer is properly calibrated.
5. Check engine compression.
6. Check for dragging brakes.
7. Check A/C for "full time" operation.
8. Check for proper EST and ESC operation. See appropriate component CHART C4 and C5 for that system.
9. Check for proper operation of Torque Converter Clutch (TCC). See appropriate component CHART C8 for that system.
10. Check exhaust system for restrictions, such as a damaged or collapsed pipe, muffler or catalytic converter. See appropriate CHART B1, RESTRICTED EXHAUST SYSTEM CHECK for that system.
11. Check oxygen sensor for silicone or lead contamination.
12. Remove spark plugs and check for wet plugs, cracks, improper gap, burned electrodes or heavy carbon deposits.
13. Ensure that speedometer is properly calibrated.
14. Check engine compression.
15. Check for dragging brakes.

Engine continues to run after ignition is turned off, but runs very rough. If engine runs smoothly, check ignition switch.

Check the following items.

1. Check for binding throttle linkage.
2. Check for leaking injectors. See appropriate component CHART A7 for that system. Check injector balance.
3. Check IAC system. See DIAGNOSTIC AIDS in appropriate code chart or component CHART C2 for that system.
4. Check engine for overheating.

A mild to severe ping, usually worse under acceleration. The engine makes sharp metallic knocks that change with amount of acceleration.

Check the following items.

1. Check for obvious overheating problems.
2. Ensure that initial timing is correct.
3. Check TPS adjustment and operation.
4. Check fuel system for low pressure or volume. See appropriate CHART A7 for that system. Also check for induction air leaks.
5. Ensure that ESC system is operating properly. See appropriate component CHART C5 for that system.
6. Ensure that EGR valve is not open all the time. See appropriate component CHART C7 for that system.
7. Ensure that TCC system is operating properly. See appropriate component CHART C8 for that system.
8. Ensure that correct PROM is installed in ECM.
9. Remove carbon from engine using top engine cleaner.
10. If excessive carbon exists in combustion chamber, check for excessive oil burning due to leaking valve guide seals.
11. Check for incorrect basic engine parts such as camshaft, cylinder heads and pistons.
12. Check that PROM in vehicle is correct for that vehicle. Check with dealer for latest application information.

Vehicle fails emission test. Vehicle may also have excessive "rotten egg" smell (hydrogen sulfide) being emitted from exhaust pipe.

Check the following items.

1. Perform DIAGNOSTIC CIRCUIT CHECK for that system.
2. Check for lead contamination of catalytic converter. Look for removal/tampering at restrictor in fuel filler neck.
3. If emission test shows excessive carbon monoxide (CO) and hydrocarbons (HC) emissions and vehicle also has excessive odor being emitted, check all systems and components that could cause engine to run rich. See DIAGNOSTIC AIDS in appropriate CODE EO45 chart for that system.
4. If emission test shows excessive oxides of nitrogen (NOx) emissions, check all systems and components that could cause engine to run lean or to run too hot. See DIAGNOSTIC AIDS in appropriate CODE EO44 chart for that system.

Scheme 544

Scheme 545

Riviera Wiring Diagram. Scheme 546

The following conditions must be met before testing

1. Engine at operating temperature.
2. Engine in closed loop operation.
3. Engine idling ("Engine Run" column).
4. Test terminal NOT grounded.
5. Scanner or ALDL tool NOT installed.
6. Less than .5 volts. (Varies; Varies within this range; Battery voltage for first 2 seconds; Could also be Black/Pink.

DIAGNOSTIC CIRCUIT CHECK

The Diagnostic Circuit Check is an organized approach to identifying a problem created by an electronic control system malfunction. If after completing diagnostic circuit check and finding on-board diagnostics functioning properly (with no trouble codes displayed), a comparison of "Typical Scan Values", for the appropriate engine, may be used for comparison. The "Typical Values" are an average of display values recorded from normal operating vehicles and are intended to represent what a normal functioning system would display.

Diagnostic Circuit Check Flow Chart. Scheme 547

Chart A1, Schematic - "SES" Light Inoperative. Scheme 548

The "SERVICE ENGINE SOON" light is attached to the IPC. It is powered by ignition "3" circuit No. 39. The ECM completes the ground to turn the light on. The light will be on while engine is not running. With the engine running, a steady light indicates an ECM code is set. When the engine is running and diagnostics are entered, a flashing light indicates the field service mode of the ECM. The system monitor button will not affect the "SERVICE ENGINE SOON" light.

Note. Test numbers refer to numbers on diagnostic chart.

1. This step splits the circuit into 2 sections. A light on after grounding terminal "D", indicates the open is on ECM side of split. A light off, indicates the open is on IPC side of circuit.
2. If test light did not illuminate when connected between ECM terminal "BA6" and ground, ECM will not be powered up. This is a result of an open or short to ground (blown fuse) in circuit No. 439.
3. This test checks if open is in IPC or circuit No. 419. There should be battery voltage at IPC terminal "RBA" when connected to terminal "LT1". Test light should illuminate, indicating circuit No. 419 is complete through ALDL terminal "D" which has been jumpered to ground.
4. This test checks if open is in ECM or circuit No. 419. If test light illuminates when ECM terminal "YC11" is grounded, fault is in a poor terminal contact or a faulty ECM.

Chart A1, Flow Chart - "SES" Light Inoperative. Scheme 549

Diagnostic Aids Schematic. Scheme 550

An intermittent may be caused by a poor connection, rubbed through wire insulation or a wire broken inside insulation. Check for the following

1. Poor Connection. Check at ECM pin "YC11" or IPC connector. Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals and poor terminal to wire connections.
2. Damaged Harness. Inspect harness for damage. If harness appears okay, observe related connectors and wiring harness. A flickering light would indicate the intermittent fault location.

Diagnostic Aids Flow Chart. Scheme 551

Chart A2, Schematic - "SES" Light Won't Go Out. Scheme 552

The "SERVICE ENGINE SOON" light is attached to the IPC. It is powered by ignition "3" circuit No. 39. The ECM completes the ground to turn light on. The light will illuminate while engine is not running. With engine running, a steady light indicates an ECM code is set. When engine is running and diagnostics are entered, a flashing light indicates the field service mode of ECM. The system monitor button will not affect the "SERVICE ENGINE SOON" light.

Note. Test numbers refer to numbers on diagnostic chart.

1. This step verifies that light remains on with engine running and no ECM codes displayed.
2. Unplugging ECM harness connector (Yellow) determines if a short to ground exists in the ECM or somewhere else in circuit. If "SERVICE ENGINE SOON" light remains on, fault is not in ECM.
3. This step removes the IPC to distinguish between a grounded IPC or a grounded circuit No. 419. If test light is illuminated when connected between IPC terminals "RBA" and "LT1", circuit No. 419 is shorted to ground.

Chart A2, Flow Chart -"SES" Light Won't Go Out. Scheme 553

Diagnostic Aids

An intermittent may be caused by a poor connection, rubbed through wire insulation or a wire broken inside insulation. Check for the following

1. Poor Connection. Check at ECM pin "YC11" or IPC connector. Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals and poor terminal to wire connections.
2. Damaged Harness. Inspect harness for damage. If harness appears okay, observe related connectors and wiring harness. A flickering light would indicate intermittent fault location.

Diagnostic Aids Flow Chart. Scheme 554

Chart A3, Schematic - Engine Cranks/Won't Run (1 of 4). Scheme 555

The C(3)I system uses waste spark method of spark distribution. In this type of ignition system, ignition module triggers No. 1 and 4 coil, resulting in both No. 1 and 4 spark plugs firing simultaneously. The No. 1 cylinder is on compression stroke at the same time that No. 4 is on exhaust stroke, resulting in a lower energy requirement to fire No. 4 spark plug. This leaves the remaining high voltage to fire No. 1 spark plug. The sequential fuel injection type of fuel delivery system utilizes 6 separate injector "driver" circuits to activate 6 fuel injectors. While cranking, ECM activates all 6 injector "driver" circuits simultaneously. After a calibrated engine RPM is reached, and a good camshaft signal has been received by ECM, the injection mode of operation is changed to sequential (sprayed in spark plug firing order).

Note. Test numbers refer to test numbers on diagnostic chart.

1. 1) This test verifies that "SES" light operation, TPS and coolant sensor signals are normal. A blinking injector test light verifies that ECM is monitoring C(3)I reference signal and attempting to pulse injectors.
2. 2) The crank sensor has been verified as functioning properly. Performing a fuel pressure test will differentiate between fuel related or ignition system problem.
3. 3) By testing for spark on plug leads 1, 3 and 5, each ignition coil's ability to produce at least 25,000 volts is verified. If engine starts, runs for several seconds and dies repeatedly, conisder this to be no spark at all.
4. 4) Checking faulty coil's control circuit using a test light, will determine whether coil is faulty, or module's internal driver for that coil is at fault.

Chart A3, Flow Chart - Engine Cranks/Won't Run (1 of 4). Scheme 556

CHART A3, ENGINE CRANKS BUT WON'T RUN (2 of 4)

Note. Test numbers refer to test numbers on diagnostic chart.

1. 5) This test checks for battery voltage at circuit No. 639. If voltage was present, "light off" test result was caused by no activation pulse reaching injector connector from ECM.
2. 6) If fuse was blown, check circuit No. 839, which includes fuel pump relay, fuel pump and wiring, to determine cause of high current flow.

Chart A3, Flow Chart - Engine Cranks/Won't Run (2 of 4). Scheme 557

CHART A3, ENGINE CRANKS BUT WON'T RUN (3 of 4)

Note. Test numbers refer to test numbers on diagnostic chart.

1. 7) Test light to 12 volts simulates a reference signal to ECM. This results in an injector test light flash with each contact of test light probe to terminal "D". It may take up to 3 probe contacts to flash test light. If test light flashes, circuit No. 430, ECM and injector driver circuits are functioning properly.
2. 8) If crank sensor signal circuit terminal "A" is momentarily jumpered to ground circuit terminal "C", and engine is cranked without turning ignition off, the response should be an injector test light flash. The ignition module will then transmit fuel control signal to ECM while cranking. Allowing generation of reference signal to ECM terminal "BD8", and ECM to activate injector driver circuit.
3. 9) This test verifies proper sync-signal circuit voltage of 9-12 volts, and a proper ground from C(3)I module to terminal "C" of sensor connector.
4. 10) Determines if reason for incorrect voltage reading was due to fault in circuit No. 645 or faulty C(3)I module.

Chart A3, Flow Chart - Engine Cranks/Won't Run (3 of 4). Scheme 558

CHART A3, ENGINE CRANKS BUT WON'T RUN (4 of 4)

Note. Test numbers refer to test numbers on diagnostic chart.

1. 11) Jumping crank sensor harness terminals "A" and "C" together, simulates a sync signal to ignition module. By jumpering crank sensor harness terminals "B" and "C" together, a crank signal is simulated. This signal will then cause ECM to energize fuel pump relay for 2 seconds (it should click on and off) and injectors should be heard clicking on and off.
2. 12) Verifies a proper crank signal circuit voltage of 9-12 volts and a good ground from ignition module to terminal "C" of sensor connector.
3. 13) Determines if reason for incorrect voltage reading was due to a fault in circuit No. 643, an open in circuit No. 645, or a faulty ignition module.

Chart A3, Flow Chart - Engine Cranks/Won't Run (4 of 4). Scheme 559

Chart A5, Schematic - Fuel System Electrical Test (1 of 2). Scheme 560

When ignition is turned on, ECM will energize fuel pump relay, which completes circuit to in-tank fuel pump. It will remain on as long as engine is cranking or running, and ECM is receiving C(3)I reference pulses. If there are no reference pulses, ECM will de-energize fuel pump relay within 2 seconds after key is turned on and engine is not running.

The fuel pump will deliver fuel to fuel rail and injectors, then to pressure regulator, where system pressure is controlled. Excess fuel pressure is by-passed back to fuel tank. When engine is shut off, fuel pump can be turned on by applying battery voltage to test terminal located in engine compartment. Improper fuel system pressure may contribute to one or all of the following symptoms

1. Cranks but won't run.
2. Code EO44 or EO45.
3. Cuts out, may feel like ignition problem.
4. Hesitation, loss of power or poor fuel economy.

Note. Test numbers refer to test numbers on diagnostic chart.

1. 1) If fuse is blown, a short to ground in circuits No. 120 and 639, or fuel pump itself is cause of problem.
2. 2) Determines if fuel pump circuit is being controlled by ECM. The ECM should energize fuel pump relay. When engine is not cranking or running with key on, ECM should de-energize relay within 2 seconds after ignition is turned on.
3. 3) This test activates fuel pump if circuit No. 120 wiring is okay. If pump runs, problem is basic fuel delivery.
4. 4) This test will determine if a short to ground in circuit No. 120 caused fuse to blow. To prevent an incorrect diagnosis, ensure fuel pump is disconnected before test.
5. 5) Checks for short to ground in fuel pump relay harness circuit No. 639.

Chart A5, Flow Chart - Fuel System Electrical Test (1 of 2). Scheme 561

CHART A5, FUEL SYSTEM ELECTRICAL TEST (2 of 2)

Note. Test numbers refer to test numbers on diagnostic chart.

1. 6) Checks for open in fuel pump relay ground, circuit No. 450.
2. 7) Determines if ECM is in control of fuel pump relay through circuit No. 465 (terminal "A").
3. 8) The fuel pump control circuit includes an engine oil pressure switch with a separate set of normally open contacts. The switch closes at about 4 psi of oil pressure and provides a second battery voltage feed path to fuel pump. If relay fails, fuel pump will operate using battery voltage supplied by closed oil pressure switch.

This step checks oil pressure switch, ensuring that it provides battery voltage to fuel pump should pump relay fail. A failed fuel pump relay will result in extended engine crank time, because of time required to build sufficient oil pressure to close oil pressure switch, and activate fuel pump. There may be circumstances when relay has failed, but engine will not crank fast enough to build sufficient oil pressure to close switch. This, or a faulty oil pressure switch, can result in an "Engine Cranks But Won't Run" condition.

Chart A5, Flow Chart - Fuel System Electrical Test (2 of 2). Scheme 562

CHART A7, FUEL PRESSURE TEST (1 of 2)

The fuel pump will deliver fuel to fuel rail and injectors and then to pressure regulator, where system pressure is controlled. Excess fuel pressure is by-passed back to fuel tank. The fuel pump test terminal is located in the engine compartment. Fuel pump can be turned on by applying battery voltage to test terminal.

Improper fuel system pressure may contribute to one or all of the following symptoms

1. Cranks but won't run.
2. Code 44 or 45.

Note. Test numbers refer to test numbers on diagnostic chart.

Note. Test numbers refer to test numbers on diagnostic chart.

Scheme 563

1. 1) Start engine. With ignition on and engine running, pump pressure is regulated by spring pressure and throttle body vacuum within pressure regulator assembly. Turn ignition off for 10 seconds. Pressure should not leak down after fuel pump is shut off.
2. 2) When engine is idling, vacuum is high and is applied to fuel pressure regulator diaphragm. This will overcome regulator spring pressure, resulting in a lower fuel pressure.
3. 3) The application of 12-14 in. Hg vacuum to pressure regulator should result in reduced fuel pressure.
4. 4) Fuel pressure that leaks down may be caused by one of the following conditions: In-tank fuel pump check valve not holding. Pump coupling hose leaking. Fuel pressure regulator valve leaking. Injector sticking open. (Scheme 563): Chart A7, Flow Chart - Fuel Pressure Test (1 of 2)

CHART A7, FUEL PRESSURE TEST (2 of 2)

Improper fuel system pressure may contribute to one or all of the following symptoms

1. Cranks but won't run.
2. Code EO44 or EO45.
3. Cuts out, may feel like ignition problem.
4. Hesitation, loss of power or poor fuel economy. NOTE: Test numbers refer to test numbers on diagnostic chart.

1. 5) If fuel system has pressure, but is less than specification, condition may be caused by one of the following: Regulated pressure, but less than specification. The amount of fuel to injectors is okay, but pressure is too low. The fuel system will operate lean and may set Code EO44. Also, hard starting cold and overall poor performance condition may exist. Restricted fuel flow causing pressure drop. Normally, vehicle with fuel pressure of less than 24 psi (1.7 kg/cm 2 ) at idle will not be driveable. If pressure drop occurs only while driving, engine will normally surge and shut off as pressure begins to drop rapidly.
2. 6) Restricting fuel return line allows fuel pump to develop its maximum pressure (dead head pressure). When battery voltage is applied to pump test terminal, pressure should be greater than 75 psi (5.2 kg/cm 2 ).
3. 7) This test determines if high fuel pressure is due to a restricted fuel return line or a pressure regulator problem.

Chart A7, Flow Chart - Fuel Pressure Test (2 of 2). Scheme 564

CHART B1, RESTRICTED EXHAUST SYSTEM CHECK

Before any components are replaced, exhaust system must be checked for restrictions. Check at O2 sensor procedure may be used to diagnose condition.

1. Raise engine speed to 2500 RPM and observe exhaust system backpressure gauge. Reading should not exceed 1.25 psi (.09 kg/cm 2 ).
2. If during step 1), specification is exceeded, exhaust system restriction is indicated.
3. Check complete exhaust system for collapsed pipe, heat distress and possible internal muffler failure.
4. If none of the conditions in step 4) exist, check for restricted catalytic converter. Replace if necessary.

CHART C2A, INJECTOR BALANCE TEST

Note. If it is determined that injectors are dirty, they should be cleaned using approved injector cleaning procedures prior to performing this test. Complete CHART A7, FUEL SYSTEM DIAGNOSIS before starting this test.

The injector balance test is used to pulse injector for a precise amount of time, spraying a measured amount of fuel in intake manifold. As each injector is pulsed, a drop in fuel rail pressure occurs. This pressure drop can be recorded and compared to other injectors. An injector that has a pressure drop difference of 1.5 psi (.11 kg/cm 2 ) or more, greater or less than other injectors, should be considered faulty.

Note. Allow engine to cool down to avoid irregular readings due to "Hot Soak" fuel boiling. In order to prevent flooding, the INJECTOR BALANCE TEST should not be repeated more than once, without starting and running engine.

1. With ignition off, connect Fuel Pressure Gauge (J34730-1 ) to pressure tap. Unplug harness connector at all injectors. Connect Injector Tester (J34730-3 ) to one of the injectors. On turbocharged engines, use adapter harness supplied with injector tester to pulse injectors that are not accessible.
2. Follow manufacturer's instructions for use of the adapter harness. Ignition should be turned off for at least 10 seconds to complete ECM shutdown cycle.
3. Turn ignition on. Fuel pump should run at least 2 seconds after ignition is turned on. Bleed air from gauge and hose to ensure accurate gauge reading. Repeat this procedure until all air is bled from system. Turn ignition off for at least 10 seconds.
4. Turn ignition on again to bring fuel pressure to maximum. Record initial pressure reading. Energize tester one time and note pressure drop at lowest point.
5. Disregard any slight pressure drop after low point is reached. Subtracting second pressure reading from initial reading indicates amount of injector pressure drop.
6. Repeat test step 4) on each injector and compare amount of pressure drop. Recheck injectors that do not read within pressure drop range. Replace injector(s) that fail second check.
7. If injectors are all okay, plug in harness connectors and review SYMPTOMS in ECM/BCM THEORY & OPERATION section.

Chart C2, Schematic - IAC Valve Check. Scheme 565

Note. Test numbers refer to test numbers on diagnostic charts.

1. Continue with test, even if engine will not idle. If idle is too low, data ED22 will display 80 or more counts, or steps. If idle is high, it will display zero counts. Occasionally an erratic or unstable idle may occur. If engine speed varies 200 RPM or more (up and down), disconnect IAC. If condition is unchanged, IAC is not at fault.
2. When engine was stopped, IAC valve is retracted (more air) to a fixed "Park" position for increased airflow and idle speed, during next engine start. Data ED22 will display 100 or more counts.
3. Ensure that IAC valve is unplugged prior to this test. Test light will confirm ECM signals by a steady or flashing light on all circuits.
4. There is a remote possibility that one of the circuits is shorted to voltage, which would have been indicated by a steady light. Unplug ECM and turn ignition on. Probe terminals to check for this condition.

A slow unstable idle may be caused by a system problem than cannot be overcome by the IAC. The data ED22 counts will be greater than 60 if too low, and zero counts if too high.

If the engine has another source of air to intake mainfold, ECM will compensate by extending IAC. IAC counts may be zero as the ECM tries to maintain desired idle. For other causes check the following

1. System too lean - Idle speed may be too high or too low, or engine running speed may vary up and down, and unplugging IAC does not help. A Code EO44 may have been set. The data ED07 will read an oxygen sensor output less than .3 volt. Check for low regulated fuel pressure or water in fuel. A lean exhaust, with an oxygen sensor output fixed greater than .8 volts indicates sensor contaminated with silicone. This may also set Code EO45.
2. System too rich - Idle speed too low. Data ED22 counts will be usually greater than 80. System is obviously rich and may exhibit Black exhaust smoke. The data ED07 will read an oxygen sensor signal fixed greater than .8 volt. Check for high fuel pressure or injector leaking or sticking.
3. Throttle body - Remove IAC and inspect for foreign material or evidence of IAC valve dragging the bore.
4. See TROUBLE SHOOTING in ECM/BCM THEORY & OPERATION.

Chart C2, Flow Chart - IAC Valve Check. Scheme 566

Chart C3, Schematic - Canister Purge Check. Scheme 567

The purge solenoid is energized (purge on) if the diagnostic test terminal is grounded with the engine stopped or if following conditions are met

1. Engine run time is more than 30 seconds.
2. Coolant temperature more than 158°F (60°C).
3. "Closed Loop" operation.

Note. Test numbers refer to test numbers on diagnostic charts.

1. Checks to see if solenoid is opened or closed. Solenoid is normally de-energized in this test, indicating it should be closed.
2. This test completes functional check by grounding test terminal. This should normally energize solenoid and allow vacuum to drop (purge on).
3. This test checks for open or shorted solenoid circuit. Solenoid coil resistance must measure greater than 20 ohms.

Chart C3, Flow Chart - Canister Purge Check. Scheme 568

Chart C4F-1, Schematic - C(3)I Misfire At Idle. Scheme 569

Note. Test numbers refer to test numbers on diagnostic charts.

1. If misfire problem exists under load only, see CHART C4F-2. Engine RPM should drop equally on all plug leads.
2. Spark Tester (ST-125 ) must be used because it is essential to verify adequate available secondary voltage (25,000 volts) at spark plug.
3. If ignition coils are carbon tracked, the coil tower spark plug wire nipples may be damaged.
4. By checking secondary resistance, a coil with an open secondary may be located.
5. By installing a normally operating coil pack, a determination can be made as to fault being the coil or ignition module.

Chart C4F-1, Flow Chart - C(3)I Misfire At Idle. Scheme 570

Chart C4F-2, C(3)I Misfire Under Load. Scheme 571

Note. Test numbers refer to test numbers on diagnostic charts.

1. If misfire problem exists at idle only, see CHART C4F-1.
2. Spark Tester (ST-125 ) must be used because it is essential to verify adequate available secondary voltage (25,000 volts) at the spark plugs. Spark should jump the tester gap on all 6 leads. This simulates a "load" condition.
3. If ignition coils are carbon tracked, coil tower spark plug wire nipples may be damaged.
4. By installing a normally operating coil, a determination can be made as to the fault being the coil or ignition module.

Chart C4F-2, Flow Chart - C(3)I Misfire Under Load. Scheme 572

Chart C5 Schematic - ESC System Check. Scheme 573

The knock sensor is used to detect engine detonation and ECM will retard the electronic spark timing based on signal being received. The circuitry, within the knock sensor, causes ECM's supplied 5-volt signal to be pulled down so that under a no knock condition, circuit No. 496 would measure about 2.5 volts. The knock sensor produces an AC signal, which rides on the 2.5 volts (DC voltage). The amplitude and frequency are dependent upon the knock level.

The MEM-CAL used with this engine, contains functions which were part of remotely mounted ESC modules used on other GM vehicles. The ESC portion of the MEM-CAL, sends a signal to other parts of the ECM which adjusts spark timing to retard spark and reduce detonation.

Note. Test numbers refer to test numbers on diagnostic charts.

1. With engine idling, there should not be a knock signal present at ECM, because detonation is not likely to occur under a no load condition.
2. Tapping engine lift hook should simulate a knock signal to determine if sensor is capable of detecting detonation. If no knock is detected, try tapping on engine block closer to sensor before replacing sensor.
3. If engine has an internal problem which is creating a knock, knock sensor may be responding to internal failure.
4. This test determines if knock sensor is faulty or if ESC portion of MEM-CAL is faulty. If it is determined that MEM-CAL is faulty, ensure that it is properly installed and latched into place. If not properly installed, repair and retest.

While observing knock signal on data ED17, there should be an indication that knock is present, when detonation is audible. Detonation is most likely to occur under high engine load conditions. Also see TROUBLE SHOOTING in ECM/BCM THEORY & OPERATION.

Chart C5, Flow Chart - ESC System Check. Scheme 574

Chart C7, Schematic - EGR Flow Check. Scheme 575

The digital EGR valve is designed to accurately supply EGR to an engine independent of intake manifold vacuum. The valve controls EGR flow from the exhaust to intake manifold through 3 orifices which increment in size to produce 7 combinations. When a solenoid is energized, the armature, with attached shaft and swivel pintle, is lifted, opening the orifice. The flow accuracy is dependent on metering orifice size only, which results in improved control.

Note. Test numbers refer to test numbers on diagnostic charts.

If a code is set, inspect EGR for damage. Start and idle engine, enter ECM overrides data ES02, ES03 and ES04. You should be able to discern a change in engine RPM as the ECM turns on the EGR.

Data ES02 should result in a small change and data ES04 in a large change in RPM. The engine may stall when data ES04 is turned on.

Chart C7, Flow Chart - EGR Flow Check. Scheme 576

Chart C8A, Schematic - Torque Converter Clutch (TCC). Scheme 577

Note. Test numbers refer to test numbers on diagnostic charts.

1. "LO" display confirms that 4th gear switch is closed.
2. At 45 MPH, transaxle 4th gear switch should open, resulting in IPC displaying "HI".
3. Entering ECM diagnostics output data EO01 should cause the solenoid to cycle on and off at 3 second intervals. This test checks the capability of the ECM to control the solenoid driver circuit. Solenoids are turned on or off by ECM internal electronic switches, called "drivers". Each driver is part of a group of 4, called Quad-Drivers. Using an ohmmeter, check solenoid coil resistance of TCC. Coil resistance must measure greater than 20 ohms.

Chart C8A, Flow Chart - Torque Converter Clutch (TCC). Scheme 578

Chart C12A, Schematic - Coolant Fan Check (Riviera). Scheme 579

All applications use 2 fans and 3 relays.

1. Low Speed - The low speed coolant fan relay is energized by the ECM. The ECM will engergize the low speed relay when coolant temeperature exceeds 208°F (101°C) or when requested to do so by BCM, based on an A/C high side temperature, BCM data BD27, which exceeds 122°F (50°C).
2. High Speed - The high speed coolant fan relay is energized by the ECM. The ECM will energize both high speed relays when coolant temperature exceeds 226°F (108°C) or when requested to do so by BCM based on an A/C high side temperature, BCM data BD27, which exceeds 149°F (65°C).

Note. Test numbers refer to test numbers on diagnostic charts.

1. Codes EO14 or EO15 could indicate coolant system or sensor operation is not normal, so fan operation cannot be checked correctly.
2. ECM Code EO09 grounds "LO" speed relay through ECM for 3 seconds on, and 3 seconds off. "LO" speed fan should be on for 3 seconds and off for 3 seconds.
3. ECM Code EO10 grounds high speed relay through ECM for 3 seconds on and 3 seconds off. High speed fan should be on for 3 seconds and off for 3 seconds.

Chart C12A, Flow Chart - Coolant Fan Check (Riviera). Scheme 580

CHART C12B, COOLANT FAN CHECK (RIVIERA)

Note. Test numbers refer to test numbers on diagnostic charts.

1. Test light should illuminate, as harness terminal No. 2 has battery voltage with ignition switch in "ON" position. Terminal No. 4 has battery voltage at all times.
2. Test light should illuminate for 3 seconds and turn off for 3 seconds, as Code EO09 cycles fan on/off at 3 second intervals.
3. Jumpering harness terminals No. 1 and 4 by-passes relay. If fan runs, relay is faulty.
4. Cycling of the test light verifies circuit No. 532 and 804 are okay.

Chart C12B, Flow Chart - Coolant Fan Check (Riviera). Scheme 581

CHART C12C-A, COOLANT FAN - NO HIGH SPEED REAR FAN

Note. Test numbers refer to test numbers on diagnostic charts.

1. Test light should be on, as harness terminal No. 5 has battery voltage with ignition switch in "ON" position. Terminal No. 1 has battery voltage at all times.
2. Test light should be on for 3 seconds and off for 3 seconds, as Code EO10 cycles fan on/off at 3 second intervals.
3. Jumpering harness terminals No. 1 and 4 by-passes relay. If fan runs, relay is faulty.
4. Cycling of the test light verifies circuits No. 533 and 804 are okay, indicating fan motor is faulty.

Chart C12C-A, Flow Chart - Coolant Fan Check No High Speed Rear Fan. Scheme 582

CHART C12C-B, COOLANT FAN - NO HIGH SPEED FRONT FAN

Note. Test numbers refer to test numbers on diagnostic charts.

1. Test light should be illumate, as harness terminal No. 5 has battery voltage with ignition switch turned to "ON" position. Terminal No. 1 has battery voltage at all times.
2. Test light should be illuminated for 3 seconds and turn off for 3 seconds as Code EO10 cycles fan on/off at 3 second intervals.
3. Jumpering harness terminals No. 1 and 4 by-passes relay. If fan runs, relay is faulty.
4. Cycling of test light indicates circuits No. 533 and 804 are okay.

Chart C12C-B, Coolant Fan - No High Speed Front Fan. Scheme 583

CHART C12D, COOLANT FAN CHECK "ON" AT ALL TIMES

Note. Test numbers refer to test numbers on diagnostic charts.

1. Checks to see if circuits No. 535 or 536 are shorted to ground, which would cause fan relay(s) to be energized at all times.
2. High temperature will cause A/C high side temperature sensor, due to A/C system temperature, to exceed the 122°F (50°C) point and BCM will request low speed fan at all times.
3. Coolant fans will come on when engine is started, but should go off when system stabilizes. Coolant fans should be off when A/C high side temperature switch is disconnected and coolant temperature is less than 208°F (98°C).

Coolant fans should be off if coolant temperature is less than 208°F (98°C) and/or if A/C high side temperature is less than 122°F (50°C). Disconnecting A/C high side temperature sensor should result in BD27 reading less than -30°C. If not, see BCM Code B111 for diagnosis. Disconnecting coolant temperature sensor should cause BD21 to read less than -30°C also. If not, see ECM Codes EO14 or EO15. BD27 should read about 122°F (50°C) when A/C system high side pressure is about 160 psi. Comparing these might indicate defective sensor.

Chart C12D, Flow Chart - Coolant Fan Check Always "On". Scheme 584

Self-Diagnostic System Check. Scheme 585

Chart B1, Cannot Enter Diagnostics. Scheme 586

Chart B2, CRTC Or Data Problem. Scheme 587

Chart B2, CRTC Or Data Problem. Scheme 588

Chart B3, No Communication. Scheme 589

Chart B4, No Communication. Scheme 590

Chart B5, CRTC Problem. Scheme 591

Chart B6, No Communication To IPC W/Only Radio Functions. Scheme 592

Chart B7, Schematic - BCM Problem. Scheme 593

Chart B7, Flow Chart - BCM Problem. Scheme 594

CHART B8, Loss Of Logic - 7 Volts. Scheme 595

Chart C1, CRT Problem. Scheme 596

Chart C2, Schematic - No Picture. Scheme 597

Chart C2, Flow Chart - No Picture. Scheme 598

Chart C3, No Switches Respond Or Beeper Problem. Scheme 599

Chart C4, Some Switches Do Not Respond. Scheme 600

Chart C5, Picture Rolls. Scheme 601

Note. If you have not performed the self-diagnostic system check, start there first

COLOR CRT TROUBLE SHOOTING CHART

Note. When All Diagnosis and Repair are Completed, Clear Codes and Verify Operation

Code EO13, Schematic - Open Oxygen Sensor Ckt. Scheme 602

Note. Test numbers refer to numbers on diagnostic chart.

1. Code EO13 will set under the followig conditions: No Codes EO21 or EO22. Engine at normal operating temperature. Engine run time greater than 40 seconds. O2 signal voltage ED07 display, steady between .35 and .55 volt. Throttle position sensor greater than .55 volt. All conditions must be met for about 30 seconds. If the above conditions for a Code EO13 exists, the system will not go to "closed loop".
2. This will determine if the sensor or the wiring is the cause of the Code EO13.
3. In performing this test, use only a high impedence digital volt/ohmmeter. This test checks the continuity of circuits No. 412 and 413. If circuit No. 413 is open, the ECM voltage on circuit No. 412 will be greater than .6 volt (600 mV).

An intermittent may be caused by a poor connection, rubbed through wire insulation or a wire broken inside the insulation. Check for the following conditions

1. Poor Connection or Damaged Harness. Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal to wire connection and damaged harness.
2. Intermittent Test. If connections and harness check okay, observe ED15 display, O2 sensor voltage while moving related connectors and wiring harness, with warm engine running at part throttle in "closed loop". If the failure is induced, the O2 sensor voltage reading will change from its normal fluctuating voltage (greater than .60 volt and less than .30 volt) to a fixed value around .45 volt. This may isolate the location of malfunction.

Code EO13, Flow Chart - Open Oxygen Sensor Ckt. Scheme 603

Code EO14, Schematic - Coolant Sensor Temperature Too High. Scheme 604

Note. Test numbers refer to numbers on diagnostic chart.

1. Code EO14 will set if signal voltage indicates a coolant temperature greater than 282°F (130°C) for .4 second.
2. This test will determine if circuit No. 410 is shorted to ground which will cause the conditions for Code EO14. If Code EO14 is set, the ECM will use 119°F (48.6°C) for fuel control.

Check for the following conditions

1. Poor Connection or Damaged Harness. Inspect ECM harness connectors for backed out terminal "YD4", improper mating,broken locks, improperly formed or damaged terminals, poor terminal to wire connection and damaged harness.
2. Intermittent Test. If connections and harness check okay, observe ED04 display (coolant temperature) while moving related connectors and wiring harness. If the failure is induced, the coolant temperature display will change. This may help toisolate location of malfunction.
3. Shifted Sensor. The temperature-to-resistance value scale may be used to test the coolant sensor at various temperature levels to evaluate the possibility of a shifted (mis-scaled) sensor, which may result in driveability complaints.

Code EO14, Flow Chart - Coolant Sensor Temperature Too High. Scheme 605

Code EO15, Schematic - Coolant Sensor Temperature Too Low. Scheme 606

Note. Test numbers refer to numbers on diagnostic chart.

1. Code EO15 will set if signal voltage indicates a coolant temperature less than -40°F (-40°C) for at least 2 seconds.
2. This test simulates a Code EO14. If the ECM recognizes the low signal voltage (high temperature), and the CTS display reads 130°C, the ECM and wiring are okay.
3. This test will determine if circuit No. 410 is open. There should be 5 volts present at sensor connector if measured with a digital volt/ohmmeter. If Code EO15 is set, the ECM will use 119°F (48.6°C) for fuel control.

Check for the following conditions

1. Poor Connection or Damaged Harness. Inspect ECM harness connectors for backed out terminal "YD4", improper mating, broken locks, improperly formed or damaged terminals, poor terminal to wire connection and damaged harness.
2. Intermittent Test. If connections and harness check okay, observe ED04 display (coolant temperature) while moving related connectors and wiring harness. If the failure is induced, the coolant temperature display will change. This may help to isolate location of malfunction.
3. Shifted Sensor. The temperature-to-resistance value scale may be used to test the coolant sensor at various temperature levels to evaluate the possibility of a shifted (mis-scaled) sensor, which may result in driveability complaints.

A faulty connection, or an open in circuits No. 410 or 452 will result in a Code EO15. If Code EO23 is also set, check circuit No. 452 for faulty wiring or connections. Check terminals at sensor for good contact. Refer to INTERMITTENTS in ECM/BCM THEORY & OPERATION.

Code EO15, Flow Chart - Coolant Sensor Temperature Too Low. Scheme 607

Code EO16, Schematic - Battery Voltage Too High. Scheme 608

The ECM monitors battery or system voltage on circuit No. 480 to terminals "BB1" and "BC16". If ECM detects voltage greater than 16 volts, it will turn the "SERVICE ENGINE SOON" light on and set a Code EO16 in memory.

Note. Test numbers refer to numbers on diagnostic chart.

1) Test generator output to determine proper operation of voltage regulator. Run engine at moderate speed and measure voltage across battery. If greater than 16 volts, repair generator.

An intermittent may be caused by a poor connection, rubbed through wire insulation or a wire broken inside the insulation. Check for the following conditions

1. Poor Connection or Damaged Harness. Inspect harness connectors for backed out terminals "BC16" or "BB1", improper mating, broken locks, improperly formed or damaged terminals, poor terminal to wire connection and damaged harness.
2. Intermittent Test. If connections and harness check okay, observe ED10 display, while moving related connectors. If the failure is induced, the battery voltage will abruptly change. This may help to isolate the location of the malfunction. An engine stall while manipulating the harness indicates that the ECM has lost voltage at terminal "BC16" or "BB1". Check for loose connectors in circuit No. 480.

Note. Charging battery with a battery charger and starting the engine may set a Code EO16.

Code EO16, Flow Chart - Battery Voltage Too High. Scheme 609

Code EO21, Schematic - TPS Signal Voltage High. Scheme 610

Note. Test numbers refer to numbers on diagnostic chart.

1. Code EO21 will set under the following conditions occur: Engine is running and airflow is less than 15 gm/sec. TPS signal voltage is greater than 2.5 volts. Code EO33 or EO34 not present at first start up. All conditions met for 5 seconds. With closed throttle, ignition on or engine at idle, voltage at terminal "3D13" should be .34-.46 volt. If not, TPS should be adjusted to specification.
2. With TPS sensor unplugged, TPS voltage should go low and Code EO22 will set, if ECM and wiring is okay.
3. Probing circuit No. 452 with a test light checks sensor ground circuit. A faulty sensor ground circuit will cause a Code EO21.

An ED01 display reads throttle position in volt. With closed throttle, ignition on or at idle, voltage should be .34-.46 volt. If not, adjust TPS to specification. An open in circuit No. 452 will result in a Code EO21. Check for the following conditions

1. Poor Connections or Damaged Harness. Inspect ECM harness connectors for backed out terminal "YD13", improper mating, broken locks, improperly formed or damaged terminals, poor terminal to wire connections and damaged harness.
2. Intermittent Test. If connections and harness check out okay, monitor TPS voltage on ED01 display while moving related connectors and wiring harness. If failure is induced, coolant temperature display will change. This may help to isolate location of malfunction.
3. TPS Scaling. Observe TPS voltage display while depressing accelerator pedal with engine stopped and ignition on. Display should vary from closed throttle TPS voltage when throttle was closed, to greater than 4 volts when throttle is held at WOT position.

Code EO21, Flow Chart - TPS Signal Voltage High. Scheme 611

Code EO22, Schematic - TPS Signal Voltage Low. Scheme 612

Note. Test numbers refer to test numbers on diagnostic chart.

1. Code EO22 will set if engine is running and TPS signal voltage is less than .2 volt for 4 seconds.
2. Simulates Code EO21. If ECM recognizes high signal voltage, ECM and wiring are okay.
3. With closed throttle, ignition on or engine at idle, voltage at terminal "YD13" should be .34-.46 volt. If voltage is not okay, check TPS adjustment.
4. Simulates a high signal voltage. Checks circuit No. 417 for open.

The ED01 display reads throttle position in volts. Voltage should increase at a steady rate as throttle is moved toward WOT. An open or short to ground in circuit No. 416 or 417 will result in a Code EO22. Check for the following conditions

1. Poor Connections. Inspect ECM harness connectors for backed out terminal "YD13", improper mating, broken locks, improperly formed or damaged terminals, poor terminal-to-wire connection and damaged harness.
2. Intermittent Test. If connections and harness checks out okay, monitor TPS voltage while moving related connectors and wiring harness. If failure is induced, coolant temperature display will change. This may help to isolate location of malfunction.
3. TPS Scaling. Observe TPS voltage display while depressing accelerator pedal with engine stopped and ignition on. Display should vary from closed throttle TPS voltage when throttle was closed, to greater than 4 volts when throttle is held wide open.

Code EO22, Flow Chart - TPS Signal Voltage Low. Scheme 613

Code EO23, Schematic - MAT Sensor Signal Voltage High. Scheme 614

Note. Test numbers refer to test numbers on diagnostic chart.

Code EO23 will set if a signal voltage indicates a manifold air temperature less than -40°F (-40°C) for 4 seconds. Due to the conditions necessary to set a Code EO23, the "Service Engine Soon" (SES) light will stay only while fault is present.

1. The ED23 display may not be used to diagnose this fault, due to the ECM transmitting "default" values. A Code EO23 will set, due to an open sensor, wire or connection. This test determines if wiring and ECM are okay.
2. If resistance is greater than 25,000 ohms, inspect air cleaner for ice. If ice is not present, replace sensor.

An intermittent may be caused by a poor connection, rubbed through wire insulation or a wire broken inside the insulation. Check for the following conditions

1. Poor Connection or Damaged Harness. Inspect harness connectors for backed out terminals "BA5", "YD11", improper mating, broken locks, improperly formed or damaged terminals, poor terminal to wire connection and damaged harness.
2. Intermittent Test. If connections and harness check okay, observe ED23 display, while moving related connectors and wiring harness with warm engine running at part throttle in closed loop. If the failure is induced, the MAT display may change the 40°C default value to the proper ambient temperaure reading. This may help to isolate location of the malfunction.

Code EO23, Flow Chart - MAT Sensor Signal Voltage High. Scheme 615

Code EO24, Schematic - Vehicle Speed Sensor (VSS) Ckt. Scheme 616

Note. Test numbers refer to numbers on diagnostic chart.

1. Code EO24 will set if vehicle speed signal is less than 3 MPH when the following conditions exist: Engine is running. No Code EO29 or EO31. Vehicle is in 4th gear. Above conditions met for 40 seconds. The PM generator only produces a signal if drive wheels are turning greater than 3 MPH.
2. Before replacing ECM, check MEM-CAL for correct application.

The "On-Board Diagnostic Display" should indicate a vehicle speed whenever the drive wheels are turning greater than 3 MPH. Check circuits No. 400 and 401 for proper connections to ensure they are clean and tight

Code EO24, Flow Chart - Vehicle Speed Sensor (VSS) Ckt. Scheme 617

Code EO25, Schematic - Manifold Air Temperature (MAT) Sensor Ckt (High Temperature Indicated). Scheme 618

Note. Test numbers refer to test numbers on diagnostic chart.

Code EO25 will set if

1. Signal voltage indicates manifold air temperature greater than 275°F (135°C).
2. A vehicle speed is present.
3. Both of the above requirements are met for at least 16 seconds.

Due to the conditions necessary to set a Code EO25, "SERVICE ENGINE SOON" light will only stay on while fault is present.

1) If Code EO25 is current, ED23 display may be used to diagnose this fault. If the fault is current, ECM will transmit 148°C as the data value.

Code EO25, Flow Chart - MAT Sensor Ckt (High Temp Indicated). Scheme 619

Code EO26, Schematic - Quad Driver (QDM) Error. Scheme 620

The ECM is used to control several components such as those illustrated in the mini circuit schematic. ECM controls these devices through the use of a Quad-Driver module (QDM). When the ECM is commanding a component on, the voltage potential of the output circuit will be low (near zero volts). When the ECM is commanding the output circuit to a component off, the voltage potential of the circuit will be high (near battery voltage). The primary function of the QDM is to supply the ground for the component being controlled.

Each QDM has a fault line which is monitored by the ECM. The fault line signal is available on the data stream for "Scan" tester equipment. The ECM will compare the voltage at the QDM based on accepted values of fault line. If the QDM fault detection circuit senses a voltage other than the accepted value, the fault line will go from a low signal on the data stream, to a high signal and a Code EO26 will set if applicable.

Some QDM circuits will switch from low to high normally. Examples: QDM No. 2, if A/C pressure switch closes and turns on high speed coolant fan or QDM No. 3, if brake is depressed. These conditions are normal and no Code EO26 is set. These are accepted conditions. A fault on QDM No. 2 will not set a Code EO26, but diagnosis may be done by ensuring A/C is turned off. Some "Scan" tools will cause a false Code EO26 to set if engine is running and service brake is depressed for over 30 seconds.

Note. Test numbers refer to test numbers on diagnostic chart.

Scheme 621

1. The ECM does not know which controlled circuit caused the Code EO26. This chart will go through each of the circuits to determine which is at fault. This test also checks "SERIVCE ENGINE SOON" light driver and "SERVICE ENGINE SOON" light circuit.
2. QDM fault symptoms: TCC inoperative, Code EO39. EGR inoperative, Codes EO63, EO64 and EO65. Coolant fan on low speed all the time of won't come on at all. Poor driveability due to 100 percent canister purge. (Scheme 621): Code EO26, Flow Chart - Quad Driver (QDM) Error (1 of 3) NOTE: Test numbers refer to test numbers on diagnostic chart.
3. This test will determine which circuit is out of specification. All circuit, except "YC11", "SERVICE ENGINE SOON" light, "YC9", and hot light, should have battery voltage when key is on, engine not running. Diagnostic test terminal is not grounded.

An intermittent may be caused by a poor connection, rubbed through wire insulation or a wire broken inside the insulation. Check for the following condition

1. Inspect ECM harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal to wire connection and damaged harness.

Code EO26, Flow Chart - Quad Driver (QDM) Error (2 of 3). Scheme 622

Note. Test numbers refer to test numbers on diagnostic chart.

4) This test will determine if problem is the circuit of the component. As factory installed ECM is protected with an internal fuse, it is highly unlikely that ECM needs replacement.

Code EO26, Flow Chart - Quad Driver (QDM) Error (3 of 3). Scheme 623

Codes EO27/EO28/EO29 Schematic - 2ND/3RD/4TH Gear Switch Diagnosis. Scheme 624

Gear switches are located inside the transaxle. They are pressure operated switches, that are normally closed. The ECM supplies 12 volts through each selected circuit to switch. In any condition other than the specific gear application, signal line monitors low voltage or low potential. As road speed increases, hydraulic pressure is applied to specific gear clutches, and gear switch opens. During this time, ECM monitors high 12-volt potential and interprets this to indicate that gear is applied. The ECM uses gear signals to control fuel delivery (and TCC).

Note. Test numbers refer to test numbers on diagnostic chart.

Code EO27 will set under the following conditions

1. Circuit No. 581 indicates ground or closed switch when vehicle is in 4th gear operation.
2. Code EO29 not present.
3. Circuit No. 446 is open when engine is first started.
4. Circuit No. 581 indicates ground or closed switch when vehicle is in 4th gear operation.
5. Circuit No. 581 indicates an open (Drive) when the engine is first started.

Code EO28 will set under the following conditions

1. Circuit No. 108 indicates ground or closed switch when vehicle is in 4th gear operation.
2. Circuit No. 108 indicates an open (Drive) when the engine is first started.
3. Circuit No. 446 is open when engine is first started.

Code EO29 will set under the following conditions

1. Circuit No. 446 indicates ground or closed switch when vehicle is in 4th gear operation.
2. Circuit No. 446 indicates an open (Drive) when the engine is first started.

1. DVOM must be used. A test light will not light due to very low current being supplied by ECM.
2. Checks to see if circuit is grounded through switch.
3. Checks for a good, properly operating switch. Also checks circuit within transaxle for an improper ground.

An intermittent may be caused by a poor connection, incorrectly routed harness, rubbed through wire insulation or a wire broken inside insulation. Check for the following

1. Poor Connection at ECM pins. Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals and poor terminal to wire connection.
2. Misrouted Harness. Inspect wiring harness to ensure that it is not too close to high voltage wires, such as spark plug leads.
3. Damaged Harness. Inspect harness for damage. If harness appears okay, observe EI79, EI80 and EI82 displays while moving related connectors and wiring harness. A change in display would indicate the intermittent fault location.

Code EO27/EO28/EO29, Flow Chart - 2ND/3RD/4TH Gear Switch Diagnosis. Scheme 625

Code EO31, Schematic - Park/Neutral Switch Ckt. Scheme 626

The Park/Neutral (P/N) switch contacts are part of the neutral start switch and are closed to ground in Park or Neutral, and open in Drive. The ECM supplies ignition voltage through a current limiting resistor to circuit No. 434 and senses a closed switch when the voltage on circuit No. 434 drops to less than one volt. The ECM uses the P/N signal as one of the inputs to idle air control, EGR and VSS diagnostics.

Code 31 will set under the following conditions

1. If circuit No. 434 indicates P/N (grounded) while in Drive range and 4th gear TCC engaged, EGR would be inoperative, resulting in possible detonation.
2. If circuit No. 434 indicates Drive (open) at start up, a drop in idle may exist when gear selector is moved into Drive range.
3. If transaxle 4th gear switch has an intermittent open, ECM thinks vehicle is in 4th gear and will set Code EO31.

Note. Test numbers refer to test numbers on diagnostic chart.

1. Checks for a closed switch to ground in "PARK" position.
2. Checks for an open switch in Drive range.
3. Ensure that on-board diagnostics EI74 indicates Drive ("HI"), even while wiggling shifter. This will test for an intermittent or misadjusted switch in Drive or Overdrive range.

Code EO31, Flow Chart - Park/Neutral Switch Ckt. Scheme 627

Code EO34, Schematic - Mass Airflow Sensor Ckt. Scheme 628

The Mass Airflow (MAF) sensor measures the flow of air which passes through it in a given time. The ECM uses this information to monitor the operating condition of the engine for fuel delivery calculations. A large quantity of air movement indicates acceleration, while a small quantity indicates deceleration or idle.

The MAF sensor produces a frequency signal, which cannot be easily measured. The sensor can be diagnosed using the procedures in this chart. Code EO34 will set, when either of the following sets of conditions exists

1. Engine running.
2. No MAF sensor signal for 250 milliseconds.
3. Above conditions for greater than 4 seconds.

Note. Test numbers refer to test numbers on diagnostic chart.

1. This step checks to see if ECM recognizes a problem.
2. A voltage reading at sensor harness connector terminal "A" of less than 4 volts, or greater than 6 volts, indicates a fault in circuit No. 492 or poor connections.
3. Verifies that both ignition voltage and a good ground circuit are available.

Check for the following

1. Poor Connection at ECM pin "YD10". Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals and poor terminal to wire connection.
2. Misrouted Harness. Inspect MAF sensor harness to ensure that it is not too close to high voltage wires, such as spark plug leads.
3. Damaged Harness. Inspect harness for damage. If harness appears okay, observe ED21 display while moving related connectors and wiring harness. A change in display would indicate the intermittent fault location.
4. Plugged Air Intake Filter. A WOT acceleration from a stop should cause MAF reading (ED21) to range from about 4.7 at idle, to 100 or greater at the time of 1-2 transmission shift. If not, check for air intake restriction.

Code EO34, Flow Chart - Mass Airflow Sensor Ckt. Scheme 629

Code EO38, Schematic - Brake Switch Ckt. Scheme 630

The ECM monitors the status of brake switch circuits through ECM terminal "BC4". Code EO38 will set under the following conditions

1. Code EO24 is not present.
2. Vehicle speed has been greater than 35 MPH and back to zero MPH several times.
3. Status of circuit No. 420 has not changed state high to low.

Note. Test numbers refer to test numbers on diagnostic chart.

1. This step checks for battery voltage available for circuit No. 420.
2. Checks fuse, switch and circuit for battery voltage.

Code EO38, Flow Chart - Brake Switch Circuit. Scheme 631

Code EO39, Schematic - TCC Ckt. Scheme 632

The ECM controls TCC operation by grounding circuit No. 422 through the QDM. Code EO39 will set under the following conditions

1. Code EO29 is not present.
2. Brake switch is closed (off).
3. TCC is commanded on by ECM.
4. Vehicle is in 4th gear.
5. The engine speed to vehicle speed ratio is outside of its window of operation.
6. All of the above for a time greater than 30 seconds.

Note. Test numbers refer to numbers on diagnostic chart.

1. Checks availability of battery voltage on circuit No. 420.
2. Check fuse, brake switch and battery voltage circuit to the TCC solenoid.

Codes EO26 and EO38 in combination with a Code EO39, would indicate a problem with fuse, circuit No. 139, brake switch or wire ahead of splice. A single Code EO26 is the result of a wire or circuit No. 420 problem between the splice and the ECM, poor connection to ECM connector, or possibly the ECM. A Code EO26 with an Code EO39 is the result of a problem in circuit from splice to ECM. Another cause might be an open or grounded circuit No. 420 ahead of TCC solenoid, a bad TCC solenoid, open or grounded circuit No. 422, bad connections at ECM connector "YC10" or ECM.

Code EO39, Flow Chart - TCC Ckt. Scheme 633

Code EO41, Schematic - CAM Sensor Signal. Scheme 634

Code 41 is set when the following conditions are met

1. Engine is running.
2. Cam sensor signal not received by ECM in last 2 seconds.

Note. Test numbers refer to test numbers on diagnostic chart.

1. Checks to see if ECM recognizes a problem, and sets Code EO41.
2. This step verifies proper operation of circuits No. 633, 644 or 645.
3. Step validates integrity of circuit No. 630 from ignition module to ECM.
4. If camshaft gear magnet is interfacing with cam sensor, voltage reading will be zero. Bumping engine will cause condition to go away.
5. If voltage reading of terminal "BC5" is constantly varying and connection to terminal "BC5" is okay, ECM is at fault.

Check for the following conditions

1. Poor Connection or Damaged Harness. Inspect ECM harness connectors for backed out terminal "BC5", improper mating, broken locks, improperly formed or damaged terminals, poor terminal to wire connection and damaged harness.
2. Intermittent Test. If connections and harness check okay, monitor a digital voltmeter connected from ECM terminal "BC5" to ground while moving related connectors and wiring harness. If failure is induced, voltage reading will change. This may help to isolate the location of the malfunction.

Code EO41, Flow Chart - CAM Sensor Signal. Scheme 635

Code EO42, Schematic - EST Ignition Ckt. Scheme 636

The C(3)I module sends a reference signal to the ECM when the engine is cranking. When the engine is running less than 400 RPM, the C(3)I module controls ignition timing. When the engine speed exceeds 400 RPM, the ECM sends a 5 volt signal on by-pass circuit No. 424 to switch timing to ECM control. An open or ground in the EST circuit will stall the engine and set a Code EO42. The engine can be restarted but will run on module timing. The following conditions must be met to set a Code EO42

1. Engine speed greater than 600 RPM with no EST pulse for 200 milliseconds (open or grounded circuit No. 423).
2. ECM commanding by-pass mode (open or grounded circuit No. 424).

Note. Test numbers refer to test numbers on diagnostic chart.

1. Checks to see if ECM recognizes a problem. If it does not set Code EO42, it is an intermittent problem and could be due to a loose connection.
2. With ECM disconnected, ohmmeter should be reading less than 200 ohms, which is the normal resistance of EST circuit through C(3)I module. A higher resistance would indicate a fault in circuit No. 423, poor C(3)I module connection, or faulty C(3)I module.
3. If test light was on when connected from 12 volts to ECM harness terminal "BC7", either circuit No. 424 is shorted to ground or C(3)I module is faulty.
4. Checks to see if ignition module switches when by-pass circuit is energized by 12 volts through test light. If ignition module actually switches, ohmmeter reading should shift to greater than 6000 ohms.
5. Unplugging ignition module should cause ohmmeter to read as if it were monitoring an open circuit (infinite reading). If not, circuit No. 423 is shorted to ground.

An intermittent may be caused by a poor connection, rubbed through wire insulation, or a wire broken inside the insulation. Check for the following conditions

1. Poor Connection or Damaged Harness. Inspect ECM harness connectors for backed out terminals "BC7" or "BC8", improper mating, broken locks, improperly formed or damaged terminals, poor terminal to wire connection and damaged harness.
2. Intermittent Test. If connections and harness check okay, connect digital voltmeter from affected terminal to ground and move related connectors and wiring harness. If failure is induced, voltage reading will change.

Code EO42, Flow Chart - EST Ignition Ckt. Scheme 637

Code EO43, Schematic - ESC Ckt. Scheme 638

The knock sensor is used to detect engine detonation. The ECM will retard electronic spark timing based on the signal being received. The circuitry within the knock sensor causes the ECM's supplied 5-volt signal to be pulled down, so that under a no knock condition, circuit No. 496 would measure about 2.5 volts. The knock sensor produces an AC signal which rides on the 2.5 volts (DC voltage). The amplitude and signal frequency are dependent upon the knock level.

If circuit No. 496 becomes open or shorted to ground, voltage will either go greater than 3.5 volts or less than 1.5 volts. If either of these conditions are met for about 5 seconds, a Code EO43 will stored.

Note. Test numbers refer to test numbers on diagnostic chart.

1. Code EO43 will set if: Voltage on circuit No. 496 goes greater than 3.5 volts or less than 1.5 volts. All of above conditions met for 5 seconds. If an audible knock is heard from the engine, repair internal engine problem, normally no knock should be detected at idle.
2. If tapping on engine lift hook does not produce a knock signal, try tapping engine closer to sensor before proceeding.
3. The ECM has a 5-volt pull-up resistor which should be present at knock sensor terminal.
4. This test determines if knock sensor is faulty or if ESC portion of the MEM-CAL is faulty.

Code EO44, Schematic - O2 Sensor Ckt (Lean Exhaust Indicated). Scheme 639

Note. Test numbers refer to test numbers on diagnostic chart.

1. Running the engine at 1000 RPM keeps O2 sensor hot, so an accurate display voltage is maintained.
2. Opening O2 sensor wire should result in a voltage display of between 350 and 550 mV. If display is still fixed less than 350 mV, fault is a short to ground in circuit No. 412 or ECM is faulty.

Using ED20 display, observe the block learn values at different RPM and airflow conditions. If the conditions for Code EO44 exists, the block learn values will be around 150. Check for the following conditions

1. Oxygen sensor pigtail may be mispositioned and contacting exhaust manifold.
2. Check for intermittent ground in wire between connector and sensor.
3. A Mass Airflow (MAF) sensor output that causes ECM to sense a lower than normal airflow will cause the system to go lean. Disconnect MAF sensor and if lean condition is eliminated, replace MAF sensor.
4. Perform injector balance test, see CHART C2A.
5. Water, even in small amounts, near in-tank fuel pump inlet can be delivered to injectors. Water causes a lean exhaust and can set Code EO44.
6. System will be lean if pressure is too low. It may be necessary to monitor fuel pressure while driving vehicle at various road speeds and/or loads to confirm problem. See CHART A7.
7. If there is an exhaust leak, engine can cause outside air to be pulled into exhaust, across the oxygen sensor. Vacuum or crankcase leaks can cause a lean condition.
8. If all of the above checks are okay, replace oxygen sensor.

Code EO44, Flow Chart - O2 Sensor Ck (Lean Exhaust Indicated). Scheme 640

Code EO45, Schematic - O2 Sensor Ckt (Rich Exhaust Indicated). Scheme 641

Using ED20 display, observe the block learn values at different RPM and airflow conditions. If the conditions for Code EO45 exists, the block learn values will be around 115. Check for the following conditions

1. Fuel Pressure. System will go rich if pressure is too high. ECM can compensate for some increase in fuel pressure. If fuel pressure becomes too high, a Code EO45 may be set. See fuel system diagnosis in CHART A7.
2. Rich Injector. Perform injector balance test, see CHART C2A.
3. Leaking Injector. See CHART A7 for diagnosis.
4. Canister Purge. Check for fuel saturation. If full of fuel, check canister control and hoses. See CHART C3 for diagnosis.
5. MAF Sensor. An output that causes ECM to sense a higher than normal air flow can cause system to go rich. Unplugging MAF sensor will allow ECM to set a fixed value for sensor. Substitute a different MAF sensor if rich condition is rectified while sensor is unplugged.
6. Fuel. Check for leaking fuel pressure regulator diaphragm by checking vacuum line to regulator for raw fuel. Check for contaminated fuel.
7. TPS. An intermittent TPS output will cause system to go rich, due to a false indication of engine acceleration.
8. EGR. An EGR staying open (especially at idle) will cause the O2 sensor to indicate a rich exhaust, and could result in a Code EO45.

Code EO45, Flow Chart - O2 Sensor Ckt (Rich Exhaust Indicated). Scheme 642

Code EO46, Schematic - PSPS Ckt. Scheme 643

To set a Code EO46, the following conditions must be met

1. Closed power steering switch. E178 indicates "LO" (low voltage potential).
2. Vehicle speed is greater than 40 MPH.
3. Both conditions existing for a time greater than 25 seconds.

Note. Test numbers refer to test numbers on diagnostic chart.

1. Tests the power steering pressure switch for proper operation by using the self-diagnostic sytem. "LO" should be displayed when high power steering pressure loads are created.
2. This step determines whether the fault is in the switch or the circuit. A jumpered switch connector should normally indicate "HI" if the circuit is complete. If so, the power steering pressure switch or connection is faulty.
3. If display switches to "HI" when circuit No. 495 is grounded, the fault is an open in circuit No. 450.

An intermittent may be caused by a poor connection, rubbed through wire insulation, or a wire broken inside the insulation. Check for the following conditions

1. Poor Connection or Damaged Harness. Inspect ECM harness connectors for backed out terminal "BD4", improper mating, broken locks, improperly formed or damaged terminals, poor terminal to wire connection and damaged harness.
2. Intermittent Test. If connections and harness check okay, monitor EI78 display, while moving related connectors and wiring harness. If failure is induced, reading will change. This will help to isolate location of the malfunction.

Code EO46, Flow Chart - PSPS Ckt. Scheme 644

CODE EO47, ECM-BCM DATA

Check for momentary loss of BCM's 7 volts (circuit No. 807), ignition No. 3 (circuit No. 750) and PROM. See appropriate BCM charts.

If Code EO47 is set along with any of the following codes set as "HISTORY", B334, B335, B336, B337, B552 and B553, see chart on multiple intermittent codes.

CODE EO48, MISFIRE DIAGNOSIS

Code EO48 will set if following conditions are met

1. TPS is between .48 and 1.30 volts.
2. RPM is between 1300 and 2100.
3. MPH is between 50 and 60.
4. Oxygen sensor cross counts are greater than 21.
5. All of the above for 30 seconds.

Code EO48 will set when a problem exists with electrical system, fuel system or a basic engine problem, such as

1. A fuel related problem (such as restricted fuel injector).
2. A problem with ignition system such as bad plug wires, spark plugs or coil pack.
3. Check for other engine related problems such as burned or worn valves, weak valve springs, poor compression, worn camshaft or faulty lifters.

For more items to check, see CCC EFI TESTS W/O CODES

Code EO48, Flow Chart - Misfire Diagnosis. Scheme 645

CODE EO51, MEM-CAL ERROR

Checks that all pins are fully inserted in socket. If okay, replace PROM, clear memory and recheck. If Code EO51 reappears, replace ECM.

CODE EO63, EO64 & EO65, Schematic - EGR Flow Check. Scheme 646

Codes EO63, EO64 and EO65 are EGR flow test failures. The ECM, on a closed throttle coast down, will cycle solenoids on and off individually and look for a consequent change in engine RPM and O2 sensor activity.

1. If a code is set, inspect EGR for damage. Start and idle engine. Enter ECM overrides ES02, ES03 and ES04. You should be able to discern a change in engine RPM as the ECM turns on the EGR. Override ES02 should result in a small change and ES04 in a large change in RPM. The engine may stall when ES04 is turned on.

Note. If digital EGR valve shows signs of excessive heat, possibly slightly melted, check exhaust system for blockage (possibly a plugged converter) using procedure found in CHART B1. If exhaust system is restricted, repair cause, one of which is open due to grounded driver circuit, stuck injector or faulty ECM. If this condition is found, oil should be checked for possible fuel contamination.

CODE EO63, EO64 & EO65, Flow Chart - EGR Flow Check. Scheme 647

"Driver Door Ajar" Message - Schematic. Scheme 648

BCM supplies and monitors voltage on Circuit No. 3C12. If voltage is sensed as being low (door ajar), BCM will display "Driver Door Ajar" message under the following conditions

1. PRNDDL is okay.
2. Engine is running.
3. Transmission not in Park or Neutral.
4. Driver door ajar switch input is low.

Or if the following conditions exist

1. "Driver Door Ajar" failure code already set.
2. Driver door ajar switch is closed.

If system is to be tested, ensure that Code B334 is not set (ECM UART data line is okay).

"Passenger Door Ajar" Message - Schematic. Scheme 649

BCM supplies and monitors voltage on circuit No. 3C14. If voltage is sensed as being low (door ajar), BCM will display "Driver Door Ajar" message under the following conditions

1. PRNDDL is okay.
2. Engine is running.
3. Transmission not in Park or Neutral.
4. Driver door ajar switch input is low.

Or if the following conditions exist

1. "Driver Door Ajar" message already set.
2. Driver door ajar switch is closed.

If system is to be tested, ensure that Code B334 is not set (ECM UART data line is okay).

"Seat Belt" Telltale & Chime - Schematic. Scheme 650

BCM supplies and monitors voltage on circuit No. 3C15. If voltage is sensed as being low (seat belt unbuckled), BCM will display "Seat Belt" message under the following conditions

1. Engine is running.
2. Seat belt unbuckled.
3. Engine running time less than 6 seconds.

"Headlights Are On" Chime - Schematic. Scheme 651

BCM monitors terminal No. 2B7. When parking light switch is closed, oltage is sensed by BCM through circuit No. 308. When parking light switch is open, zero voltage will be sensed by the BCM. BCM will display "Headlamps Are On" message under the following conditions

1. Parking light switch is on.
2. Key not in ignition.
3. Driver door is open.
4. Ignition is off.

"Low Oil Pressure" Message & Telltale - Schematic. Scheme 652

Oil pressure sensor is a variable resistor the changes resistance proportional to oil pressure. BCM monitors resistance at terminal No. 3D9. If oil pressure drops to less than 6 psi, BCM will illuminate "Low Oil Pressure" message. This will occur after engine has been running for at least 5 seconds and if the following conditions exist

1. Oil pressure is less than 6 psi.
2. Engine speed greater than 600 RPM.
3. Above failure conditions present for a predetermined time.

Or if the following conditions exist

1. Code B334 is set.
2. Oil pressure is less than 6 psi.

"Oil Level Is Low" Message - Schematic. Scheme 653

The BCM supplies and monitors voltage at terminal No. 1D1. When oil level switch is closed (normal oil level), BCM will sense low voltage. If oil level switch is open (low oil level), BCM will sense high voltage and illuminate "Oil Level Is Low" message. This will occur under the following conditions

1. No Code B334.
2. Coolant sensor operating properly.
3. Coolant temperature drop since last ignition cycle, greater than predetermined degrees.

"Fuel Level Is Low" Message - Schematic. Scheme 654

The BCM monitors the fuel level sender in the fuel tank at terminal No. 2B8. If the average calculated fuel is 1.9 gallons or less, the "Fuel Level Is Low" (or lowest bar of fuel gauge will flash) message will be illuminated.

"Washer Fluid Is Low" Message - Schematic. Scheme 655

The BCM supplies and monitors voltage at terminal No. 2A4. When fluid level circuit is open, BCM will sense high voltage. When fluid level circuit is closed (low washer fluid), BCM will sense low voltage and illuminate "Washer Fluid Is Low" message. BCM will illuminate message if low washer fluid exist for at least 15 seconds.

"Overspeed Alarm" Message - Schematic. Scheme 656

The overspeed alarm is an operator-control vehicle speed warning designed to alert driver that vehicle speed has exceeded set point. The "Overspeed Alarm" message will appear when vehicle speeds set point and disappear if overspeed alrm is reset or vehicle speed drops to less than set point. Diagnosis of vehicle speed sensor may be required. BCM will display message if the following conditions exist

1. Code B124 not set current.
2. Overspeed set point not zero MPH.
3. Vehicle speed greater than overspeed set point.

"Key In Ignition" Warning Chime - Schematic. Scheme 657

The BCM supplies and monitors voltage at terminal No. 3C13. When ignition switch circuit is closed (ignition key in lock position) voltage is pulled low, BCM will display "Key In Ignition" message under the following conditions

1. Key in ignition.
2. Driver door is open.
3. Ignition is off.

Flashing Coolant Gauge Schematic - "Hot" Telltale, "Engine Overheat" Message & Fast Chime. Scheme 658

The ECM supplies and monitors voltage from coolant temperature sensor circuit at terminal No. 3D4. BCM will check the ECM (through UART data line circuit No. 800) every one second. If the calculated coolant temperature reaches 126°C and other failure conditions are met, BCM will display message. The following are failure conditions that BCM must see to display message

1. Engine coolant temperature greater than 126°C.

Or the following conditions.

1. Engine overheat condition already present.
2. Engine coolant temperature greater than 120°C.

Diagnosis of coolant temperature sensor and/or circuit may be necessary.

"Park Brake On" Message - Schematic. Scheme 659

The BCM supplies and monitors voltage from parking brake switch at terminal No. 1C5. When parking brake is pulled, switch is closed (grounded). BCM senses voltage being pulled low and illuminates "Park Brake On" message. BCM will display message under the following failure conditions

1. Park brake is applied (switch is closed).
2. Ignition is on.
3. Transmission not in Park or Neutral.

"Brake Fluid Is Low" Message - Schematic. Scheme 660

The BCM supplies and monitors voltage from brake fluid level switch at terminal No. 1C2. When brake fluid level is low (switch closed), BCM senses voltage being pulled low, and will illuminate "Brake Fluid Is Low" message if condition exists for at least 5 seconds. On vehicles without ABS, a brake fluid pressure switch is also used and functions the same as brake fluid level switch.

Antilock Telltale On - Schematic. Scheme 661

If this telltale is activated check brake fluid level. If brake fluid level is okay, ABS system requires diagnosis. For complete diagnosis and testing, see appropriate ABS article in BRAKES section.

WIRING DIAGRAMS

See also:
• CCC EFI TESTS W/O CODES