Dfi ECM Tests W/codes Cadillac Eldorado IX

ENTERING DIAGNOSTIC MODE - TESTING

Turn ignition switch to "ON" position. Press "OFF" and "WARMER" buttons on climate control panel simultaneously, and hold until segment check is displayed on the instrument panel and the Climate Control/Driver Information Center (CCDIC). (Scheme 128)

Note. Operating vehicle in the diagnostic mode for extended time periods (1/2 hour or longer), without the engine running, will cause battery drain, and possibly relate false diagnostic information and/or a no-start condition.

DFI/ECM System Control Schematic. Scheme 127

Climate Control/Driver Information Center (CCDIC). Scheme 128

SEGMENT CHECK

The segment check illuminates the Instrument Panel Cluster (IPC) and CCDIC to ensure that all segments of the vacuum fluorescent displays are working. The turn signal indicators do not light during this check. If all segments are not lit, diagnosis should NOT be attempted, as misdiagnosis may occur (code "E034" appears as "E031", etc.). If any portions or segments of the CCDIC display are inoperative, it must be replaced.

TROUBLE CODE DISPLAY

After diagnostic mode is entered, all trouble codes stored in memory will be displayed. All ECM codes are prefixed with an "E" (i.e. E013, E014, etc.). Lowest numbered ECM codes will be displayed first, followed by higher numbered codes. If no ECM codes are stored, a "NO ECM CODES" message will be displayed.

Following the highest numbered ECM code or the "NO ECM CODES" message , the BCM codes will be displayed. All BCM codes are prefixed with an "B" (i.e. B013, B014, etc.) and displayed in ascending order as with ECM codes. If no BCM codes are stored, a "NO BCM CODES" message will be displayed.

Any ECM or BCM will also be accompanied by the words "CURRENT" or "HISTORY". A "HISTORY" code indicates an intermittent failure, a "CURRENT" code indicates that fault still exists (current failure). If "LO" button on CCDIC is pressed, at any time DURING display of trouble codes, display of trouble codes will be by-passed.

SYSTEM SELECTION

Following trouble code display, the first available system selection level (i.e. "ECM?") will be displayed. (Scheme 129) While selecting a system to test, any of the following actions may be taken to control the display

1. Pressing "OFF" button on CCDIC panel will stop the system selection process and return display to beginning of trouble code sequence.
2. Pressing the "LOW" fan button will display the next available system selection. This allows display to be stepped through all system selections. The list of systems can be repeated following the end of system selection list.
3. Pressing the "HIGH" fan button will select the displayed system for testing.

System/Test Level Sequence Chart. Scheme 129

TEST TYPE SELECTION

Having selected a system, the first available test type (i.e. "ECM DATA?") will be displayed. (Scheme 129) When selecting a specific test type, the following actions may be taken to control display

1. Pressing "OFF" button on CCDIC panel will stop the test type selection process and return display to the next available system selection.
2. Pressing the "LOW" fan button will display the next available test type for the selected system. This allows display to be stepped through all available test types. The list of test types can be repeated following the display of the last test type.
3. Pressing the "HIGH" fan button will select the displayed test type. At this point the first of several specific tests will appear.

TEST CHOICE SELECTION

Selection of "DATA?", "INPUTS?", or "OVERRIDE?" test types will result in the first available test being displayed. (Scheme 129) If dashes ever appear, this test is not allowed with engine running.

Four characters of the display will contain a test code to identify the selection. The first 2 characters are letters which identify the system and the test type (i.e. ED for ECM data), last 2 characters numerically identify the test (i.e. ED01 for throttle position). When selecting a specific, the following actions may be taken to control the display

1. Pressing "OFF" button on CCDIC will stop the test selection process and return display to the next available test type for the selected system.
2. Pressing the "LOW" fan button will display the next smaller test number for the selected test type. If this button is touched with the lowest test number displayed, the highest test number will then appear.
3. Pressing the "HI" fan button will display the next larger test number for the selected test type. If this button is touched with the highest test number displayed, the lowest test number will then appear.

"CLEAR CODES?" SELECTION

Selecting the "CLEAR CODES?" test type will result in a "CLEAR CODES?" message display, along with the name of the system was being tested. This message will be displayed for 3 seconds to indicate that all stored trouble codes have been erased from system's memory. After 3 seconds, the display will automatically return to the next available test type for the selected system.

ECM "SNAPSHOT?" SELECTION

Selection of "SNAPSHOT?" test type while in the ECM system level will allow the recall of up to 3 snapshots recorded at the time the ECM malfunction codes were set. (Scheme 130) Also, one may trigger the recording of a snapshot upon demand. Pressing the "HI" button while in the ECM system level, will result in the display of "EXXX SNAPSHOT?". The "XXX" is the 3-digit diagnostic code that recorded the snapshot. While selecting snapshot, any of the following actions may be taken to control the display

1. Pressing "OFF" button on CCDIC panel will stop the test type selection process and return the display to the next available system selection.
2. Pressing the "LO" button will allow scrolling through the list of ECM diagnostic codes that the ECM has stored a snapshot for. Pressing the "LO" button will display the "TAKE ECM SNAPSHOT?" message and return system to the first "EXXX SNAPSHOT?" display.
3. Pressing the "HI" button with "SNAP DATA?" or "SNAP INPUTS?" displayed, will select that test type. At this point the display is controlled as it would be for non-snapshot data and input displays, however, all values and status information represents memorized vehicle conditions.

BCM "SNAPSHOT?" SELECTION

Selection of "SNAPSHOT?" test type while in the BCM system level will allow the recall of up to 3 snapshots recorded at the time the BCM malfunction codes were set. (Scheme 130) Also, one may trigger the recording of a snapshot upon demand. Pressing the "HI" button while in the BCM system level, will result in the display of "BXXX SNAPSHOT?". The "XXX" is the 3-digit diagnostic code that recorded the snapshot. While selecting snapshot, any of the following actions may be taken to control the display

1. Pressing "OFF" button on CCDIC panel will stop the test type selection process and return the display to the next available system selection.
2. Pressing the "LO" button will allow scrolling through the list of BCM diagnostic codes that the BCM has stored a snapshot for. After the last BCM diagnostic code, or the third if there are more than 3 codes set, pressing the "LO" button will display the "TAKE BCM SNAPSHOT?" message and return system to the first "BXXX SNAPSHOT?" display.
3. Pressing the "HI" button with "SNAP DATA?" or "SNAP INPUTS?" displayed, will select that test type. At this point the display is controlled as it would be for non-snapshot data and input displays, however, all values and status information represents memorized vehicle conditions.

EXITING DIAGNOSTIC MODE

Press "RESET/RECALL" button on CCDIC panel any time DURING display of trouble codes. (Scheme 128) Diagnostic mode will be ended and computerized engine control system will go back to normal operation.

Snapshot Test Level Sequence Chart. Scheme 130

ECM DATA DISPLAYS IDENTIFICATION

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

ECM "ED01" DATA CODE

The Throttle Position Sensor (TPS) position will be displayed in degrees.

ECM "ED02" DATA CODE

Manifold Air Pressure (MAP) sensor reading is displayed in Kilopascals (kPa).

ECM "ED03" DATA CODE

The computed barometric pressure will be displayed in Kilopascals (kPa).

ECM "ED04" DATA CODE

The coolant temperature is displayed in degrees Celsius (°C). (Scheme 131)

ECM "ED05" DATA CODE

Manifold Air Temperature (MAT) sensor reading is displayed in degrees Celsius (°C).

ECM "ED06" DATA CODE

Injector pulse width is displayed in milliseconds (ms).

ECM "ED07" DATA CODE

Oxygen sensor reading is displayed in volts.

ECM "ED08" DATA CODE

Spark advance is displayed in degrees. (Scheme 131)

ECM "ED10" DATA CODE

Battery state of charge is displayed in volts.

ECM "ED11" DATA CODE

Engine speed is displayed in RPM.

ECM "ED12" DATA CODE

Vehicle speed is displayed in MPH.

ECM "ED18" DATA CODE

Oxygen (O2) sensor cross-counts are displayed as the number of times the O2 sensor crossed reference line each second. (Scheme 131)

ECM "ED19" DATA CODE

Fuel integrator operation is displayed in counts.

ECM "ED26" DATA CODE

The transmission temperature will be displayed in degrees Celsius (°C).

ECM "ED70" DATA CODE

Cruise control servo operation is displayed in percent. A value close to "0" represents the at rest position. A value close to "100" represents wide open throttle.

ECM "ED98" DATA CODE

The ignition cycle counter value is the number of times the ignition key is cycled to the "OFF" position since an ECM trouble code was last detected. After 50 ignition cycles without any malfunction being detected, all stored ECM codes are cleared. (Scheme 131)

ECM "ED99" DATA CODE

The ECM Programmable Read-Only Memory (PROM) identification number is displayed as a number up to 3 digits long which can be used to verify that proper PROM is installed in ECM.

ECM Diagnostics/Basic Operation & Status Light Displays. Scheme 131

ECM Diagnostics/Data,Input,Output Tests/Fixed Spark Mode. Scheme 132

INPUT DISPLAYS

When trouble shooting a malfunction, the ECM input display can be used to determine if the 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 the input terminal voltage for that circuit.

The display also indicates if the input changed state (activated or deactivated) 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.

Input display may show Instrument Panel Cluster (IPC) trouble codes. The following is a brief summary of each ECM input.

ECM "EI71" INPUT CODE

The brake switch display is "LO" when brake pedal is depressed. (Scheme 132)

ECM "EI72" INPUT CODE

The throttle switch display is "HI" when accelerator pedal is depressed.

ECM "EI74" INPUT CODE

The park/neutral switch display is "LO" when vehicle is in Park or Neutral.

ECM "EI78" INPUT CODE

The power steering pressure switch display is "LO" when power steering pressure (effort) is high. (Scheme 132)

ECM "EI79" INPUT CODE

The cruise control "ON/OFF" switch display is "HI" when switch is in the "ON" position.

ECM "EI80" INPUT CODE

The cruise control "SET/COAST" switch display is "HI" when "ON/OFF" switch is in the "ON" position and the "SET/COAST" switch is depressed.

ECM "EI81" INPUT CODE

The cruise control "RESUME/ACCEL" switch display is "HI" when "ON/OFF" switch is in the "ON" position and the "RESUME/ACCEL" switch is pushed. (Scheme 132)

OUTPUT DISPLAYS

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

ECM "EO00" OUTPUT CODE

This test displays "CYCLE NONE" message as no outputs are activated at this point.

ECM "EO01" OUTPUT CODE

The canister purge solenoid display will be "LO" when solenoid is energized.

ECM "EO02" OUTPUT CODE

The Viscous Converter Clutch (VCC) display will be "LO" when VCC solenoid is energized.

ECM "EO03" OUTPUT CODE

The EGR solenoid display will be "LO" when solenoid is energized.

ECM "EO04" OUTPUT CODE

The AIR management system air switching solenoid display will be "LO" when solenoid is energized.

ECM "EO05" OUTPUT CODE

The AIR management system air diverter solenoid display will be "LO" when solenoid is energized.

ECM "EO06" OUTPUT CODE

The ISC motor display will be "LO" when plunger is retracting and "HI" during plunger extension.

ECM "EO07" OUTPUT CODE

The cruise control vent solenoid display is "HI" when vent solenoid is energized. The cruise control "ON/OFF" switch must be on and the engine off for this output to cycle.

ECM "EO08" OUTPUT CODE

The cruise control vacuum solenoid display is "HI" when vacuum solenoid is energized. The cruise control "ON/OFF" switch must be on and the engine off for this output to cycle.

ECM "EO09" OUTPUT CODE

The A/C relay display will be "HI" when relay is energized.

ECM "EO99" OUTPUT CODE

All of the previously mentioned outputs are cycled simultaneously. The "HI" and "LO" corresponds to status indications previously described.

OVERRIDE DISPLAYS

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

The display will alternate between "--" for one second, followed by the normal program value for 10 seconds. This alternating display is a reminder that function is not currently being overridden.

Pressing the "WARMER" or "COOLER" buttons on the CCDIC begins the override, at which time the display will no longer alternate to "--". When in override, pressing the "WARMER" button increases the value, while pressing the "COOLER" button decreases the value.

Upon release of button, the display may remain in either the override value or return to normal program control. If display remains at the override value, normal program control can be resumed in one of 3 different 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 opposite extreme. If the button is released while "--" is being displayed, normal program control will resume and the display will again alternate.

The override test type is unique in that any other test type within the selected system may be activated at the same time. After selecting an override test, pressing the "OFF" button will allow selection of another test type, yet the CCDIC will continue to display the selected override. By selecting another test type, while at the same time pressing the "WARMER" or "COOLER" buttons, it is possible to monitor the effect of the override on different vehicle parameters.

ECM "ES00" OVERRIDE CODE

This test will display a "NONE" message as no overrides are active at this point.

ECM "ES01" OVERRIDE CODE

The viscous converter clutch solenoid override can be activated by the "WARMER" or "COOLER" buttons. Its status is displayed as "ON/OFF".

ECM "ES02" OVERRIDE CODE

The EGR solenoid override status is displayed as "ON/OFF". Due to use of a positive backpressure type EGR valve, this test will have no significance at idle.

ECM "ES03" OVERRIDE CODE

ISC motor override status is displayed as "UP/DN" (up/down).

ECM "ES04" OVERRIDE CODE

The cruise control servo override status is displayed as "UP/DN" (up/down).

FIXED SPARK MODE (SETTING IGNITION TIMING)

1. Initial base timing is set by jumpering pins "A" and "B" together at ALDL connector, while NOT in diagnostic mode. The ALDL connector is located near brake pedal, just below dash. (Scheme 133)
2. Set timing to specification shown on EMISSION CONTROL LABEL. Jumpering pins "A" and "B" together will cause a "SET TIMING" message to appear on CCDIC. This indicates that ECM is in set ignition timing mode.

View of ALDL Connector. Scheme 133

DFI PERFORMANCE FLOW CHART DEFINITIONS

DFI PERFORMANCE CHARTS

VISUAL INSPECTION

Note. All DFI diagnosis should begin with a thorough visual inspection. Visual inspection can often lead to the repair of a simple problem without the use of diagnostic charts.

Visual inspection should include

1. Checking vacuum hoses for damaged and proper routing.
2. Checking for proper ground connections (ground eyelets connected to ground points). Ensure star washers are installed (if equipped). The engine/DFI fuel system grounds are located as follows: ECM and ALDL connector ground is located on body ground stud, near battery. Fuel pump ground is located in front of engine, near starter. The oxygen sensor reference circuit is grounded on engine, at rear bank of cylinders, with a ground eyelet on power steering line retainer clip.
3. Checking for blown or missing fuses or relays, or installed in wrong locations.
4. Checking air cleaner for proper installation. Heat tube and vacuum tap must be connected. PVC hose from rocker arm cover must be installed.

DFI SYSTEM CHECK

The DFI SYSTEM CHECK is an organized approach for identifying a problem caused by DFI system. Driver comments normally fall into one of the following areas: steady "ENGINE CONTROL SYSTEM" light, driveability problems, engine won't start, or stalls after start.

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

1. If "ENGINE CONTROL SYSTEM" light comes on while cranking, then the ECM is getting battery power and ground.
2. If "ENGINE CONTROL SYSTEM" light is on with engine running, check for ECM codes. Diagnose codes before proceeding with DFI system check.
3. After codes are corrected, ability of DFI system to control fuel delivery to engine must be checked.
4. Check for proper closed/open loop operation.
5. If closed loop is achieved, fuel system has to be checked for rich, lean or proper fuel control. The DFI system has an integrator which monitors oxygen sensor rich/lean status and drives fuel system richer if oxygen sensor signal is lean, or drives the fuel system leaner if sensor signal is rich.

The integrator has a range of 88-160 counts. The integrator value will be 128 when ECM does not have to modify fuel rate to engine. The integrator will reset to 128, if fuel system is in acceleration, power enrichment, some deceleration or open loop modes. The integrator resets to 128 when oxygen sensor is not in control of fuel. If integrator sees an oxygen sensor that is lean most of the time, the integrator value will go higher to try and add more fuel to engine. If integrator sees an O2 sensor that is rich most of the time, integrator value will go lower to try and drive fuel system leaner.

In this test, operate engine at closed loop (1000-2000 RPM with steady throttle) to stabilize integrator reading of 88-160. In most cases, this will indicate that fuel delivery system is okay.

DFI System Check. Scheme 134

CHART A1 (1 OF 2)

The "ENGINE CONTROL SYSTEM" (ECS) light is powered through the 10-amp "IGN-1" fuse No. 18 in fuse block, and grounded by ECM pin "C1" to illuminate. The ECS light will check bulb with key on. Light is illuminated steadily during cranking and is illuminated whenever a trouble code with service message is set.

If a service trouble code is set, the ECM will send a service status to BCM via the data link. At the same time, ECM grounds pin "C1" to turn on ECS light.

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

1. If code EO18 is present, diagnose code EO18 before proceeding. The ECS light illuminates with engine cranking only if crank input is present to ECM.
2. If code B334 is current ("NO ECM DATA" is displayed), go to CHART A1 (2 OF 2) to check for loss of power or ground to ECM.
3. If "STOP ENGINE/OIL" light is displayed with key on/engine off, power to cluster lights is okay. Diagnose location of open ground circuit to ECS light or for blown ECS light bulb.
4. Starting at ECM, this branch of chart follows circuit No. 325, grounding circuit No. 325 as ECM would do to turn bulb on. If a ground at given point on circuit No. 325 brings ECS light on, circuit from grounded point to light is okay.

Flow Chart A1 Schematic, No "Engine Control System" Light. Scheme 135

Flow Chart A1 (1 of 2), No "Eng Control System" Light. Scheme 136

Flow Chart A1 (1 of 2), No "Eng Control System" Light. Scheme 137

CHART A1 CONTINUED (2 OF 2)

If "ENGINE CONTROL SYSTEM" (ECS) light is inoperative and code B334 is current, the ECM may not be powering up with key on, may not be receiving full time power from battery, or may be damaged due to electrical overload or water intrusion.

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

1. Check for switched ignition power to ECM.
2. Check for ground to ECM. Pin "A12" and pin "D1" are redundant grounds. If either ground is okay, ECM should be able to operate normally. If both grounds are open, ECM will not power up.
3. Check for full time memory voltage supply to ECM. Pin "C16" and "B1" are redundant power supplies to ECM. If either power supply is okay, ECM should be able to operate normally.
4. If power, grounds and connections are okay, be sure to perform CHART C1 - ECM REPLACEMENT CHECK before replacing ECM. The ECM may have been damaged by electrical overload due to a low resistance component.

Flow Chart A1 Schematic, No "Eng Cont Sys" Lt (Code B334 Current). Scheme 138

Flow Chart A1 (2 Of 2), No "Eng Cont Sys" Lt (Code B334 Current). Scheme 139

Flow Chart A1 (2 of 2), No "Eng Cont Sys" Lt (Code B334 Current). Scheme 140

CHART A2 - "ENG CONTROL SYSTEM" LIGHT ON (NO CODES PRESENT

The "ENGINE CONTROL SYSTEM" (ECS) light is powered through the 10-amp "IGN-1" fuse in fuse block, and grounded by ECM pin "C1" to illuminate. The ECS light will check bulb with key on. Light is illuminated steadily during cranking, and is illuminated whenever a trouble code with a service message is set.

If a service trouble code is set, ECM will send a service status to BCM via the data link. At the same time, ECM grounds pin "C1" to turn on ECS light.

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

1. Intermittent loose grounds or power connections can cause ECM to repeatedly power-up, power-down or to reset.
2. Check for bulb grounded by ECM through pin "C1" or through a circuit fault.
3. Remove and replace both ECM connectors and ensure that they are latched. Check MEM-CAL unit for proper orientation, bent pins, and full seating in socket. Substitute a known good MEM-CAL unit to see if unit is causing the light to flicker. If test MEM-CAL unit does not correct condition, replace ECM. Be sure to perform CHART C1 - ECM REPLACEMENT CHECK.

Flow Chart A2, "Eng Cont System" Light On (No Codes Present). Scheme 141

Flow Chart A2, "Engine Control System" Light On (No Codes Present). Scheme 142

CHART A3 - NO START OR STALL AFTER START

All internal combustion engines require spark, fuel, air, and proper timing to operate. The DFI system is no different. If battery is at proper charge level, first step should be to determine which of these elements is missing.

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

1. Check for codes stored and for proper "ENGINE CONTROL SYSTEM" (ECS) light operation. Repair stored codes and improper ECS light operation before proceeding with CHART A3.
2. Injectors should spray only when engine is cranking or running. Look for spray, drips or leaks with key on/engine off.
3. Check for both injectors to spray fuel while cranking engine.
4. If fuel is okay, then check for spark. Use Spark Tester (ST-125) to test for spark. A spark plug with a wide gap or allowing a plug wire to arc to ground, may not test HEI for sufficient output and may damage coil, cap, or rotor.
5. This step by-passes EST system. If vehicle will start and run with EST system disabled (by-pass open), the no start condition may be due to an EST system fault. If ECM has poor ground to engine, or if distributor has a poor ground connection to ECM, distributor may not be able to recognize EST pulses and the engine will stall as ECM tries to enable EST. The system uses EST to control spark timing.
6. If vehicle will not start, the fuel system must be checked next. Connect Fuel Pressure Gauge (J-25400-300) and observe fuel pressure while cranking. The gauge should be installed in fuel inlet line at service fitting. A fuel pressure reading of 9-12 psi during cranking indicates that fuel system is operating properly. Improper fuel pressure indicates a fuel problem. See CHART A4A - FUEL SYSTEM DIAGNOSIS. Having spark and fuel spray from both injectors at correct fuel pressure, all DFI functions for starting are operating normally. Thus the cause of no start condition is a mechanical problem (i.e. spark plugs, valves, valve timing, etc.).

Flow Chart A3 Schematic, No Start Or Stalls After Starting. Scheme 143

Flow Chart A3, No Start Or Stalls After Starting. Scheme 144

Flow Chart A3, No Start Or Stalls After Starting (1 Of 2). Scheme 145

Flow Chart A3, No Start Or Stalls After Starting (2 Of 2). Scheme 146

CHART A4A - FUEL SYSTEM DIAGNOSIS

The DFI system requires that fuel pressure be 9-12 psi and steady under all driving conditions. Fuel Pressure Gauge (J-29658/BT8205) should be attached to fuel line service fitting with a Schrader valve fitting from Gauge Set (J-34730-1). This set up will give the technician a more precise and more responsive reading.

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

1. Fuel pressure should be 9-12 psi and steady. If not, go to CHART A4B - FUEL PRESSURE OUT OF RANGE.
2. If fuel pressure drops (leaks down) with key off, either the fuel pressure regulator cannot hold pressure or the fuel pump check ball is not seating. This branch of trouble tree will determine which is causing the fuel pressure leakdown.

Flow Chart A4A Schematic, Fuel System Diagnosis. Scheme 147

Flow Chart A4A, Fuel System Diagnosis. Scheme 148

Flow Chart A4A, Fuel System Diagnosis. Scheme 149

CHART A4B - FUEL PRESSURE OUT OF RANGE

This procedure tests for fuel supply system problems that can cause incorrect fuel pressure or incorrect fuel pump operation.

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

1. Fuel system diagnosis should begin by determining if fuel pump is operating properly. Fuel Pressure Gauge (J-25400-300) should be installed at fuel line service fitting. Measure fuel pressure while cranking engine. If fuel pressure is 9-12 psi, go to CHART A4A - FUEL SYSTEM DIAGNOSIS. If necessary, Fuel Pressure Gauge (J-29658/BT8205) may be attached to service line fitting with Schrader valve fitting from Gauge Set (J-34730-1). This set up will give technician a more precise and more responsive reading.
2. If fuel pump relay or ECM were cause of low fuel pressure, there would be an ECM code EO20 set. This step is to check for voltage supply to fuel tank 5-way connector.
3. If voltage signal to fuel tank connector is okay, an open may exist between 5-way fuel tank connector and fuel pump. If fuel pump runs with an alternate power source connected, the fuel tank unit is okay. Check throttle body fuel metering assembly for cause of low fuel pressure.
4. Check for fuel supply system (tank, filter, pump, sender, lines) ability to deliver at least 9 psi pressure or for throttle body fuel pressure regulator fault.
5. If fuel pressure is low with fuel return line plugged, throttle body fuel metering assembly is not at fault. A restriction or blockage may exist in fuel supply system. The fuel supply line should be checked visually for kinks and damage. The fuel filter element can also restrict flow. Check for proper fuel line routing, sender tubes for restrictions, check rubber between fuel pump and sending unit for leaks or restrictions, or collapsed fuel strainer in tank. If all of the above are okay, replace fuel pump.
6. Fuel pressure above 12 psi is caused either by a malfunction of pressure regulator or by a restriction in fuel return line. It should be noted that a secondary condition of spark plug fouling, code EO45 or oxygen sensor contamination resulting in code EO13 accompanied by code EO45, may result from too rich fuel flow. To isolate cause of high fuel pressure, disconnect return line at throttle body. Connect a fitting to throttle body which will accept a length of flexible rubber fuel hose. Insert other end of hose into a container and observe fuel pressure as ignition is tuned on. If fuel pressure remains above 12 psi, replace fuel metering assembly. If fuel pressure drops into 9-12 psi range, with fuel return line by-passed, the fuel return line is restricted. A restricted fuel return line can be diagnosed by visually inspecting line for kinks or damage. A kink in the Teflon fuel line (braided stainless steel clad) may not be visually obvious.
7. If fuel pump will not run with externally applied power, fault is an open circuit in fuel sending unit wiring to pump, or an open circuit at RFI suppression connector inside tank, or faulty fuel pump. The fuel sending unit must be removed from vehicle to check.

Flow Chart A4B, Fuel Pressure Out Of Range. Scheme 150

Flow Chart A4B, Fuel Pressure Out Of Range (1 Of 2). Scheme 151

Flow Chart A4B, Fuel Pressure Out Of Range (2 Of 2). Scheme 152

CHART A5 (1 OF 2)

The fuel injectors are powered through the 3-amp injector fuses. The ECM turns on injectors by applying a ground to ECM connector pins "D15" and "D16" (injector drive circuits). The ECM grounds injector drive circuits to turn on fuel injector to supply fuel to engine. ECM data parameter ED06 (injector pulse width), reflects time in milliseconds that ECM turns on ground to injectors for each injector pulse.

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

1. If this procedure is being followed for a no start condition, crank engine for 5 seconds to check distributor reference signal. If code EO12 does not set, turn ignition off for 10 seconds. Observe injectors as ignition is turned back on. If there is no spray, injectors are not stuck open. Observe injectors while cranking engine.
2. To determine if injector is being activated electrically, repeat procedure listed in step 1) with electrical connector removed. If injector continues to spray, injector is defective and must be replaced. If injector no longer sprays, drive circuit of the affected injector must be shorted to ground or ECM is grounding internally.
3. If both injectors spray or if neither injector sprays, it must be determined if the fuel system is operating properly. Fuel Pressure Gauge (J-25400-300) should be installed at fuel line service fitting. Measure fuel pressure while cranking engine. If fuel pressure is not 9-12 psi, go to CHART A4A - FUEL SYSTEM DIAGNOSIS.
4. If fuel pressure is between 9-12 psi and there was no spray from either injector while cranking, the injector circuit must be checked for proper voltage. If there is voltage at injector fuses, then the ECM must be faulty because it is not grounding both injector circuits. If there is no voltage at fuse, check for voltage at 10-amp ECM fuse which feeds the injector fuses. If there is voltage here, then an open circuit must exist between fuses and circuit No. 439. If there is no voltage at ECM fuse, then circuit No. 3 must be repaired for an open or short to ground.
5. If fuel pressure is between 9-12 psi and there was fuel spray from both injectors while cranking engine, check fuel system to determine if injectors leak. To check for injector leakage, start and run engine for 10 seconds. Turn engine off for at least 10 seconds. Turn ignition on to pressurize injectors. Visually check for dripping fuel from bottom of injectors. If fuel is dripping, check for damaged "O" rings. If "O" rings are okay, replace injector(s). If fuel does not drip, fuel system is okay.
6. If there is spray from only one injector, then there is a malfunction in the injector assembly or in the signal to the injector assembly. Malfunction can be isolated by switching injector connectors. If problem remains with the original injector after switching connector, the injector is defective and must be replaced.

Flow Chart A5 Schematic, Injector System Diagnosis. Scheme 153

Flow Chart A5, Injector System Diagnosis (1 of 2). Scheme 154

Flow Chart A5, Injector System Diagnosis (1 Of 2). Scheme 155

Flow Chart A5, Injector System Diagnosis (2 Of 2). Scheme 156

CHART A5 (2 OF 2)

Note. The injector circuit test should only be performed when driveability condition is present or when one injector is visually verified to be inoperative. For the injector circuit test to result in a positive diagnosis of an injector circuit fault, the voltage measurements requested by CHART A5 must be taken with injector fault present.

The fuel injectors are powered through the 3-amp injector fuses. The ECM turns on injectors by applying a ground to ECM connector pins "D15" and "D16" (injector drive circuits). The ECM grounds injector drive circuits to turn on fuel injectors to supply fuel to engine. ECM data parameter ED06 (injector pulse width), reflects the time in milliseconds that ECM turns on ground to injectors for each injector pulse.

When measuring voltages between ECM connector pins "D15" and "D16", the voltmeter should read "00.0" volts if ECM is able to control both fuel injectors to provide equal amounts of fuel. If one injector loses power from fuse or loses ground from ECM, the voltage measured between pins "D15" and "D16" will not be zero. This reflects unequal voltage drops across injector coils. The voltage reading obtained when an injector fault is present can be used to diagnose injector open to voltage, injector open to ECM, injector coil open, or ECM unable to ground injector drive circuits.

To get an accurate and useable voltage reading, Digital Volt/Ohm Meter (DVOM J34029-A) must be used. Connect the DVOM as directed by CHART A5 (Cont.) and must be set on 200-volt (DC) scale.

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

1. If DVOM reads "00.0" volts, both injectors are being powered through fuses and grounded by ECM an equal amount. No fault exists at this time.
2. If DVOM reads "00.2" or "02.0" volts and voltage polarity is negative, injector "B" is inoperative. Pin "D15" of Red ECM connector is not grounding injector drive circuit No. 468. The cause is an ECM connector fault or an ECM fault. If voltage polarity is positive, injector "A" is inoperative. Pin "D16" of Red ECM connector is not grounding injector drive circuit No. 467. The cause is an ECM connector fault or an ECM fault.
3. If DVOM reads above "2.0" volts, fault is an open circuit from one of the 3A injector fuses to ECM. A negative voltage polarity means that an open exists between injector "A" voltage supply and ECM. Check circuit No. 481, injector coil of injector connected to Blue and Red wires and circuit No. 467, for open or short circuits to ground. A positive voltage polarity means that an open exists between injector "B" voltage supply and ECM. Check circuit No. 482, injector coil of injector connected to Green and White wires, circuit No. 468 for open or short circuits to ground.

Flow Chart A5 (2 of 2), Injector System Diagnosis. Scheme 157

Flow Chart A5 (2 of 2), Injector System Diagnosis. Scheme 158

CHART A6 - OXYGEN SENSOR NOT READY

The ECM provides a .45-volt reference to oxygen sensor on circuit No. 412. When warm, a properly operating oxygen sensor will drive the .45-volt reference lower (below .45 volts) to indicate lean mixtures and higher (above .45 volts) to indicate a rich mixture.

When oxygen sensor is cold (below 200°C), the output voltage will be around 0.5 volts and the ECM will keep the system in open loop operation. When the ECM sees that the oxygen sensor is varying from cold voltage of .45 volts and engine coolant value is above 85°C, it will send the system into closed loop operation.

In closed loop operation, the ECM will adjust fuel delivery rate based upon oxygen sensor readings. CHART A6 should only be used when vehicle will NOT go into closed loop operation.

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

1. With key on and oxygen sensor disconnected, BCM data code ED07 should read .45 volts (nominal). Lower or higher voltage indicates circuit problems.
2. The ECM compares voltage on circuit No. 412 to ground voltage on circuit No. 413B. It's essential that the O2 sensor ground and the ECM ground show good continuity (no voltage difference with engine running).

Flow Chart A6 Schematic, Oxygen Sensor Not Ready. Scheme 159

Flow Chart A6, Oxygen Sensor Not Ready. Scheme 160

Flow Chart A6, Oxygen Sensor Not Ready (1 Of 2). Scheme 161

Flow Chart A6, Oxygen Sensor Not Ready (2 Of 2). Scheme 162

CHART A7 - LEAN EXHAUST SIGNAL

The ECM provides a .45-volt reference signal to oxygen sensor on circuit No. 412. When oxygen sensor is cold (below 200°C), the output voltage will be around .45 volts. The ECM will keep system in open loop operation. When warm, a properly operating O2 sensor will drive the .45-volt reference lower (below .45 volts) to indicate a lean mixture and higher (above .45 volts) to indicate a rich mixture.

The oxygen sensor signal voltage will swing from rich to lean rapidly (one swing every 2 seconds), if ECM is in control of air/fuel mixture. The low oxygen sensor voltage readings are normally evidence that the air-fuel mixture is lean and closed loop system is unable to compensate sufficiently due to a failure in some part of engine emission or fuel systems.

Less likely is the possibility that the oxygen sensor has failed and is giving an incorrectly low reading. However, if this is the case, closed loop fuel system will be overcompensating and causing rich operation while oxygen sensor is indicating lean readings.

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

1. If code EO13 is stored, DO NOT use this chart. See CHART A6 - OXYGEN SENSOR NOT READY.
2. With O2 sensor disconnected, reference voltage (.38-.63 volts) should appear. If ED07 reading is less than .38 volts, check for grounded signal circuit No. 412 or open ground circuit No. 413.
3. Check for ECM and oxygen sensor circuitry ability to record rich readings. The DVOM set on "VOLTS" scale will provide a few billionths of an amp to drive circuit No. 412 to above .64 volts (rich). Similar results may be obtained by placing one finger on battery positive terminal and another finger on oxygen sensor circuit No 412 harness terminal.
4. The ECM compares oxygen sensor signal voltage received on circuit No. 412 to ground voltage on circuit No. 413B. If the ECM does not have a good ground to engine on circuit No. 413B, oxygen sensor can appear falsely high or low. With engine running, use a voltmeter to measure voltage from oxygen sensor to pin "A1" at ECM. If voltage is -.05 volts to +.05 volts, ground circuit is okay. If voltage is less than -.05 volts or more than +.05 volts, repair poor ground connection between ECM pin "A1" and oxygen sensor ground eyelet on engine, at rear bank of cylinders, with a ground eyelet on power steering line retainer clip.
5. If oxygen sensor circuit is okay, lean exhaust is caused by fuel or emission systems not controlling the following: A fuel delivery system which is not functioning properly may cause a lean fuel mixture. This malfunction can be caused by fuel pressure less than 9 psi at injectors or by defective injectors. See CHART A4A - FUEL SYSTEM DIAGNOSIS. A loss of EGR will cause a lean fuel mixture. See CHART C6 - EGR DIAGNOSIS. If AIR management system were to send air to exhaust ports at all times, this would give a lean indication at oxygen sensor. See CHART C6 - AIR MANAGEMENT DIAGNOSIS. If CHART A9 - OXYGEN SENSOR DIAGNOSIS indicates that sensor is okay, check all connectors and terminals for an intermittent condition. Check for vacuum leaks at hoses, intake manifold and throttle body gaskets. Check for intermittent injector operation. See CHART A5 - INJECTOR SYSTEM DIAGNOSIS.

Flow Chart A7, Lean Exhaust Signal. Scheme 163

Flow Chart A7, Lean Exhaust Signal. Scheme 164

CHART A8 - RICH EXHAUST SIGNAL

The ECM provides a .45-volt reference signal to oxygen sensor on circuit No. 412. When oxygen sensor is cold (below 200°C), output voltage will be about 0.5 volts, the ECM will keep system in open loop operation. When warm, a properly operating oxygen sensor will drive the .45-volt reference lower (below .45 volts) to indicate a lean mixture and higher (above .45 volts) to indicate a rich mixture.

The oxygen sensor signal voltage will swing from rich to lean rapidly (one swing every 2 seconds), if ECM is in control of air/fuel mixture. Fixed high oxygen sensor voltage readings are normally evidence that air/fuel mixture is rich and closed loop system is unable to compensate sufficiently due to a failure in some part of engine emission or fuel systems.

Less likely is the possibility that the oxygen sensor has failed and is giving an incorrectly high reading. If the oxygen sensor is giving false rich readings, the closed loop fuel system will be overcompensating and causing lean operation while oxygen sensor is indicating rich.

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

1. If code EO13 is stored, DO NOT use this chart. See CHART A6 - OXYGEN SENSOR NOT READY.
2. With sensor disconnected, oxygen sensor reference voltage (.38-.63 volts) should appear. If ED07 reading is greater than .64 volts, check for circuit No. 412 shorted to voltage or poor ground on circuit No. 413B.
3. Check for oxygen sensor and ECM's ability to record lean readings.
4. The ECM compares oxygen sensor signal voltage received on circuit No. 412 to ground voltage on circuit No. 413B. If ECM does not have a good ground to engine on circuit No. 413B, oxygen sensor can appear falsely high or low. With engine running, use a voltmeter to measure voltage from oxygen sensor at exhaust manifold to pin "A1" at ECM. If voltage is -.05 volts to +.05 volts, the ground circuit is okay. If voltage is less than -.05 volts or more than +.05 volts, repair poor ground circuit connection between ECM pin "A1" and oxygen sensor ground eyelet on engine, at rear bank of cylinders, with a ground eyelet on power steering line retainer clip.
5. If oxygen sensor circuit is okay, rich exhaust is caused by fuel or emission systems not controlling the following: A restricted air cleaner could cause a rich fuel mixture. Inspect air cleaner and replace if necessary. A fuel delivery system which is not functioning properly may cause a rich fuel mixture. This malfunction can be caused by fuel pressure which is greater than 12 psi at injectors or by defective injectors. See CHART A4A - FUEL SYSTEM DIAGNOSIS. Excessive EGR flow displaces oxygen and causes a rich exhaust indication. See CHART A5 - INJECTION SYSTEM DIAGNOSIS. Injector dripping or injector leaks can cause rich exhaust. See CHART A5 - INJECTION SYSTEM DIAGNOSIS to check injectors. Fuel evaporation (carbon) canister loaded with fuel can cause rich operation. See CHART C3 - CANISTER PURGE DIAGNOSIS. Vacuum leak to MAP hose can cause a false high MAP reading. High MAP readings cause ECM to deliver too much fuel for current driving conditions. See code EO34 chart to diagnose. If CHART A9 - OXYGEN SENSOR DIAGNOSIS results indicate that the sensoris okay, check all connectors and terminals for an intermittent code.

Flow Chart A8, Rich Exhaust Signal. Scheme 165

Flow Chart A8, Rich Exhaust Signal. Scheme 166

CHART A9 - OXYGEN SENSOR DIAGNOSIS

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

1. With engine running warm (coolant temperature 185°F/85°C or greater) and at fast idle, observe engine data code ED07.
2. While running engine at fast idle, observe open/closed loop status light, and "AUTO" indicator light in CCDIC. If ECM switches system to closed loop operation, the oxygen sensor is okay. If ECM remains in open loop operation, coolant temperature code ED04 is above 185°F (85°C), and ECM and harness are operating properly as verified by CHART A6 - OXYGEN SENSOR NOT READY, replace oxygen sensor.
3. If voltage remains between .30-.60 volts for a minimum of one minute, check for the possibility of leaded or contaminated fuel before checking for a faulty oxygen sensor connection or a faulty oxygen sensor, as leaded fuel can damage catalytic converter and oxygen sensor.
4. If there is no voltage variation and if ECM and harness are operating properly as verified by CHART A6, check for faulty oxygen sensor.

Flow Chart A9, Oxygen Sensor Diagnosis. Scheme 167

Note. This chart assumes that "DFI System Check" and chart A-6 "Open Loop Diagnosis" have both been performed to verify that the ECM and oxygen sensor wiring are operating properly.

Flow Chart A9, Oxygen Sensor Diagnosis. Scheme 168

CHART C1 - ECM REPLACEMENT CHECK

Prior to replacing ECM, check for poor connector terminal to ECM contact. Check for a short circuit to battery voltage on an ECM ground circuit. Also check for shorted solenoids or relays. If a short is found, the circuit must be repaired BEFORE replacing ECM. This will prevent repeated ECM failures.

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

1. Check for poor terminal contact due to damaged or dirty ECM terminals. Remove suspected terminals to inspect, replace if damaged or dirty. If coolant is present at ECM connector, replace coolant temperature sensor, sensor connector, and sensor signal and ground wires. Also, replace ECM connector terminals and blow coolant out of harness. Clean ECM connector with alcohol and replace ECM.
2. This step check for a short circuit to ignition or for a shorted solenoid or relay. All terminals MUST be tested since several are connected together internally by ECM. A short in one circuit may cause another circuit in ECM to be inoperative. Any circuit testing below 20 ohms is shorted and should be diagnosed for cause of short.
3. Check ISC motor extend/retract circuits for short circuit to ground or shorted together. Normal resistance for an ISC motor circuit is 4-100 ohms.

Flow Chart C1, Connector Terminal ID, ECM Replacement Check. Scheme 169

Flow Chart C1, ECM Replacement Check. Scheme 170

Flow Chart C1, ECM Replacement Check (1 Of 2). Scheme 171

Flow Chart C1, ECM Replacement Check (2 Of 2). Scheme 172

CHART C3 - CANISTER PURGE DIAGNOSIS

The fuel vapor canister purge solenoid receives 12 volts from 10-amp fuse No. 5 in underhood relay panel through circuit No. 639. The ECM energizes the canister purge solenoid by grounding pin "A2" (circuit No. 428). When the solenoid is energized, it allows the canister to purge.

The canister is commanded to purge when closed loop has been reached, throttle switch is open, or when codes EO13, EO44, or EO45 are present. The ECM will de-energize the solenoid when code EO16 is set or the ECM is running in back-up mode (no normal program control).

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

1. Checks to see if canister purge solenoid is able to hold vacuum. If solenoid cannot hold vacuum, it must be replaced.
2. Vacuum should release when solenoid is cycled on when in output cycling mode.
3. Checks for proper vacuum signals from throttle body.
4. Checks for proper electrical signals to the canister purge solenoid.

FUNCTIONAL TEST OF FUEL VAPOR CANISTER

Attach hose to lower tube of Tank Pressure Control Valve (TPCV) on top of fuel vapor canister and attempt to blow through it. Little or no air should pass into canister.

Using a hand-held vacuum pump, apply 15 in. Hg of vacuum through TPCV upper tube. If canister does not hold vacuum for at least 20 seconds, diaphragm is leaking, replace fuel vapor canister.

If diaphragm holds vacuum, try to blow through hose connected to lower tube while vacuum is still applied. An increased flow of air should be observed. If not, replace fuel vapor canister.

Unplug canister purge solenoid connector, attach a hose to purge solenoid and attempt to blow through it. Air should not pass into canister. If air passes, replace canister purge solenoid. Measure resistance of canister purge solenoid. Resistance should be 20-200 ohms. If not, replace solenoid.

Flow Chart C3 Schematic, Canister Purge Diagnosis. Scheme 173

Flow Chart C3, Canister Purge Diagnosis. Scheme 174

Flow Chart C3, Canister Purge Diagnosis (1 Of 2). Scheme 175

Flow Chart C3, Canister Purge Diagnosis (2 Of 2). Scheme 176

CHART C4 - EST SYSTEM CHECK

The HEI distributor produces one 5-volt distributor reference pulse each time a cylinder reaches 10° BTDC (base ignition timing). These reference pulses are sent from distributor to ECM on circuit No. 430. ECM adds spark timing information to reference pulses received from HEI and sends out a 5-volt EST pulse over circuit No. 423.

The ECM can choose to control spark timing. The HEI by-pass circuit (circuit No. 424) is turned on by the ECM when the ECM wishes to control timing. The HEI by-pass circuit is turned off and the HEI module grounds EST circuit No. 423.

Circuit No. 453F is a common ground between ECM and HEI. The ECM and HEI compare by-pass, EST, and reference pulses to ground over this circuit. A circuit No. 453 open to the HEI or ECM can cause a failure of the ECM to recognize a reference pulse, or the HEI module to recognize an EST pulse.

The ECM compares status of EST circuit to the status of the by-pass circuit in order to detect a fault code E023. Possible causes for this code are: circuit No. 423 open or grounded. Circuit No. 424 open or grounded. Circuit No. 453F open to ground at HEI or ECM. Poor connections in circuit No. 450. ECM or HEI module faults.

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

1. Four 12" jumper wires must be obtained for use in diagnostic procedure. Jumper wires MUST have male and female Weatherpack Connectors (12014836 and 12014837) on either end. With distributor connector unplugged, use jumper wires to reconnect terminals. Use instructions provided in ECM CODE EO23 - EST CIRCUIT PROBLEM chart.
2. With only distributor reference and distributor reference ground jumpered, engine will run on back-up spark control. This step checks for proper ground connection between ECM and engine, and between ECM and HEI.
3. This step ensures that ECM is providing an EST output signal over circuit No. 423.
4. This step checks the ability of the HEI module to ground EST signal with an open by-pass circuit.

Flow Chart C4 Schematic, EST System Check. Scheme 177

Flow Chart C4 (1 Of 2), EST System Check. Scheme 178

Flow Chart C4, EST System Check (1 Of 2). Scheme 179

Flow Chart C4, EST System Check (2 Of 2). Scheme 180

1. 5) This step checks the ability if the HEI module to recognize a voltage on by-pass circuit and to stop grounding EST (ECM controlled timing).
2. 6) This step checks by-pass signal to HEI module. If by-pass signal is being sent by the ECM to the HEI, and if module is interpreting by-pass voltage correctly, then the module will switch off ground to EST.
3. 7) If chart leads to "EST CIRCUIT IS OKAY", then a fault may exist in the 4-pin weatherpack connector. Check connector and connector terminals. If connector is okay, clear codes and retest.

Flow Chart C4 (2 Of 2), EST System Check. Scheme 181

Flow Chart C4, EST System Check (1 Of 2). Scheme 182

Flow Chart C4, EST System Check (2 Of 2). Scheme 183

CHART C6 - AIR MANAGEMENT DIAGNOSIS

The air diverter and air switching solenoids are supplied with 12 volts on circuit No. 639 from 10-amp fuse No. 5 in underhood relay panel. The ECM controls AIR management system by grounding air switching solenoid circuit No. 436 and air diverter solenoid through circuit No. 429.

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

1. With engine cold, the AIR management system should switch air to exhaust ports to help oxidize the rich mixture that exists during cold starts and warm-up.
2. With engine warm, the air should be switched to catalytic converter to oxidize exhaust gases flowing into second stage of the converter.
3. Checks AIR management system's ability to divert air away from the catalytic converter during acceleration and deceleration.
4. Checks for vacuum supply to AIR management solenoids.
5. This step checks air pump operation.
6. This step checks ECM's ability to control air switching and air diverter solenoids.
7. This step checks for an open voltage circuit to solenoid.
8. This step checks for a low resistance solenoid. If resistance is less than 20 ohms, replace solenoid.

Flow Chart C6, Air Management Diagnosis. Scheme 184

Note. This procedure cannot be used if any of the following codes are current: EO13, EO16, EO23, EO31, EO32, EO34, EO44 or EO45.

Flow Chart C6, Air Management Diagnosis (1 Of 2). Scheme 185

Flow Chart C6, Air Management Diagnosis (2 Of 2). Scheme 186

CHART C7 - EGR DIAGNOSIS

Before entering diagnostic chart check 10-amp ECS fuse No. 5 of fuse block. Measure EGR resistance. Resistance should be 20-100 ohms. The DFI system use a positive backpressure type EGR valve which limits EGR flow with a low exhaust backpressure. Ensure that exhaust tubes which decrease backpressure (pull air through) are NOT hooked to vehicle when diagnosing EGR system.

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

1. Connect vacuum gauge to source side of EGR solenoid. Start engine and check for manifold vacuum. If manifold vacuum is not indicated, repair leaks or obstruction between the EGR solenoid and throttle body.
2. Connect vacuum gauge to EGR valve vacuum supply. There should be no vacuum with engine running. If there is, follow diagnostic chart.
3. With vacuum gauge connected to EGR valve vacuum supply, unplug the EGR solenoid connector. There should be more than 8 in. Hg of vacuum available. if not, repair leak or obstruction in EGR valve vacuum hose.

Flow Chart C7 (1 Of 2), EGR Diagnosis. Scheme 187

Flow Chart C7, EGR Diagnosis. Scheme 188

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

1. This step checks for voltage to EGR solenoid and ground signal from ECM. If either of these is missing, the EGR solenoid will command EGR to come on at all times.
2. This step checks ECM's ability to turn solenoid off. If light goes off, the electrical portion of the EGR system is okay.

DIAGNOSTIC AIDS

Check vacuum supply hoses for damage or obstructions. Clean out or replace as necessary. Check intake manifold passages for any obstructions that would prevent exhaust gases from passing through.

Flow Chart C7 (2 Of 2), EGR Diagnosis. Scheme 189

From Chart C-7 (1 Of 2). Scheme 190

CHART C8 - VCC DIAGNOSIS

The Viscous Converter Clutch (VCC) solenoid is turned on when the ECM applies ground to circuit No. 422. The power for the VCC solenoid comes from the 5-amp cruise control fuse in fuse block.

Current flows through VCC brake switch, into transmission VCC solenoid, and then into the transmission overtemp switch. The overtemp switch is normally closed and is opened when transmission sump temperature 315°F (157°C) is or greater.

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

1. This step checks continuity from brake switch through solenoid coil to circuit No. 422.
2. Checks for ECM to ground through circuit No. 420.
3. Checks for VCC to apply using the ECM override. If VCC does not apply, check transmission for hydraulic diagnosis of VCC.
4. The VCC electrical system is operating properly. Check transmission for hydraulic diagnosis of VCC.

Flow Chart C8 Schematic 1, VCC Diagnosis. Scheme 191

Flow Chart C8 (1 Of 2), VCC Diagnosis. Scheme 192

Flow Chart C8, VCC Diagnosis. Scheme 193

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

1. Checks for voltage coming from ignition switch to fuse.
2. If resistance measurement is infinity (open circuit), either overtemp switch, VCC solenoid, or related wiring inside transmission needs to be repaired.

Flow Chart C8 Schematic 2, VCC Diagnosis. Scheme 194

Flow Chart C8 (1 Of 2), VCC Diagnosis. Scheme 195

Flow Chart C8 (2 Of 2), VCC Diagnosis. Scheme 196

SELF-DIAGNOSTIC SYSTEM CHECK INFORMATION

The SELF-DIAGNOSTIC SYSTEM CHECK is an organized approach for identifying a problem caused by the on-car computer-controlled electronics. Understanding the chart and using it correctly reduces diagnostic time and prevents unnecessary replacement of parts.

The SELF-DIAGNOSTIC SYSTEM CHECK should be used to BEGIN DIAGNOSIS if any customer complaint which DOES NOT directly relate to a specific suBsystem.

If the "ENGINE CONTROL SYSTEM" light fails to illuminate during cranking, then the problem could be in the power supply circuit of the BCM/ECM computer system. The SELF-DIAGNOSTIC SYSTEM CHECK will direct technician to an appropriate diagnostic chart.

If the CCDIC display is not operating properly, BCM/ECM COMPUTER SYSTEM SELF-DIAGNOSTICS mode CANNOT be used. In this case, the SELF-DIAGNOSTIC SYSTEM CHECK will direct technician to an appropriate diagnostic chart.

If a trouble code is identified the BCM/ECM computer system self-diagnostics mode, problem can be corrected following the appropriate numbered code chart(s). If no code has been identified, the SELF-DIAGNOSTIC SYSTEM CHECK will direct technician to an appropriate diagnostic chart.

Flow Chart, Self-Diagnostic System Check. Scheme 197

Flow Chart, Self-Diagnostic System Check. Scheme 198

TROUBLE CODE/SYMPTOM IDENTIFICATION

ECM TROUBLE CODE IDENTIFICATION

ECM CHART A - MULTIPLE CODES STORED HARD

The conditions diagnosed by this chart, are caused by a single circuit failure, yet result in multiple diagnostic codes. If any of these conditions are met, follow the appropriate correction procedure before using the procedures for individual codes.

CHART A1

If codes EO22 and EO32 are both stored hard, the cause is probably a loss of 5 volts to circuit No. 474 (5 volt reference to MAP and TPS). To verify this condition, probe the following harness terminals with a voltmeter to ground: MAP sensor harness connector pin "C" and TPS connecter pin "C".

If voltage is zero for both circuits, check circuit No. 474 for an open or short to ground. If wiring is okay, either the ECM connector or the ECM itself is faulty. If 5 volt reference signal is available on both sensors' terminals, go to the diagnostic chart for each individual code. Diagnose code EO22 first and then code EO32.

CHART A2

If code EO15 is stored hard, along with code EO21 or EO26, the cause is probably an open in sensor ground circuit No. 476 for the coolant sensor and TPS. To verify, probe the following harness terminals with a voltmeter to 12 volts: coolant temperature sensor pin "A" (Black/Pink wire). TPS connector pin "B" (Black/Pink wire).

If voltage is zero at both sensors, check circuit No. 476A for an open. If wiring is okay, either the ECM connector or the ECM itself is faulty. If 12 volts is present at either of the sensor, follow the diagnostic chart for each individual code. Diagnose code EO15 first, code EO21 second, and code EO26 last.

CHART A3

If code EO31 is stored hard along hard codes EO38 and EO59, this condition is probably caused by an open in ground circuit No. 476A for the MAP, MAT and transmission temperature sensors. To verify this condition, probe the following harness terminals with a voltmeter to 12 volts: MAT sensor pin "A". MAP sensor harness pin "A". Transmission temperature sensor pin "A".

If voltage is zero at sensors, check circuit No. 476A for an open. If wiring is okay, either the ECM connector or the ECM itself is faulty. If 12 volts is present at sensors, follow the diagnostic chart for each individual code. Diagnose code EO31 first, code EO38 second, and code EO59 last.

Flow Chart A1 Schematic, Multiple Codes Stored Hard. Scheme 199

Flow Chart A1, Multiple Codes Stored Hard. Scheme 200

Flow Chart A1, Multiple Codes Stored Hard (1 Of 3). Scheme 201

Flow Chart A1, Multiple Codes Stored Hard (2 Of 3). Scheme 202

Flow Chart A1, Multiple Codes Stored Hard (3 Of 3). Scheme 203

ECM CODE EO12 - NO DISTRIBUTOR (TACH) SIGNAL

TEST CONDITIONS: Code EO12 is tested for during engine cranking operation (crank input to the ECM at system voltage).

FAILURE CONDITIONS: If ECM does not see distributor reference pulses for 2.1 seconds with crank input to ECM at system voltage, code EO12 will be set.

ACTION: ECM turns on "ENGINE CONTROL SYSTEM" light. ECM commands BCM to display "SERVICE NOW" message on CCDIC panel.

Possible causes of no distributor reference pulses are, open pick-up coil. HEI module unable to process pick-up coil signals. Open or shorts on circuit Nos. 430 and 453 from module 4-pin connector to ECM. Loss of 12 volts to "BAT" terminal of HEI.

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

1. This step checks for proper voltage of HEI system. If voltmeter shows .5-2.8 volts, HEI is producing reference pulses.
2. This step checks for proper ground connection between ECM and engine and also between ECM and HEI.
3. This step checks for proper voltage through circuit NO. 430BS from HEI to ECM. If ECM terminal "A7" sees .5-2.8 volts, then ECM is receiving reference pulses.
4. If HEI will produce spark, then fault is not within pick-up coil or module. Check circuit No. 430BS for opens or shorts to ground from module terminal "R" to pin "B" of 4-pin connector.

Notes On Intermittents

If code EO12 is stored as a history code, start engine and allow it to idle while manipulating circuit Nos. 430 and 453. An intermittent open will cause the engine to stumble or quit when ECM loses distributor reference.

If wiring and ECM connectors are okay, check HEI pick-up coil leads for intermittent open circuit.

Check for short to voltage on circuit No. 806, crank input to ECM pin "B3". If pin "B3" has voltage with key on and engine off, the ECM will record a false code EO12. If found, repair short to voltage on circuit No. 806.

Flow Chart, Code EO12, No Distributor (TACH) Signal. Scheme 204

Note. If engine will not crank, see "Starter Diagnosis".

Flow Chart, Code EO12, No Distributor (TACH) Signal (1 Of 2). Scheme 205

Flow Chart, Code EO12, No Distributor (TACH) Signal (2 Of 2). Scheme 206

ECM CODE EO13 - OXYGEN SENSOR NOT READY

If code EO13 is accompanied by current or history code EO45, diagnose code EO45 using chart. If code EO13 is accompanied by current or history code EO44, diagnose code EO44 using chart.

TEST CONDITIONS: Codes EO14, EO15, EO21, EO22, EO26 and EO27 are clear. Coolant temperature greater than or equal to 176°F (80°C). TPS value between 6 and 29 degrees. Throttle switch open. RPM greater than or equal to 800.

FAILURE CONDITIONS: Oxygen sensor voltage stays between .275 and .630 volts for more than 30 seconds (not toggling).

ACTION: ECM turns on "ENGINE CONTROL SYSTEM" light. ECM commands BCM to display "SERVICE SOON" message on CCDIC panel. ECM turns on canister purge and diverts AIR management air to air cleaner. Closed loop is disabled.

When warm, a properly operating oxygen sensor will drive the ECM's .45 volt reference signal lower (below .45 volts) to indicate a lean mixture, and higher (above .45 volts) to indicate a rich mixture. If under test conditions the oxygen sensor does not vary from the cold or not ready voltage, ECM assumes sensor can't respond to air/fuel mixture changes and sets a code EO13.

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

1. With key on and oxygen sensor disconnected, the parameter for ED07 should read about .45 volts. Lower or higher voltage indicates problems within the circuit.
2. The ECM compares voltage on circuit No. 412 to the ground voltage on circuit No. 413. It is essential that oxygen sensor ground and ECM ground on pin "A1" indicate good continuity (no voltage difference) with engine running.
3. Fault is most likely at ECM connector or ECM. See CHART C1 - ECM REPLACEMENT CHECK before replacing ECM.

If code EO13 is stored as a history code, start engine and enter diagnostics. Operate engine at fast idle until "AUTO" closed loop status light is turned on. Observe parameters of ED07 while manipulating wiring on circuit Nos. 412 and 413. If parameter ED07 changes from a fluctuating voltage to fixed .45 volts, repair intermittent open circuit.

Check circuit No. 413 for a good ground to engine (clean, tight star washer installed). Ground for circuit No. 413 is located on the engine, at right or rearmost cylinder head.

Review snapshot data parameters stored with this code to verify failure. If failure is verified, check and repair intermittent wiring connection or sensor.

Flow Chart, Code EO13, Oxygen Sensor Not Ready. Scheme 207

Note. If code EO13 is accompanied by hard or intermittent code EO44 or EO45, see DFI Chart A-6.

Flow Chart, Code EO13, Oxygen Sensor Not Ready. Scheme 208

ECM CODE EO14 - SHORTED COOLANT SENSOR CIRCUIT

TEST CONDITIONS: Codes EO37 and EO38 are clear. MAT sensor value less than or equal to 105°C.

FAILURE CONDITIONS: Coolant sensor value greater than or equal to 142°C (sensor signal shorted to ground).

ACTION: ECM turns on "ENGINE CONTROL SYSTEM" light. ECM commands BCM to display "SERVICE SOON" message on CCDIC panel. ECM turns off both AIR management solenoids. ECM uses MAT sensor value in place of coolant sensor value for all calculations.

The coolant sensor is a variable thermistor. The coolant sensor is a 2-wire sensor with a signal voltage coming from the ECM to sensor pin "B" (circuit No. 410PC), and a sensor reference ground on pin "A" (circuit No. 476PC).

As temperature of sensor increases, sensor resistance decreases. Signal voltage from ECM to pin "A" decreases as sensor temperature increases and current flows through sensor element to pin "A" (sensor ground). Code E014 sets because ECM assumes that coolant temperature can't be 142°C or greater when MAT is 105°C or less (sensor signal shorted to ground).

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

1. With coolant sensor shorted, parameter ED04 should read 142°C or more. If not, then sensor is not shorted. See NOTE ON INTERMITTENTS.
2. This step checks for a shorted coolant sensor or for a short in circuit No. 410. If parameter stays between 142-151°C with the sensor unplugged, then short is in circuit No. 410.
3. Fault is most likely at ECM connector or ECM. See CHART C1 - ECM REPLACEMENT CHECK before replacing ECM.

Manipulate wiring on circuit No. 410, coolant sensor, and ECM connector while observing ECM parameter ED04. If failure is induced, coolant temperature will jump from its normal value to the shorted reading of 142-151°C.

Disconnect and reconnect both the coolant sensor and ECM connectors, and ensure that they are properly latched. If wiring and connectors are okay, substitute and known good sensor and retest.

Review snapshot data parameters stored with this code to verify failure. If failure is verified, check and repair intermittent wiring connection or sensor.

Flow Chart, Code EO14, Shorted Coolant Sensor Circuit. Scheme 209

Flow Chart, Code EO14, Shorted Coolant Sensor. Scheme 210

ECM CODE EO15 - OPEN COOLANT SENSOR CIRCUIT

TEST CONDITIONS: Codes EO37 and EO38 clear. MAT sensor value greater than or equal to 5°C.

FAILURE CONDITIONS: Coolant sensor value is less than or equal to -35°C (sensor signal open).

ACTION: ECM turns on "ENGINE CONTROL SYSTEM" light. ECM commands BCM to display "SERVICE SOON" message on CCDIC panel. ECM turns off both AIR management solenoids. ECM uses MAT sensor value in place of coolant sensor value for all calculations.

The coolant sensor is a variable thermistor. The coolant sensor is a 2-wire sensor with a signal voltage coming from the ECM to sensor pin "B" (circuit No. 410PC), and a sensor reference ground on pin "A" (circuit No. 476PC).

As temperature of sensor decreases, sensor resistance increases. Signal voltage from ECM to pin "B" increases as sensor temperature decreases and less current flows through sensor element to pin "A" (sensor ground). Code E015 sets because ECM assumes that coolant temperature can't be -35°C or less when MAT is 5°C or greater (sensor signal open to sensor).

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

1. If sensor is open, parameter ED04 should read -35°C or less. If not, sensor signal is not open. See NOTE ON INTERMITTENTS.
2. This step checks for open sensor signal in circuit No. 410 from ECM to sensor connector. If parameter ED04 reads 148-151°C with connector shorted, then circuit No. 410 is okay.
3. This step checks for open sensor ground (circuit No. 476) from ECM to sensor. If pin "B" to ground causes parameter ED04 to read 148-151°C, then there is an open in circuit No. 476 between sensor pin "A" and ECM terminal "D13".
4. This step checks the ECM's ability to recognize a short to ground or low voltage on pin "B8", coolant signal.
5. Fault is most likely at ECM connector or ECM. See CHART C1 - ECM REPLACEMENT CHECK before replacing ECM.

Manipulate wiring on circuit Nos. 410PC and 476PC, coolant sensor, and ECM connector while observing ECM parameter ED04. If failure is induced, coolant temperature will jump from its normal value to the open reading of -35°C or less.

Disconnect and reconnect both the coolant sensor and ECM connectors, and ensure that they are properly latched. If wiring and connectors are okay, substitute and known good sensor and retest.

Review snapshot data parameters stored with this code to verify failure. If failure is verified, check and repair intermittent wiring connection or sensor.

Flow Chart, Code EO15, Open Coolant Sensor Circuit. Scheme 211

Flow Chart, Code EO15, Open Coolant Sensor Circuit. Scheme 212

ECM CODE EO16 - ALTERNATOR VOLTAGE OUT OF RANGE

TEST CONDITIONS: Code EO18 and EO20 clear. RPM greater than or equal to 800. No cranking signal (cranking input at ECM at zero volts).

FAILURE CONDITIONS: Voltage on fuel pump feedback to ECM less than 10 volts or more than 16 volts for 5 seconds or more.

ACTION: ECM turns on "ENGINE CONTROL SYSTEM" light. ECM commands BCM to display "SERVICE NOW" message on CCDIC panel. ECM turns off EGR solenoid, canister purge solenoid, and both AIR management solenoids. ECM disables cruise control. ECM disables VCC for entire key cycle.

The ECM monitors vehicle electrical system voltage or battery voltage indirectly by monitoring voltage on fuel pump feedback (circuit No. 120B).

Voltage readings taken by ECM are used to detect fuel pump voltage faults and to modify injector pulse width as system voltage varies. The ECM increases injector pulse width as system voltage decreases.

Code EO16 is set when The ECM sees low or high system voltage with an engine RPM high enough to allow full alternator output.

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

1. This steps checks alternator output at idle.
2. This step checks for insufficient alternator output with high electrical loads.
3. This step checks for high alternator output voltage.
4. This step checks for proper voltage at fuel pump test point (on fuel pump power circuit).
5. This step checks for an open circuit between ECM pin "D9" and fuel pump feed circuit.
6. If system voltage is out of limits, check charging system.

If history code EO16 is found, start engine, enter diagnostics, and display ECM parameter ED10. Manipulate wiring on circuit No. 120A form ECM pin "D9" to splice on circuit No. 120E. Observe if parameter drops to less than 10 volts. Many intermittent code EO16's can be traced to intermittent charging or battery system faults.

Check if "BATTERY NO CHARGE" light comes on. If BCM code B411 or B412 accompany history code EO16, also diagnose BCM codes B411 or B412. Check for low or overcharged battery.

Review snapshot data parameters stored with this code to verify failure. If failure is verified, check and repair intermittent wiring connection or sensor.

Flow Chart, Code EO16, Alternator Voltage Out Of Range. Scheme 213

Flow Chart, Code EO16, Alternator Voltage Out Of Range. Scheme 214

ECM CODE EO18 - OPEN CRANK SIGNAL CIRCUIT

TEST CONDITIONS: Engine RPM greater than or equal to 800.

FAILURE CONDITIONS: No crank signal has been received by the ECM since the last time that RPM was zero RPM (engine started, ECM didn't register a crank signal).

ACTION: ECM turns on "ENGINE CONTROL SYSTEM" light. ECM commands BCM to display "SERVICE SOON" message on CCDIC panel. Code is stored as current for entire key cycle.

The crank input signal to the ECM is an on/off signal that comes from the starter solenoid, through the 3-amp crank fuse, and then to pin "B3" of ECM. During crank, the signal is battery voltage, at all other times signal is zero volts.

Code EO18 is set if the ECM detects engine running at 800 RPM or more without having crank input go to system voltage.

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

1. DO NOT use this procedure if EO18 is a history code. See NOTE ON INTERMITTENTS.
2. If circuit No. 806 becomes grounded, the crank fuse will blow when engine is cranked.
3. This branch of diagnostic chart tests for ECM's or BCM's ability to short crank input signal to ground.
4. Voltage signal to crank fuse comes from ignition switch, through theft starter interrupt relay, and the park/neutral switch. This branch checks for opens between crank fuse and starter solenoid.

Remove crank fuse and check continuity on circuit No. 806 from crank fuse to ECM pin "B3". Check for intermittent opens while manipulating wiring.

If code EO18 doesn't set immediately after cranking, check for arcing at spark plug wires, loose engine grounds, or other sources of electromagnetic interference. Large transient voltage surges can erase crank signal from the ECM's memory and cause code EO18 to be set while driving.

Schematic, Code EO18, Open Crank Signal Circuit. Scheme 215

Flow Chart, Code EO18, Open Crank Signal Circuit. Scheme 216

Flow Chart, Code EO18, Open Crank Signal Circuit. Scheme 217

ECM CODE EO19 - SHORTED FUEL PUMP CIRCUIT

TEST CONDITIONS: Code EO18 clear. Engine RPM at zero. Crank input to ECM at zero volts (not cranking). Coolant light in bulb check (key on/engine off).

FAILURE CONDITIONS: Fuel pump feedback voltage greater than or equal to 11 volts for 3 seconds (fuel pump powered with engine not running).

ACTION: ECM turns on "ENGINE CONTROL SYSTEM" light. ECM commands BCM to display "SERVICE SOON" message on CCDIC panel.

The fuel pump receives power from circuit No. 120. Circuit No. 120 is fed by fuel pump relay and oil pressure switch. The fuel pump relay is controlled by the ECM. The relay is energized for 2 seconds with key on to provide fuel pressure for starting.

The oil pressure switch is provided as a backup. Normal operating engine oil pressure will close the normally open oil pressure switch contacts, providing a connection between circuit Nos. 239 and 120. If a relay fault occurs, the engine will continue to run as the oil pressure switch powers fuel pump.

The ECM monitors voltage on circuit No. 120 to detect fuel pump voltage faults. Code EO19 is set when fuel pump feedback circuit, ECM pin "D9", is at 11 volts or greater when the fuel pump feed voltage should be zero volts.

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

1. With key on/engine off, fuel pump should not be running and the fuel pump feedback (ECM parameter ED10) should be zero volts. The fuel pump is energized for 2 seconds with key on. After initial 2 second run, the fuel pump will not be powered until ECM sees distributor reference pulses from HEI.
2. This branch of diagnostic chart checks for shorted oil pressure switch contacts, powering fuel pump at all times.
3. Checks the ability of the fuel pump relay to provide power to fuel pump with a relay or relay drive circuit fault.
4. Checks for a short to the 12-volt power source in circuit No. 120.
5. Checks the ECM relay drive circuit for a fault that allows fuel pump relay coil to be energized continuously with key on.

Probe fuel pump test point with a voltmeter to ground. Turn key on and observe voltmeter. Voltmeter reading should be battery voltage for 2 seconds and then drop to zero. If voltmeter stays at battery voltage for longer than 2 seconds, check fuel pump relay contacts for sticking. Repeat this test several times.

Continue probing fuel pump test point to ground. Start engine and then turn it of. Voltage should drop immediately to zero. If not, check oil pressure switch for sticking contacts.

Review snapshot data parameters stored with this code to verify failure. If failure is verified, check and repair intermittent wiring connection or sensor.

Flow Chart, Code EO19, Shorted Fuel Pump Circuit. Scheme 218

Flow Chart, Code EO19, Shorted Fuel Pump Circuit. Scheme 219

ECM CODE EO20 - OPEN FUEL PUMP CIRCUIT (FUSE NOT BLOWN)

TEST CONDITIONS: Engine RPM greater than or equal to 24.

FAILURE CONDITIONS: Fuel pump feedback voltage less than or equal to 2 volts for 3 seconds or more.

ACTION: ECM stores code as current until engine is turned off. ECM turns on "ENGINE CONTROL SYSTEM" light. ECM commands BCM to display "SERVICE NOW" message on CCDIC panel.

The ECM monitors voltage on circuit No. 120 to detect fuel pump voltage faults. Code EO20 is set when ECM sees that fuel pump is not energized (zero volts on feedback circuit) with the engine cranking or running. Code is designed to detect a fuel pump relay fault (relay not powering fuel pump).

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

1. If engine starts with a current EO20 code, this indicates that engine started with fuel pump powered through the oil pressure switch. Fuel pump relay circuit may be at fault.
2. Zero volts with engine running indicates an open from fuel pump power circuit to ECM. Fuel pump relay is not at fault.
3. This step checks ECM's ability to energize relay coil.
4. This step checks for an open circuit from fuel pump 10-amp fuse to relay pin No. 1.
5. This step checks for an open circuit from relay pin No. 2 to ground.
6. If light turns on, then all circuitry is okay. Code may be caused by fuel pump relay.
7. Fault is most likely at ECM connector or ECM. See CHART C1 - ECM REPLACEMENT CHECK before replacing ECM.

If intermittent code EO20 is stored, unplug oil pressure switch. Start engine, allow it to idle, and manipulate affected wiring. Ensure that ECM connectors are properly latched and check relay for proper installation into relay center socket. If fault is induced, the engine will stall, and code EO20 will set. If code EO20 sets without an engine stall, cause is an intermittent open in circuit No. 120A between ECM pin "D9" and splice on circuit No. 120B.

Review snapshot data parameters stored with this code to verify failure. If failure is verified, check and repair intermittent wiring connection or sensor.

Flow Chart, Code EO20, Open Fuel Pump Circuit (1 Of 2). Scheme 220

Flow Chart, Code EO20, Open Fuel Pump Circuit (1 Of 2). Scheme 221

Flow Chart, Code EO20, Open Fuel Pump Circuit (2 Of 2). Scheme 222

ECM CODE EO20 - OPEN FUEL PUMP CIRCUIT (BLOWN FUSE)

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

1. With key on, light should be off, or light for 2 seconds as relay powers up fuel pump.
2. If a short circuit is present, it is in circuit No. 120, in fuel pump, or in ECM. Normal circuit resistance is 3-4 ohms.
3. Checks for ECM shorting circuit No. 120A to ground.
4. This step checks for short circuit in fuel tank.
5. This step checks fuel pump for short circuits, sending unit harness, and RFI suppression connector.
6. This step checks circuit No. 120 for a short to ground.
7. Check for a grounded fuel pump test point, connection at the relay center, and oil pressure switch. Also check harness for short to ground.
8. If light is on steadily, then the non-switched portion of the fuel pump circuit is shorted. Check circuit No. 239.

If fuel pump test point is grounded, the fuse will blow and code EO20 will set. If necessary, replace fuse. Start engine and allow it to idle. Manipulate affected wiring and connectors. If fault occurs, the fuse will blow and engine will stall.

Review snapshot data parameters stored with this code to verify failure. If failure is verified, check and repair intermittent wiring connection or sensor.

Flow Chart, Code EO20 (2 Of 2), Open Fuel Pump Circuit (Blown Fuse). Scheme 223

Flow Chart, Code EO20 (2 Of 2), Open Fuel Pump Circuit (Blown Fuse). Scheme 224

Test Conditions

Engine speed between 25-1000 RPM.

Failure Conditions

Throttle Position Sensor (TPS) value greater than or equal to 80 degrees for 3 seconds.

Action

ECM turns on "ENGINE CONTROL SYSTEM" light. ECM commands BCM to display "SERVICE SOON" message on CCDIC panel. ECM uses 12 degrees for TPS value when ISC throttle switch closes. ECM uses RPM for all ISC calculations (will not use TPS reading for coast down throttle control).

The TPS is a 3-wire sensor receiving a 5-volt reference input from ECM over circuit No. 474, and a reference ground from ECM over circuit No. 476. The TPS sends a sensor output signal over circuit No. 417 to the ECM.

The sensor output signal is a DC voltage that varies with throttle angle, the TPS signal voltage is low (about .5 volts at minimum air setting). At high throttle angles, the TPS signal voltage is high (about 4.5 volts at wide open throttle).

Code EO21 is set when the ECM sees a high throttle angle (high TPS voltage) at low engine RPM. Code is designed to detect a TPS signal, over circuit No. 417, shorted to voltage.

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

1. This step helps determine location of short to voltage. Short will be in TPS or circuit No. 417.
2. This step checks for an open ground in circuit No. 474. An open ground circuit will result in high TPS values whenever the TPS is plugged in.

If code EO21 is intermittent, manipulate related wiring and observe ECM parameter ED01. Check TPS connector for shorts to voltage.

Cycle TPS through its travel and tap on TPS with a pencil to test for intermittent TPS operation. If fault is induced, parameter will skip to high throttle angle. If wiring and connectors are okay, substitute a known good TPS sensor and retest.

Review snapshot data parameters stored with this code to verify failure. If failure is verified, check and repair intermittent wiring connection or sensor.

Flow Chart (2 of 2), Code EO21, Shorted TPS Circuit. Scheme 225

Note. If hard code EO21 is accompanied by hard code EO15, see DFI Chart A, "Multiple Codes Stored Hard".

Flow Chart Code EO21, Shorted TPS Circuit. Scheme 226

ECM CODE EO22 - OPEN TPS CIRCUIT

TEST CONDITIONS: Engine RPM is greater than or equal to 600.

FAILURE CONDITIONS: TPS value is less than -5 degrees (TPS parameter reads -10 to -6 degrees) for 1.5 seconds.

ACTION: ECM turns on "ENGINE CONTROL SYSTEM" light. ECM commands BCM to display "SERVICE SOON" message on CCDIC panel. ECM uses 12 degrees for TPS value with ISC throttle switch wide open, and 6 degrees for TPS value when ISC throttle switch closes. ECM stops using TPS to control ISC motor (it uses RPM for all ISC calculations).

The TPS is a 3-wire sensor receiving a 5-volt reference input from ECM over circuit No. 474, and a reference ground from ECM over circuit No. 476. The TPS sensor sends a sensor output signal over circuit No. 417 to the ECM.

The sensor output signal is a DC voltage that varies with throttle angle, the TPS signal voltage is low (about .5 volts at minimum air setting). At high throttle angles, the TPS signal voltage is high (about 4.5 volts at wide open throttle).

Code EO22 is set when the ECM sees a that throttle angle is out of limits (low TPS voltage) with engine running at idle or faster. Code is designed to detect a TPS signal, over circuit No. 417, open to ECM pin "D7".

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

1. Jumper 5 volts to TPS signal to see if ECM parameter will respond to high signal voltage on TPS inputs (circuit No. 417).
2. Checks for an open/shorted TPS reference circuit.
3. Checks for a grounded TPS signal (circuit No. 417).
4. Fault is most likely at ECM connector or ECM. See CHART C1 - ECM REPLACEMENT CHECK before replacing ECM.

If code EO22 is intermittent, manipulate related wiring while observing ECM parameter ED01. Cycle TPS through its travel and tap on TPS with a pencil to test for intermittent TPS operation. If fault is induced, parameter will skip to -6 degrees or less. If wiring and connectors are okay, substitute a known good TPS sensor and retest.

Review snapshot data parameters stored with this code to verify failure. If failure is verified, check and repair intermittent wiring connection or sensor.

Flow Chart, Code EO22, Open TPS Circuit. Scheme 227

Note. If a hard code EO22 is accompanied by hard code EO32, see DFI Chart A, "Multiple ECM Codes Stored Hard".

Code EO22, Open TPS Circuit. Scheme 228

Ignition on. Engine speed greater than or equal to 304 RPM.

EST pulses are seen by the ECM before by-pass circuit is turned on (5 volts) or EST signal remains grounded after the by-pass circuit is turned on (5 volts).

ECM turns on "ENGINE CONTROL SYSTEM" light. ECM commands BCM to display "SERVICE SOON" message on CCDIC. If ECM sees 5-volt EST pulses with by-pass voltage at zero, caused by EST circuit open or by-pass circuit shorted to voltage, the ECM will not enable spark timing. The engine will start and run on base timing. If EST circuit is shorted to ground, the vehicle will start and stall when engine reaches 300 RPM (as by-pass turns on). When restarted, the ECM will not try to turn by-pass on, code EO23 will set, and engine will start and run on base timing.

The EST distributor produces one 5-volt reference pulse each time that a cylinder reaches 10° BTDC (base timing). These reference pulses are sent from distributor to the ECM over circuit No. 430.

The ECM adds spark timing information to the reference pulses received from the HEI module and sends out a 5-volt electronic spark timing pulses over circuit No. 423.

The ECM can choose to control spark timing. The HEI by-pass circuit is turned on by the ECM when the ECM wishes to control timing. When timing control is desired, the HEI by-pass circuit is turned off and the HEI module ground circuit No, 423. The ECM always sends EST pulses to the HEI, the HEI module shorts EST pulses to ground when the by-pass signal from the ECM to module is low (less than .5 volts).

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

1. Four 12" jumper wires must be obtained for use in diagnostic procedure. Jumper wires MUST have male and female Weatherpack Connectors (12014836 and 12014837) on either end. With distributor connector unplugged, use jumper wires to reconnect terminals. Use instructions provided in chart.
2. With only distributor reference and distributor reference ground jumpered, engine will run on back-up spark control. This step checks for proper ground connection between ECM and engine, and between ECM and HEI.
3. This step ensures that ECM is providing an EST output signal over circuit No. 423.
4. This step checks the ability of the HEI module to ground EST signal with an open by-pass circuit.

Flow Chart, Code EO23, EST Circuit Problem (1 Of 2). Scheme 229

Flow Chart, Code EO23, EST Circuit Problem (1 Of 2). Scheme 230

Flow Chart, Code EO23, EST Circuit Problem (2 Of 2). Scheme 231

ECM CODE EO23 - EST CIRCUIT PROBLEM (2 OF 2)

The distributor reference ground (circuit No. 453) is a common ground between the ECM and HEI module. The ECM and HEI compare by-pass, EST, and reference voltages to ground voltage on circuit No. 453. An open circuit No 453 to the HEI or ECM can cause a failure of the ECM to recognize a reference pulse or the HEI module to recognize an EST pulse.

The ECM compares status of EST circuit to status of by-pass circuit in order to detect a fault and set code EO23. If ECM has by-pass at 5 volts, the module should accept EST information, and EST voltage should be high (.5-2.8 volts). If by-pass is at zero volts, module should ground EST circuit and the EST voltage should be low (less than .5 volts). Possible causes of code EO23 are

1. Circuit No. 423 (EST) open or grounded.
2. Circuit No. 424 (by-pass) open or grounded.
3. Circuit No. 453 (reference ground) open to ground at HEI module or ECM.
4. ECM has poor connection to engine through circuit No. 450 (ground).
5. ECM or HEI module faulty. NOTE: Test numbers refer to test numbers on diagnostic chart.

1. 5) This step checks HEI module's ability to recognize a voltage on by-pass circuit and to top grounding EST (ECM controlled timing).
2. 6) This step checks for by-pass signal to module. If by-pass signal is being sent by ECM to HEI, and if module is interpreting by-pass voltage correctly, then module will switch off ground to EST.
3. 7) If chart leads to "EST CIRCUIT IS OK", then a fault may exist in the 4-way connector. Check connector and terminals for damage. If connector is okay, plug in connector and retest for code EO23.

Flow Chart, Code EO23, EST Circuit Problem (2 Of 2). Scheme 232

Flow Chart, Code EO23, EST Circuit (1 Of 2). Scheme 233

Flow Chart, Code EO23, EST Circuit (2 Of 2). Scheme 234

ECM CODE EO24 - SPEED SENSOR CIRCUIT PROBLEM

TEST CONDITIONS: Codes EO26, EO27, EO28, EO31, EO32, and EO34 clear. Transmission in reverse or drive, and brake switch closed (not braking). ISC throttle switch open. MAP less than or equal to 85 kPa (Kilopascals). Transmission in 4th gear (4th gear switch open). Engine speed greater than or equal to 1400 RPM.

FAILURE CONDITIONS: Vehicle speed equals zero MPH for 3 seconds.

ACTION: ECM turns on "ENGINE CONTROL SYSTEM" light. ECM commands BCM to display "SERVICE SOON" on CCDIC panel. Viscous Converter Clutch (VCC) and cruise control disabled. Use vehicle speed information coming from BCM serial data.

The Vehicle Speed Sensor (VSS) is a permanent magnet pulse generator that is geared to transmission output to create 4000 voltage pulses per mile. The BCM receives speed sensor signal from VSS, changes signal to 2000 pulses per mile, then sends the 2000 pulse signal to the ECM over circuit No. 437.

The ECM uses VSS input for VCC apply and release determinations, to select between RPM and throttle angle control of ISC, and as a test condition for many codes.

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

1. Checks for proper voltage from BCM at ECM connector.
2. This step checks for voltage sent from BCM.
3. Before replacing ECM or BCM, unplug and plug in connectors to ensure that they are latched properly.

Backprobe ECM pin "C8" with a voltmeter to ground. Lift both drive wheels off ground, start engine and allow it to idle in drive. Manipulated affected wiring and watch for sudden loss of voltage on ECM pin "C8".

Review snapshot data parameters stored with this code to verify failure. If failure is verified, check and repair intermittent wiring connection or sensor.

Schematic, Code EO24, Speed Sensor Circuit Problem. Scheme 235

Flow Chart, Code EO24, Speed Sensor Circuit Problem. Scheme 236

Flow Chart, Code EO24, Speed Sensor Circuit Problem. Scheme 237

ECM CODE EO26 - SHORTED THROTTLE SWITCH CIRCUIT

TEST CONDITIONS: Code EO21 and EO22 clear. TPS position greater than 14 degrees. TPS voltage less than 4.5 volts (about 80 degrees).

FAILURE CONDITIONS: Throttle switch input to ECM grounded (throttle switch closed).

ACTION: ECM turns on "ENGINE CONTROL SYSTEM" light. ECM commands BCM to display "SERVICE SOON" message on CCDIC panel. ECM assumes closed throttle if brakes are applied or TPS position is less than or equal to 12 degrees. ECM assumes open throttle when brakes are off or TPS position is more than 12 degrees.

The throttle switch is part of ISC motor assembly. Pin "B" of ISC motor 4-pin connector is the throttle switch input to the ECM. The ECM provides a 4.5-6.0 voltage signal to pin "B" of ISC. When throttle lever contacts ISC plunger, throttle switch closes, shorting voltage signal at pin "B" to pin "A" which is a ground (closed throttle equals throttle switch input voltage low).

Code EO26 is designed to detect a throttle switch input that is always grounded and/or throttle switch never opens.

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

1. Code EO26 is set due to throttle switch input shorted to ground or ISC throttle switch inoperative. This should result in ECM input EI72 not cycling. ECM input EI72 code will be low at all times.
2. This step checks for TPS reading too high. TPS fault or misadjustment that results in a reading above 14 degrees at closed throttle, which will cause a false code EO26.
3. Checks for TPS too high due to TPS or TPS circuit.
4. If TPS and circuit are both okay, ECM should be checked. See CHART C1 - ECM REPLACEMENT CHECK.

Select ECM input code EI72. Manipulate affected wiring and connectors and observe for throttle switch status to change. Check for intermittent ground on circuit No. 427.

Select ECM data code ED01. Manipulate affected wiring and connectors. Watch for TPS value to go above 14 degrees at closed throttle. Tap lightly on TPS with pencil to check for intermittent TPS operation. Check for binding TPS lever, intermittent open on circuit No. 476, or intermittent short to 5 volts on circuit No. 417 at TPS.

Flow Chart, Code EO26, Shorted Throttle Switch Control. Scheme 238

Flow Chart, Code EO26, Shorted Throttle Switch Control. Scheme 239

ECM CODE EO27 - OPEN THROTTLE SWITCH CIRCUIT

TEST CONDITIONS: Always tested.

FAILURE CONDITIONS: Throttle switch was never closed during last key cycle. Throttle switch has not closed in current key cycle.

ACTION: ECM turns on "ENGINE CONTROL SYSTEM" light. ECM commands BCM to display "SERVICE SOON" message on CCDIC panel. ECM assumes throttle switch is closed if TPS position is less than or equal to 12 degrees, and brake switch is open (braking).

The throttle switch is part of ISC motor assembly. Pin "B" of ISC motor 4-pin connector is the throttle switch input to the ECM. The ECM provides a 4.5-6.0 voltage signal to pin "B" of ISC. When throttle lever contacts ISC plunger, throttle switch closes, shorting voltage signal at pin "B" to pin "A", which is a ground (closed throttle equals throttle switch input voltage low). Code EO27 is designed to detect a throttle switch that is always open.

Note. Test number refers to test number on diagnostic chart.

1. Code EO27 is due to throttle switch input open, ISC throttle switch inoperative, and should result in ECM input code EI72 not cycling. ECM input code EI72 will be high at all times.

Check for binding throttle shaft and throttle blades, weak or distorted throttle spring, cruise control or throttle valve cable binding, or properly installed TPS. Intermittent code EO27 can be induced by resting foot on accelerator with key on/key off for 10 seconds, during key on cycle.

Schematic, Code EO27, Open Throttle Switch Circuit. Scheme 240

Flow Chart, Code EO27, Open Throttle Switch Circuit. Scheme 241

Flow Chart, Code EO27, Open Throttle Switch Circuit. Scheme 242

Code EO24 clear. Transmission in park or neutral. Vehicle speed less than or equal to 4 MPH.

Third gear input to ECM not grounded. Fourth gear input to ECM not grounded.

ECM turns on "ENGINE CONTROL SYSTEM" light. ECM commands BCM to display "SERVICE SOON" message on CCDIC panel.

The 3rd and 4th gear switches, in transmission, are normally closed switches that are opened by transmission oil pressure. The ECM sends a 12-volt signal to each switch. When not in 3rd or 4th gear, 3rd and 4th gear inputs are grounded by normally closed switches.

When 3rd gear is achieved, 3rd gear switch is opened by 3rd gear oil pressure, and 3rd gear input changes from zero volts to 12 volts. When 4th gear is achieved, 4th gear switch is opened by 4th gear oil pressure, and 4th gear input changes from zero volts to 12 volts. Code EO28 is designed to detect a false 3rd or 4th gear indication to ECM.

With key on, engine off, and transmission in "PARK" position, manipulate affected wiring and connectors while observing 3rd/4th gear status light. If 3rd or 4th gear status indicator comes on, repair intermittent open in circuit No. 438 (3rd gear) or circuit No. 446 (4th gear).

Review snapshot data parameters stored with this code to verify failure. If failure is verified, check and repair intermittent wiring connection or sensor.

Flow Chart (1 of 2), Code EO28, Open 3rd Or 4th Gear Circuit. Scheme 243

Flow Chart, Code EO28, Open 3rd Or 4th Gear Circuit (1 Of 2). Scheme 244

Flow Chart, Code EO28, Open 3rd Or 4th Gear Circuit (2 Of 2). Scheme 245

Flow Chart, Code EO28, Open 3rd Or 4th Gear Circuit (2 Of 2). Scheme 246

Codes EO21, EO22, EO24, EO26 and EO27 clear. Vehicle speed equals zero. Throttle switch closed. Battery voltage greater than or equal to 11 volts. Engine speed is greater than 152 RPM, which is different than desired. Not a cold start.

ISC plunger extending with TPS position less than or equal to 9 degrees or ISC retracting with TPS position greater than or equal to 2.5 degrees for 15 seconds.

ECM turns on "ENGINE CONTROL SYSTEM" light. ECM commands BCM to display "SERVICE SOON" message on CCDIC panel.

The ECM controls engine idle by increasing or decreasing throttle opening using the Idle Speed Control (ISC) motor. The ISC will be active in controlling idle speed any time throttle switch is closed.

At vehicle speeds less than 6 MPH, the ECM controls idle speed based on engine RPM. When vehicle speed is greater than 6 MPH, the ECM controls idle speed based primarily on throttle opening (TPS) with adjustments to maintain a minimum engine RPM. Code EO30 is designed to detect engine RPM out of limits high or low.

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

1. This step checks for TPS misadjusted.
2. This step checks for proper throttle switch, power steering switch, and park/neutral switch operation. The ECM must receive accurate switch status information in order to control idle.
3. This step checks for proper ISC motor operation.
4. Many engine fuel and emissions system faults may cause unstable idle. If base engine idle is not steady, ISC may not be able to control idle to within 150 RPM of desired idle.
5. Minimum air rate, ISC, TPS, or ISC motor out of adjustment. Minimum air rate or TPS can cause ISC not to control idle, or code EO30 to set falsely.
6. Checks ISC motor circuits for proper operation. Throttle switch input to ECM must be jumpered in order to allow ISC to cycle.

Display ECM parameter ED01, manipulate TPS wiring and connectors, and see if TPS valve jumps or skips. Enter ECM input EI72, observe throttle switch status light, and check for binding throttle linkage or weak throttle return spring.

Verify that minimum air rate RPM, ISC and TPS are set to specifications. A code EO30 may be stored along with a code EO19, SHORTED FUEL PUMP CIRCUIT. If code EO30 no longer appears after code EO19 has been corrected, do not investigate any further. The voltage on fuel pump feedback circuit made ECM improperly test code EO30.

Review snapshot data parameters stored with this code to verify failure. If failure is verified, check and repair intermittent wiring connection or sensor.

Flow Chart, Code EO30, Idle Speed Control Circuit Problem. Scheme 247

Flow Chart, Code EO30, Idle Speed Control Circuit Problem (1 Of 2). Scheme 248

Flow Chart, Code EO30, Idle Speed Control Circuit Problem (2 Of 2). Scheme 249

Always tested.

MAP value greater than 105 kPa (106-109 Kilopascals = kPa) for at least .2 seconds.

ECM turns on "ENGINE CONTROL SYSTEM" light. ECM commands BCM to display "SERVICE NOW" message on CCDIC panel. ECM turns off AIR management solenoids. ECM uses a substitute MAP sensor value from MAP versus RPM table when throttle switch is closed. ECM uses a substitute MAP sensor value of 81.8 kPa with open throttle switch. ECM assumes that barometric pressure value is 92.2 kPa.

The MAP sensor output signal voltage is a DC voltage that varies with manifold absolute pressure. As MAP decreases, voltage decreases (low engine load, high vacuum). As MAP increases, voltage increases (high engine load, low vacuum).

The ECM uses MAP sensor values as an indicator of engine load. A high MAP reading indicates heavy load, and low MAP reading indicates low load. Code EO31 is designed to set when ECM detects a MAP sensor signal out of high limits, MAP signal at 4.85 volts or more, and having a value greater than 105 kPa.

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

1. If ECM parameter ED02 goes to 14-16 kPa with sensor unplugged, fault is at MAP sensor or sensor connector.
2. This step checks for an open circuit from pin "A" of sensor connector to ECM pin "D12" (ground). If ground is open, sensor cannot divide reference voltage to make signal voltage vary. The signal voltage is always high.

Manipulate affected wiring and connectors while observing ECM parameter ED02. Apply and release vacuum to MAP sensor vacuum port using a vacuum source. If ECM parameter code ED02 displays greater than 105 kPa, condition has been induced and cause of intermittent should be repaired. If wiring and connectors are okay, substitute a known good sensor and retest.

Review snapshot data parameters stored with this code to verify failure. If failure is verified, check and repair intermittent wiring connection or sensor.

Flow Chart, Code EO31, Shorted MAP Sensor Circuit. Scheme 250

Note. If a hard code EO31 is accompanied by a hoard code EO38, See DFI Chart A, "Multiple ECM Codes Stored Hard".

Flow Chart, Code EO31, Shorted MAP Sensor Circuit. Scheme 251

With ISC throttle switch closed, engine speed at less than or equal to 700 RPM, TPS position should be less than or equal to 12 degrees. With ISC throttle switch open, TPS position should be greater than or equal to 9.6 degrees.

MAP value less than 16 kPa (Kilopascals).

The ECM turns on "ENGINE CONTROL SYSTEM" light. ECM commands BCM to display the "SERVICE NOW" message on CCDIC panel. ECM turns off both AIR management solenoids. ECM uses a substitute MAP sensor value of 81.8 kPa with open throttle switch. ECM uses a substitute MAP value from a MAP versus RPM table if throttle switch is closed. ECM uses a substitute barometric pressure value of 92.2 kPa.

The MAP sensor output voltage is a DC voltage that varies with MAP. As MAP decreases, voltage on circuit No. 432 decreases (low engine load, high engine vacuum). As MAP increases, voltage on circuit No. 432 increases (high engine load, low engine vacuum). Code EO32 is designed to set when ECM detects a MAP sensor signal out of low limits (MAP signal at 16 kPa or less and MAP voltage at .08 volts or less).

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

1. This step checks ECM's ability to respond to a 5-volt signal on MAP input. A reading of 106-109 kPa means wiring and ECM are okay.
2. This step checks for 5-volt reference signal present at sensor connector.
3. This step checks circuit No. 432 for short to ground.
4. This step checks ECM's ability to respond to a 5-volt signal voltage on MAP input.
5. Fault is most likely at ECM connector or ECM. See CHART C1 - ECM REPLACEMENT CHECK, before ECM is replaced.

NOTES ON INTERMITTENT

Code EO32 can be set by an open 5-volt reference signal between ECM and sensor, an open MAP signal between sensor and ECM, or a defective MAP sensor.

Manipulate affected wiring and connectors while observing ECM parameter ED02. Apply and release vacuum to MAP sensor vacuum port using a vacuum source. If ECM parameter ED02 displays less than 17 kPa, condition has been induced and cause of intermittent can be repaired. If wiring and connectors are okay, substitute a known good sensor and retest.

Review snapshot data parameters stored with this code to verify failure. If failure is verified, check and repair intermittent wiring connection or sensor.

Flow Chart, Code EO32, Open MAP Sensor Circuit. Scheme 252

Note. If a hard code EO32 is accompanied by a hard code EO22, see DFI Chart A, "Multiple ECM Codes Stored Hard".

Flow Chart, Code EO32, Open MAP Sensor Circuit. Scheme 253

Codes EO21, EO22, EO26, EO27, EO31 and EO32 clear. Key is on. Engine speed greater than or equal to 400 RPM. Throttle switch closed. TPS position less than or equal to 12 degrees. Barometric (BARO) pressure greater than or equal to 75 kPa (Kiloapascals).

MAP value within 6 kPa of barometric value for 2.1 seconds.

EMC turns on "ENGINE CONTROL SYSTEM" light. ECM commands BCM to display "SERVICE NOW" message on CCDIC panel. ECM turns off both AIR management solenoids. ECM uses a substitute MAP sensor value of 81.8 kPa with throttle switch open. ECM looks up a substitute MAP sensor value from a MAP versus RPM table, when throttle switch is closed.

The MAP sensor output voltage is a DC voltage that varies with MAP. As MAP decreases, voltage on circuit No. 432 decreases (low engine load and high engine vacuum). As MAP increases, voltage on circuit No. 432 increases (high engine load and low engine vacuum).

The ECM uses MAP sensor reading as an indicator of engine load. Low MAP readings mean low engine load, and high MAP readings mean high engine load. Code EO34 is designed to set when ECM detects a MAP sensor signal that is much too high for closed throttle test conditions. Code EO34 usually indicates that there is fault in vacuum supply to MAP sensor.

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

1. MAP at idle should be 30-60 kPa, depending on engine load. BARO pressure should be 85-105 kPa depending upon altitude.
2. Check for vacuum at MAP sensor hose with vacuum gauge. At idle, typical vacuum readings are 15-20 in. Hg, depending on engine load.
3. Checks for faulty MAP sensor vacuum supply or MAP sensor circuitry.
4. Checks for sensor ground open from sensor to ECM.
5. Checks for a short to the voltage on sensor signal circuit No. 432.
6. Fault is at ECM connector or ECM. See CHART C1 - ECM REPLACEMENT CHECK, before ECM is replaced.

NOTES ON INTERMETTENTS

Code EO34 is usually set by a vacuum supply problem to MAP sensor. Check for proper vacuum routing for MAP hose connected to proper throttle body port, or MAP hose chafed, pinched or cut. Apply vacuum to MAP hose at throttle body, and look for vacuum leaks in MAP hose or MAP sensor.

Manipulate affected wiring and connections while observing ECM parameter ED02. If ECM parameter jumps or skips high with vacuum applied, the condition has been induced and cause of intermittent can be repaired. If wiring and connectors are okay, substitute a known good sensor and retest.

Review snapshot data parameters stored with this code to verify failure. If failure is verified, check and repair intermittent wiring connections or sensor.

Flow Chart, Code EO34, MAP Signal Too High. Scheme 254

Flow Chart, Code EO34, MAP Signal Too High. Scheme 255

Codes EO14 and EO15 are clear. Coolant sensor less than or equal to 105°C.

MAT sensor value is greater than or equal to 142°C

ECM turns on "ENGINE CONTROL SYSTEM" light. ECM commands BCM to display "SERVICE SOON" message on CCDIC panel. ECM turns off both AIR management solenoids. ECM substitutes 40°C for MAT when coolant is greater than or equal to 40°C. ECM uses coolant temperature for MAT when coolant temp is less than or equal to 40°C.

The MAT sensor is a variable thermistor that varies its resistance with temperature. The MAP sensor is a 2-wire sensor with a reference or signal voltage coming from the ECM to sensor pin "B" over circuit No. 472, and a sensor reference ground on pin "A" over circuit No. 476.

As temperature of sensor increases, sensor resistance is lower. The signal voltage from ECM to pin "B" decreases as sensor temperature increases, current flows from pin "B" through sensor element to pin "A", sensor ground.

High temperature means low signal voltage on circuit No. 472, and low temperature means high signal voltage on circuit No. 472. Code EO37, shorted MAT sensor, sets because ECM assumes that MAT can not be 142°C or greater with a coolant temperature of less than 105°C.

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

1. With a shorted sensor, ECM parameter Code ED05 should read 142°C or greater. If not, sensor is not shorted. See NOTES ON INTERMITTENTS.
2. Check for sensor short or circuit No. 472 shorted. If ECM parameter EDO5 stays at 142-151°C with sensor unplugged, short is in circuit No. 472.
3. Fault is most likely at ECM connector or ECM. See CHART C1 - ECM REPLACEMENT CHECK, before ECM is replaced.
4. MAT sensors can be damaged by a backfire in the intake. If vehicle has had more than one MAT sensor replaced, check for signs of backfire or high intake manifold temperatures due to improper valve train operation.

Manipulate circuit No. 472 wiring, MAT sensor and ECM connector, while observing ECM parameter ED05. If failure is induced, manifold air temperature will jump from its normal value to shorted reading of 142-151°C. If wiring and connectors are okay, substitute a known good sensor and retest.

Review snapshot data parameters stored with this code to verify failure. If failure is verified, check and repair intermittent wiring connections or sensor.

Flow Chart, Code EO27, Shorted MAT Sensor Circuit. Scheme 256

Flow Chart, Code EO27, Shorted MAT Sensor Circuit. Scheme 257

Codes EO14 and EO15 are clear. Coolant temperature sensor greater than or equal to -5°C.

MAT sensor value less than -35°C.

ECM turns on "ENGINE CONTROL SYSTEM" light. ECM commands BCM to display "SERVICE SOON" message on CCDIC panel. ECM turns off both AIR management solenoids. ECM uses 40°C for a MAT value when coolant temperature is greater than 40°C. ECM substitutes coolant temperature for MAT when coolant temperature is less than 40°C.

The MAT sensor is a variable thermistor that varies its resistance with temperature. The MAT sensor is a 2-wire sensor with a reference or signal voltage coming from ECM to sensor pin "B" over circuit No. 472, and a sensor reference ground on pin "A" over circuit No. 476. As temperature of sensor decreases, sensor resistance increases.

The signal voltage from ECM to pin "B" increases as sensor temperature decreases, as less current flows from sensor pin "B" through sensor element to ground. Less of signal voltage is dropped across sensor element. Low temperature means high signal voltage on circuit No. 472, and high temperature means low signal voltage on circuit No. 472.

Code EO38, open MAT sensor, sets because the ECM assumes that MAT can't be -35°C to -40°C with coolant temperature of -5°C or more.

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

1. If sensor is open, ECM parameter ED05 should read -35°C or less. If not, sensor signal is not open at this time. See NOTES ON INTERMITTENTS.
2. Check ECM and sensor circuitry from ECM to sensor connector. If ECM parameter ED05 reads 142-151°C with connector pin "A" shorted to pin "B", sensor circuits and ECM are okay.
3. This steps checks for open sensor ground.
4. This steps checks for ECM's ability to recognize short to ground on MAT input.
5. Fault is most likely at ECM connector or ECM. See CHART C1 - ECM REPLACEMENT CHECK, before ECM is replaced.
6. MAT sensor can be damaged by backfire in intake, or by excessive intake heat due to valve train faults. If vehicle has had multiple MAT sensor replacements, check for signs of backfire or high intake manifold air temperature due to improper valve train operation.

Manipulate circuits No. 472 and 476 wiring, MAT connector, and ECM connector while observing ECM parameter ED05. If failure is induced, MAT will jump from its normal value to open signal circuit reading of -35°C to -40°C. If wiring and connectors are okay, substitute a known good sensor and retest.

Review snapshot data parameters stored with this code to verify failure. If failure is verified, check and repair intermittent wiring connections or sensor.

Flow Chart, Code EO38, Open MAT Sensor Circuit. Scheme 258

Flow Chart, Code EO38, Open MAT Sensor Circuit. Scheme 259

Code EO28 is clear. Transmission is in 4th gear. Throttle switch open and engine in closed loop. Not accelerating or decelerating. Transmission not in park or neutral. Not braking or VCC engaged.

Engine RPM too high for vehicle speed. ECM has a 9 place table of speed compared to RPM. If RPM exceeds RPM for speed listed in table for 8 seconds, code EO39 will set. At 40 MPH, RPM should be 1650. AT 50 MPH, RPM should be less than or equal to 1790. At 60 MPH, RPM should be less than or equal to 1994 RPM.

ECM turns on "ENGINE CONTROL SYSTEM" light. ECM commands BCM to display "SERVICE SOON" message on CCDIC panel.

The Viscous Converter Clutch (VCC) solenoid is turned on when ECM applies ground to circuit No. 422. The power for VCC solenoid comes from 15 amp "IGN-1" fuse in fuse block. Power flows through VCC brake switch to pin "A" of 5-pin connector on transmission. At pin "A", current flows into transmission to VCC solenoid, and then to transmission over-temperature switch.

The transmission over-temperature switch is normally closed and opens when transmission sump temperature is 157°C or greater. This disables VCC and allows transmission to cool. From over-temperature switch, current returns to ground through the ECM.

Code EO39 is set when engine RPM exceeds normal value from a given speed with VCC applied. With VCC applied, the engine is coupled directly to transmission through the VCC. Almost no slippage should occur, so the RPM/speed ratio is nearly constant. If RPM is too high at a given speed, the ECM senses that VCC is slipping or not applied, and code EO39 is set.

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

1. Check for continuity from fuse through solenoid to circuit No. 422.
2. This steps checks for ECM's ability to ground solenoid.
3. Circuit is okay. Check for transmission hydraulic system faults.

The vehicle must be driven for 30 seconds in test conditions for code EO39 to occur. This may necessitate an extended test drive of at least 15 minutes of operation at above 45 MPH.

If customer complaint indicates that code occurs after an extended drive, check for signs of transmission overheating. Transmission sump oil temperatures in excess of 157°C will cause transmission over-temperature switch to open the VCC solenoid circuit and disable VCC. If no trouble can be found, check transmission for internal problems.

Flow Chart, Code EO39, VCC Engagement Problem. Scheme 260

Note. This procedure must not be followed if a code EO16, EO24 or EO59 is current.

Flow Chart, Code EO39, VCC Engagement Problem. Scheme 261

Vehicle speed greater than or equal to 40 MPH.

Power steering switch opens (ECM sees zero volts on pin "D8", steering input, for 10 seconds).

ECM turns on "ENGINE CONTROL SYSTEM" light. ECMcommands BCM to display "SERVICE SOON" message on CCDIC panel.

The power steering pressure switch is normally closed and opens with power steering pressure. The power steering pressure switch receives 12 volts from 10-amp solenoid fuse on circuit No. 639E, and sends 12-volt signal to ECM on circuit No. 495.

When high power steering pressures occur, switch contacts are opened by power steering oil pressure and circuit No. 495 voltage is read by ECM as zero volts.

ECM uses power steering switch input to extend ISC, when high power steering loads occur to help maintain a stable idle speed.

Test drive car above 45 MPH while observing ECM input E178. Input E178 should be high at all times. If E178 reads low at any time, without turning the steering wheel to full lock, check for intermittent open in circuit No. 639.

Also check for intermittent open in circuit No. 495 to the ECM. Manipulate power steering pressure switch connector in circuit No. 495 wiring and ECM connector while observing test light. If light goes out, repair intermittent open or short to ground.

Review snapshot data parameters stored with this code to verify failure. If failure is verified, check and repair intermittent wiring connections or sensor.

Flow Chart, Code EO40, Open Power Steering Pressure Switch Circuit. Scheme 262

Flow Chart, Code EO40, Open Power Steering Pressure Switch Circuit. Scheme 263

Codes EO14, EO15, EO16, EO21, EO22, EO26, EO27, EO31, EO32, and EO34 clear. Throttle switch open. TPS between 6 and 29 degrees. Coolant sensor greater than or equal to 80°C. Oxygen sensor ready (closed loop). Not accelerating or decelerating. RPM greater than or equal to 800.

Oxygen sensor status stays lean for more than 45 seconds.

ECM turns on "ENGINE CONTROL SYSTEM" light. ECM commands BCM to display "SERVICE NOW" message on CCDIC panel. ECM turns on canister purge solenoid and turns off AIR management solenoids. ECM switches to open loop operation.

The ECM provides a .45-volt reference signal to oxygen sensor on circuit No. 412. When oxygen sensor is cold, less than 200°C, oxygen sensor signal voltage will be about .45 volt. The ECM will keep system in open loop operation. When oxygen sensor is warm, greater than 200°C, oxygen sensor signal voltage will change from rich to lean rapidly. At least one change every 2 seconds, if ECM is in good control of air/fuel mixture.

When ECM sees that oxygen is varying from cold voltage of .45-volt, it will send system into closed loop operation. In closed loop operation, ECM will adjust fuel delivery rate to engine based on oxygen sensor readings.

Code EO44 is designed so that if oxygen sensor stays at lean voltage for more than 45 seconds during test conditions, code EO44 will set. Code EO44 will set when there is an oxygen sensor circuit fault giving a false lean indication, or when air/fuel ratio is actually lean due to a vacuum leak or fuel control system fault.

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

1. With oxygen sensor disconnected, parameter ED07 should remain at reference voltage (.38-.63 volts).
2. Check for sensor circuitry ability to record rich readings. The DVOM set on volts will provide a few billionths of an amp to drive circuit No. 412 to above .64 volts (rich). Similar results may be obtained by placing a finger on battery positive terminal and another finger oxygen sensor circuit No. 412 harness terminal.
3. The ECM compares oxygen sensor signal voltage received on circuit No. 412 to ground voltage on circuit No. 413. If ECM does not have a good ground to engine on circuit No. 413, oxygen sensor can appear falsely high or low. With engine running, use a voltmeter to measure voltage from oxygen sensor at exhaust manifold to ECM terminal "A1". If the voltage is -.05 to +.05 volts, the ground is okay. If voltage is less than -.05 volts or greater than +.05 volts, repair poor ground on circuit No. 413 between ECM terminal "A1" and ground at front of engine (right rearmost cylinder head).

With engine running, manipulate oxygen sensor, ECM wiring and connectors while observing ECM parameter ED07. If fault is induced, ED07 will jump below .37 volts, and "ECON" status light will go off. Manipulate circuit No. 413 ground to engine, and look for a loose ground eyelet or ground eyelet installed at wrong location. If lean engine operation is suspected, perform DFI SYSTEM CHECK. If oxygen sensor circuit seems to be okay, go to CHART A9 - OXYGEN SENSOR DIAGNOSIS.

Review snapshot data parameters stored with this code to verify failure. If failure is verified, check and repair intermittent wiring connections or sensor.

Flow Chart, Code EO44, Lean Exhaust Signal. Scheme 264

Flow Chart, Code EO44, Lean Exhaust Signal. Scheme 265

Codes EO14, EO15, EO16, EO21, EO22, EO26, EO27, EO31, EO32, and EO34 clear. Throttle switch open. TPS between 6 and 29 degrees. Coolant sensor greater than or equal to 80°C. Oxygen sensor ready (closed loop). Not accelerating or decelerating. RPM greater than or equal to 800.

Oxygen sensor stays rich for more than 45 seconds.

ECM turns on "ENGINE CONTROL SYSTEM" light. ECM commands BCM to display "SERVICE NOW" message on CCDIC panel. ECM turns on canister purge solenoid and turns off AIR management solenoids. ECM switches to open loop operation.

The ECM provides a .45-volt reference signal to oxygen sensor on circuit No. 412. When oxygen sensor is cold (below 200°C), output voltage will be about .45 volts. The ECM will keep system in open loop operation. When warm, a properly operating oxygen sensor will drive the .45-volt reference lower (below .45 volts) to indicate a rich mixture. Oxygen sensor signal voltage will swing from rich to lean rapidly. This will happen at least one swing every 2 seconds, if ECM is in good control of air/fuel mixture.

When ECM sees that oxygen is not at cold voltage of .45 volts, it will send system into closed loop operation. In closed loop operation, ECM will meter fuel into engine based on oxygen sensor readings.

Code EO45 is designed so that if oxygen sensor stays at rich voltage for more than 45 seconds during test conditions, code EO45 will set. Code EO45 will set when oxygen sensor circuit fails or when air/fuel ratio is actually rich due to fuel control or emissions system fault.

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

1. With oxygen sensor disconnected, parameter ED07 should remain at reference voltage (.38-.63 volts).
2. This steps checks for ECM's ability to recognize lean input on oxygen sensor signal circuit No. 412.
3. The ECM compares oxygen sensor signal voltage received on circuit No. 412 to ground voltage on circuit No. 413. If ECM does not have a good ground to engine on circuit No. 413, oxygen sensor can appear falsely high or low. With engine running, use a voltmeter to measure voltage from oxygen sensor at exhaust manifold to ECM terminal A1. If voltage is -.05 to +.05 volts, the ground is okay. If voltage is less than -.05 volts or greater than +.05 volts, repair poor ground on circuit No. 413 between ECM terminal "A1" and ground at front of engine or right rear cylinder head.

With engine running, manipulate oxygen sensor, ECM wiring and connectors while observing ECM parameter ED07. If fault is induced, ED07 will jump above .63 volts, and "ECON" status light will go on. Manipulate circuit No. 413 ground to engine, and look for a loose ground eyelet or ground eyelet installed at wrong location. If oxygen sensor circuit is okay or lean engine operation is suspected, perform DFI SYSTEM CHECK.

Review snapshot data parameters stored with this code to verify failure. If failure is verified, check and repair intermittent wiring connections or sensor.

Flow Chart, Code E045, Rich Exhaust Signal. Scheme 266

Flow Chart, Code E045, Rich Exhaust Signal. Scheme 267

Code EO18 is clear and engine not cranking.

ECM receives bad data or no data from BCM for 2.1 seconds.

ECM clears all BCM data from ECM memory. ECM assumes that A/C clutch is on at all times and controls ISC motor operation accordingly. ECM turns on "ENGINE CONTROL SYSTEM" light. ECM tries to send "SERVICE SOON" message to BCM over data link.

The ECM and BCM share information through data link. The BCM is in control of data link and data is only transmitted at the BCM's request. Data is sent in eight character words at a rate of 8192 characters per second. The data from the ECM to the BCM contains power steering pressure switch, park/neutral switch, 4th gear switch, engine running, and coolant temperature sensor information. The ECM/BCM data also includes coolant temperature sensor, RPM and injector pulse width information to control the cooling fans, display RPM and calculate MPG for display. The BCM sends the ECM air conditioning status to be used for idle speed control and ambient temperature for use in VCC application and release.

Code EO47 is set in the ECM in the event of a data link failure. If it's a hard failure, the ECM will not be able to communicate with the BCM and Code B334 will be current. Code EO47 is current in the ECM but cannot be sent (displayed) to BCM because of data link fault. If data link fault is corrected, both code E047 and B334 will be displayed as history codes. Code E047 can only be displayed as an intermittent. If fault is present, code B334 will be current. Diagnose problem using BCM CODE B334, LOSS OF ECM DATA chart. Three failures can result in a code E047

1. Open in circuit No. 800/800H between ECM pin "C9" and data link. The symptoms will be: A "SYSTEM PROBLEM" message on CCDIC panel. B "ENGINE CONTROL SYSTEM" and "CHECK INFO CENTER" lights on. C Diagnostics entered and "NO ECM DATA" is displayed on CCDIC panel. D When repaired, diagnostics will show code EO47 as history and code B334 as current codes until key is cycled to off.
2. Grounded circuit No. 800/800H from ECM pin "C9" to data link. Symptoms will be: A "SYSTEM PROBLEM" message on CCDIC panel. B "ENGINE CONTROL SYSTEM" light on. C Speedometer is blank at instrument cluster. D A/Cheater system goes to 75°F and defrost, cooling fan goes to high. E Diagnostics disabled, "SYSTEM PROBLEM" message stays on CCDIC panel. F When repaired, diagnostics will show codes E047, B334, B335, B336 and B337 as history codes.
3. Open ECM Memory-Calibration Unit (MEM-CAL unit contains communications instructions for the ECM). Symptoms will be the same as grounded circuit No. 800/800H.

Schematic, Code EO47, BCM-To-ECM Data Problem. Scheme 268

Codes EO13, EO14, EO15, EO21, EO22, EO31, EO32, EO34, EO44, and EO45 clear. Coolant temperature is between 85-110°C. TPS between 8-15 degrees. RPM between 1450-1650. Oxygen sensor in closed loop operation.

If oxygen sensor fails to indicate a leaner mixture in at least 3 of 5 tests, code EO48 is set.

ECM turns on "ENGINE CONTROL SYSTEM" light. ECM commands BCM to display "SERVICE SOON" message on CCDIC panel. EGR is disabled for the entire key cycle.

To perform test, the ECM turns off EGR flow to engine and monitors oxygen sensor (closed loop) integrator. With EGR turned off, the integrator should swing to a higher value reflecting leaner air/fuel mixtures. If not, the ECM assumes that either EGR was turned off before test started, or that EGR is flowing and ECM does not have ability to turn it off. The ECM tests EGR 6 times in a given key cycle. If EGR does not respond 3 or more times in 5 tests, code EO48 is set.

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

1. Many codes disable EGR and inhibit EO48 test. Repair other DFI codes before diagnosis of code EO48.
2. At idle, the EGR solenoid is electrically energized, blocking the flow of vacuum to the EGR valve.

Drive vehicle with TPS position between 8-15 degrees, and engine at 1450-1650 RPM to try and duplicate code. Remove EGR valve and check for excessive carbon build up that would restrict EGR flow, or foreign materials holding EGR valve open. Check for pinched, cut, kinked, misrouted or blocked vacuum passages and/or vacuum hoses, reducing EGR flow.

Flow Chart, Code EO48, EGR System Fault (1 Of 2). Scheme 269

Note. Perform "DFI System Check" before diagnosing Code EO48.

Flow Chart, Code EO48, EGR System Fault (1 Of 2). Scheme 270

ECM CODE EO48 - EGR SYSTEM FAULT (2 OF 2)

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

1. This step checks for power at EGR solenoid.
2. This steps checks the ECM's ability to command EGR on.

Drive vehicle with TPS position between 8-15 degrees, and engine at 1450-1650 RPM to try and duplicate code. Remove EGR valve and check for excessive carbon build up that would restrict EGR flow, or foreign materials holding EGR valve open. Check for pinched, cut, kinked, misrouted or blocked vacuum passages and/or vacuum hoses, reducing EGR flow.

Flow Chart, Code EO48, EGR System Fault (2 Of 2). Scheme 271

Flow Chart, Code EO48, EGR System Fault (2 Of 2). Scheme 272

Always tested.

ECM looks for all full time memory information to be erased or reset. If full time memory is completely erased, code EO52 is stored.

All block learn counts are reset to 128 counts and code EO52 is stored as a history code.

This code indicates that long-term memory in ECM has been reset. This will result whenever power is removed from ECM (i.e. disconnecting battery cables, disconnecting ECM connector, etc.). Code should be cleared from memory after restoring ECM's power supply.

If code EO52 is seen accompanied by complaint of engine quit, stumble, lights flashing or other stored codes, check for intermittent loss of power or ground to ECM on circuit Nos. 480 and 450. Manipulate wiring and connections with engine running. Unplug and plug ECM connectors to ensure that they are latched.

Schematic, Code EO52, ECM Memory Reset. Scheme 273

Engine speed above 448 RPM.

No distributor reference pulses for .7 seconds.

Code EO53 is stored as a history code. No diagnostic lights/service messages are illuminated.

Code EO53 is set if ECM does not receive distributor reference pulses from HEI for more than .7 seconds. Since DFI system requires HEI pulses in order to fire the injectors, most occurrences of code EO53 will be accompanied by a stall.

Code EO53 can be set by ignition switch contact timing when turning key off. If ignition 3 contacts that feed the HEI open before ignition 1 contacts, a code EO53 may be set. When code EO53 does not turn on any diagnostic lights/service messages, do not attempt to diagnose a history EO53 unless there are complaints of stumble, miss, stall or other driveability conditions that could be caused by loss of spark or fuel injection.

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

1. Check for hard failure of distributor reference which will cause code EO12 to set.
2. Do not diagnose code EO53 unless there are complaints of stumble, miss, stall or other driveability conditions that could be caused by loss of spark or fuel.
3. Checks for code EO53 to set due to ignition key cycling.
4. Code EO53 is set if ECM does not receive distributor reference pulses from HEI for more than .7 seconds.
5. See NOTES ON INTERMITTENTS.

DO NOT attempt to diagnose Code EO53 unless there are complaints of stumble, stall, miss or other driveability conditions that could be caused by loss of spark or fuel. Code EO53 can be caused by: loss of ground on circuit No. 453. Loss of distributor reference signal on circuit No. 430. Loss of battery power to "B+" terminal of distributor. Ignition switch contact timing.

Flow Chart, Code EO53, Distributor Signal Interrupt. Scheme 274

Flow Chart, Code EO53, Distributor Signal Interrupt. Scheme 275

Codes EO21, EO22, EO26, and EO27 clear. ECM tests for code EO55 with key off. With key off, the ISC will retract until throttle switch opens. The TPS value is read by ECM, and a correction factor is stored. If correction value is the same on 2 consecutive key off cycles, TPS setting is relearned.

If TPS correction needed is from -10 to -2.9 degrees or from 3 to 90 degrees, the TPS out-of-adjustment-flag is set.

At next key on, the ECM will see TPS out-of-adjustment-flag, and set code EO55 as current. No diagnostic light or service message will appear.

The TPS is self adjusting. With key off, the ECM executes a TPS learning routine. After turning key off, the ECM will retract ISC until the ISC throttle switch opens and throttle linkage is resting on the minimum air screw. At that time, the ECM stores the TPS value and calculates a correction.

If the same correction factor occurs on 2 consecutive key off cycles, the TPS is corrected to zero degrees using correction factor learned. If value needs correction by more than -2.9 degrees or +3.0 degrees, code EO55 will be stored in memory at next key on cycle. Parameter ED01 displays uncorrected TPS values.

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

1. This steps checks for TPS adjustment. ECM parameter ED01 displays uncorrected TPS so that it can be used to check TPS adjustment.
2. If this reading is obtained, TPS adjustment is okay.
3. If TPS adjustment is okay, ISC and throttle switch operation need to be thoroughly checked. The throttle linkage needs to be checked for proper operation, throttle, cruise and throttle valve cables not binding, proper throttle return spring operation, and throttle shaft and blades free to move.

Manipulate ISC wiring while observing ECM input EI72 and while observing ISC operation during ECM output EO07. Manipulate TPS wiring and connector while observing ECM parameter ED01 for jumps, skips, and/or intermittent behavior.

Check for TPS secured to throttle body (both screws tight). Cycle TPS through its full travel while observing parameter ED01 for erratic behavior. Check for proper part number TPS installed on vehicle. Unplug and plug the TPS, ISC and ECM connectors and ensure that they are latched properly.

Flow Chart, Code EO55, TPS Out Of Adjustment. Scheme 276

Note. If code EO21, EO26, EO27 or EO30 are logged as current or history, do not use this procedure. See code EO21, EO22, EO26, EO27 and EO30 procedures to diagnose.

Flow Chart, Code EO55, TPS Out Of Adjustment. Scheme 277

Codes E014 and EO15 not set. Vehicle speed at 10 MPH for 10 minutes.

Transmission temperature less than or equal to -39°C with coolant temperature greater than or equal to 50°C. Transmission temperature greater than or equal to 148°C with coolant temperature less than or equal to 50°C.

ECM turns on "ENGINE CONTROL SYSTEM" light. ECM commands BCM to display "SERVICE SOON" message on CCDIC panel. ECM substitutes 110°C for transmission temperature.

The transmission temperature sensor a variable thermistor that varies its resistance depending on temperature. The sensor is a 2-wire sensor with a reference signal coming from the ECM to sensor on pin "A" on circuit No. 520. and a sensor reference ground pin "B" of circuit No. 476.

As temperature of sensor increases, its resistance decreases. As sensor resistance decreases, the voltage signal from the ECM decreases due to less voltage drop across temperature sensor. High temperature will result in low signal voltage on circuit No. 520 and low temperature will result in a high voltage signal on circuit No. 520. The ECM uses transmission temperature information to vary Viscous Converter Clutch (VCC) application speeds. Code E059 will set when the ECM sees an excessively low voltage or excessively high VCC temperature when coolant is hot or cold, respectively.

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

1. VCC sensor circuit is shorted to ground.
2. VCC sensor circuit is open.

Manipulate Transmission connector, ECM connector, and wiring of circuit No. 520 while observing ECM parameter ED26. If fault is induced, the data value will jump from a normal reading to a low or high reading. If so, repair open or short in circuit No. 520.

Unplug and plug the ECM transmission connectors and ensure they are latched properly. If wiring and connectors are okay, substitute a known good sensor and retest.

Review snapshot data parameters stored with this code to verify failure. If failure is verified, check and repair intermittent wiring connections or sensor.

Flow Chart, Code EO59, VCC Temperature Sensor Circuit. Scheme 278

Flow Chart, Code EO59, VCC Temperature Sensor Circuit. Scheme 279

Cruise control enabled. Cruise control engaged.

Transmission in park or neutral.

Disengage cruise control. Code E060 will be set if cruise control is engaged and park/neutral switch is closed, indicating that transmission is in park or neutral.

If code EO60 is stored as an intermittent code, check operation of park/neutral switch input test. After selecting input EI74, manipulate affected wiring while observing switch status. If switch changes status while wiring is being manipulated, repair faulty wiring or connections. If no trouble is found, it's possible that code can be set by inadvertently placing transmission into neutral while cruise control is engaged.

Flow Chart, Code EO60, Cruise Control/Trans Not In Drive. Scheme 280

Flow Chart, Code EO60, Cruise Control/Trans Not In Drive. Scheme 281

Cruise control enabled. Cruise control engaged. Cruise control not in resume mode.

Vehicle speed 20 MPH higher or lower than set speed for .5 seconds.

Cruise control disengaged.

Code E063 will be set if vehicle speed is 20 MPH higher or lower than the vehicle set speed. This code is used as a type of safety valve to the cruise control system. System can be set under normal conditions if driver accelerates and goes over 20 MPH over set cruise speed.

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

1. This steps checks cruise control servo's ability to pull in and stay in.
2. This step checks to see if vacuum leak is due to brake release valve and/or circuit, or servo and/or vacuum source.
3. This step checks to see if vacuum leak is due to vacuum source or servo.
4. This steps checks to see if fault is due to intermittent or slow vacuum leak.
5. This steps checks to see if fault is servo or brake vacuum release circuit.

If code EO63 is setting intermittently make sure owner is not overrunning set speed in excess of 20 MPH. Check vacuum source and brake release vacuum lines for proper connections and/or leaks.

Schematic, Code EO63, Vehicle Speed/Set Speed Difference To High. Scheme 282

Flow Chart, Code EO63, Vehicle Speed/Set Speed Difference To High. Scheme 283

Flow Chart, Code EO63, Vehicle Speed/Set Speed Difference To High. Scheme 284

Cruise control enabled and engaged.

Vehicle speed increases more than 4 MPH in .25 second.

Cruise control disengaged.

Code E064 is designed to set if vehicle speed is increasing at an extremely rapid rate (wheelspin). It is a protective measure so that wheels will not be under cruise control when on ice.

1. Code EO64 sets when vehicle speed increases greater than 5 MPH in one second with cruise control engaged.
2. If code EO64 is set, cruise control will disengage and code EO64 will be set in memory. No diagnostic lights will illuminate.
3. Most cases of code EO64 being set are due to wheelspin in icy or wet pavement conditions.
4. If code EO64 is found and no other cruise control faults exists, clear codes and road test vehicle. If code EO64 sets without wheelspin occurring, see CHART C1 - ECM REPLACEMENT CHECK.

If code EO64 is stored as an intermittent code and customer complains of frequent loss of cruise control, drive vehicle while observing ECM data ED12 (vehicle speed). If speed display is erratic, check operation and integrity of vehicle speed sensor circuit.

Cruise control enabled.

Coolant temperature is 126°C or higher.

Cruise control disengaged.

Code EO65 is designed to protect the engine from overheating. The ECM monitors coolant temperature and will disable cruise control if coolant temperature rises above 126°C. Code EO65 will be stored by ECM to alert technician to the reason the cruise control became disabled.

If code EO65 is set, cruise control will disengage and code EO65 will be stored in memory. No diagnostic lights will illuminate. If code EO65 is accompanied by hard or intermittent code EO14, see ECM CODE EO14 - SHORTED COOLANT SENSOR CIRCUIT chart. If code EO65 is set, check engine cooling system for overheating.

If an intermittent code EO65 is stored, manipulate coolant sensor wiring while observing ECM data ED04 (coolant temperature). If parameter jumps to a high reading (greater than 126°C), repair fault in wiring or connections.

Cruise control enabled and engaged.

Engine RPM is greater than or equal to 4800 for .25 seconds.

Cruise control disengaged.

Code EO66 will set if engine RPM exceeds 4800 RPM. This may occur on slippery pavement, extended wide open throttle acceleration, or mechanical problems (transmission slipping). Under these conditions, code EO65 will be set and should be considered normal. Vehicle owner should be advised why the cruise control disengaged. Clear code and road test vehicle.

Always tested.

Set/coast or resume/acceleration signal present when cruise control "ON/OFF" switch is turned to the "ON" position or if "SET/COAST" and "RESUME/ACCEL" switches are on at the same time.

Cruise control disengaged for entire key cycle.

When cruise control "ON/OFF" switch is in the "ON" position, system voltage is available at one side of the normally open contacts of the "RESUME/ACCEL" and "SET/COAST" switches. If cruise control "ON/OFF" switch is in the "ON" position, with ignition on, system voltage is available to the "RESUME/ACCEL" and "SET/COAST" switches.

If switches are stuck or their signal wires to the ECM are shorted to voltage, the vehicle could begin cruise control operation. To prevent this, code EO67 will set and disable cruise control if signal voltage from "SET/COAST" switch (circuit No. 84) or "RESUME/ACCEL" switch (circuit No. 87) is high when cruise control "ON/OFF" switch is turned from "OFF" to "ON" position or when ignition is turned on and cruise control "ON/OFF" switch was left on. Cruise control will disable for one ignition cycle.

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

1. ECM inputs EI83 and EI84 display "SET/COAST" and "RESUME/ACCEL" switch status as "HI" or "LO" depending on voltage state at ECM. If one of these inputs stays "HI" when switches are cycled, that particular switch or signal wire is shorted to voltage.
2. This step checks to see if short circuit reading is due to switch or circuit.

If an intermittent code EO67 is being set, manipulate related wiring while observing ECM inputs EI83 and EI84. If failure is induced, reading will jump from "LO" to "HI" with the switch off (not depressed). This code can also be set by vehicle owner if the cruise "ON/OFF" switch is turned on, or the "ON/OFF" switch was left on when ignition is turned on and the owner was depressing either the "SET/COAST" or "RESUME/ACCEL" switches.

Review snapshot data parameters stored with this code to verify failure. If failure is verified, check and repair intermittent wiring connections or sensor.

Flow Chart, Code EO67, Cruise Control Switch Shorted. Scheme 285

Flow Chart, Code EO67, Cruise Control Switch Shorted. Scheme 286

ECM INPUT DATA CODE IDENTIFICATION

ECM INPUT DATA CODES

ECM INPUT CODE EI71 - VCC BRAKE SWITCH CIRCUIT

The Viscous Converter Clutch (VCC) brake switch is normally closed and opens when brake pedal is depressed. The VCC brake switch supplies power to VCC solenoid. To do so, brake switch receives 12 volts from a 15-amp "IGN 1" fuse on circuit No. 39, and sends the 12-volt signal to ECM and VCC solenoid on circuit No. 420. When brake is depressed, switch opens and circuit No. 420 voltage is read by ECM as zero volts.

A "HI" on diagnostic display, indicates that switch is closed (no braking) while a "LO" display indicates an open switch (brake pedal depressed). ECM uses VCC brake input to determine braking status for VCC apply and release, as well as a test condition for many codes.

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

1. With key on and no braking, circuit should have 12 volts on both sides of VCC brake switch. Test light to ground should light, if either pin on brake switch connector is backprobed.
2. Light on one side means that brake switch is open as if brake pedal were depressed.
3. Light on circuit No. 420 with pedal depressed means that brake switch never opens.
4. Unplug and plug ECM connector and ensure that it is latched.

Check brake switch for proper adjustment. Check for intermittent open between fuse No. 7 to brake switch and then from brake switch to ECM. If fuse No. 7 blows intermittently, check for short to ground in circuit Nos. 39 and 420.

ECM Input Code EI71, VCC Brake Switch Circuit. Scheme 287

ECM INPUT CODE EI72 - THROTTLE SWITCH CIRCUIT

The throttle switch is part of the Idle Speed Control (ISC) motor. Pin "B" of 4-pin connector on ISC is throttle switch or closed throttle input to ECM. The ISC throttle switch contacts are normally open and closed when throttle linkage contacts ISC plunger (closed throttle, ISC in control of idle speed).

The ECM sends a 5-volt signal to pin "B" of ISC motor on circuit No. 427. When throttle linkage rests on ISC plunger, the throttle switch contacts close, shorting ISC pin "B" to pin "A" on circuit No. 450 (ground). The 5-volt signal from ECM is grounded at closed throttle, resulting in zero volts at ECM pin "C10". When throttle is opened, the throttle switch opens pin "B" on circuit No. 427, resulting in 5 volts at ECM pin "C10".

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

1. With ISC plunger depressed, status should be "LO" (closed throttle). When plunger is released, status should be "HI" (open throttle).
2. Check throttle shaft for throttle plates binding, weak or distorted throttle spring, cruise and throttle valve cables for binding, throttle linkage, and check TPS for proper installation.
3. When ISC bottoms fully in retracted position, the throttle switch will open. ISC should be partially extended to control idle.
4. Never connect voltage source across pins "A" and "B" of ISC. Damage to throttle switch contacts will result.
5. This step simulates the throttle switch shorting pin "A" to pin "B". If removing and replacing jumper causes switch to cycle, harness and ECM are okay. Fault is in ISC motor connector or ISC motor.
6. This steps checks for 5-volt reference signal to ISC.
7. A 5-volt reference from ECM to ISC is open or shorted to ground.
8. A 5-volt reference is okay, when checking for open circuit No. 450F from ISC pin "B" to ground.

Check for binding throttle linkage due to throttle valve, cruise control or throttle cables, TPS installed improperly, or throttle shaft binding. Check for proper throttle return spring and throttle return spring installation.

Probe ECM pin "C10" to ground with a voltmeter. Manipulate wiring and connectors at closed throttle and watch for 5 volts, indicating an open from pin "C10" to ground. Manipulate wiring and connectors at open throttle and watch for zero volts, indicating short to ground on circuit No. 427.

ECM Input Code EI72, Throttle Switch Circuit. Scheme 288

ECM INPUT CODE EI74 - PARK/NEUTRAL SWITCH CIRCUIT

The park/neutral switch is a part of transmission gear selector switch. Pin "A" of 6-pin connector on switch is park/neutral input for ECM and BCM. The park/neutral switch contacts are closed in park or neutral, shorting switch pin "A" to ground. In any other gear range, pin "A" is open.

The ECM sends 12 volts to pin "A" of gear selector switch over circuit No. 434. When gear selector is in park or neutral, the 12-volt signal from ECM is shorted to ground resulting in zero volts at ECM pin "A4". In reverse or forward gears, circuit No. 434 is open to ground resulting in 12 volts at ECM pin "A4".

A "HI" status on diagnostic display indicates that switch is open (not in park or neutral), a "LO" status indicates a closed switch (gear selector in park or neutral). The ECM uses park/neutral status for fuel and idle speed control, and as a test condition for many trouble codes.

Check for NSBU switch and transmission indicator out of adjustment. Check for open or short to ground in circuit No. 434 between ECM and switch. Check for open to ground on switch pin "B".

Review snapshot data parameters stored with this code to verify failure condition. If failure condition is verified, check and repair intermittent wiring connections or sensor.

ECM Input Code EI74, Park/Neutral Switch Circuit. Scheme 289

ECM INPUT CODE EI78 - POWER STEERING PRESSURE SWITCH CIRCUIT

The power steering switch is normally closed and opens with high power steering pressure. During normal driving, the power steering switch receives 12 volts from the 10-amp ECS fuse over circuit No. 639B, and sends the 12-volt signal to ECM on circuit No. 495. When high power steering pressures occur, the switch opens and circuit No. 495 voltage is read by ECM as zero volts.

The ECM uses power steering input to extend the ISC motor when high power steering pressures occurs at low speeds, such as parking maneuvers.

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

1. Input test EI78 must be performed with engine running.
2. Status "STAYS HI" means that switch is not opening with high pressure or that circuit No. 495 is shorted to voltage.
3. Status "STAYS LO" means that ECM never receives a 12-volt signal on circuit No. 495.
4. Unplug and plug ECM connector and ensure it is latched properly.

With key on, engine off, manipulate wiring and connectors while observing ECM Input EI78. If EI78 cycles to "LO" at any time, repair intermittent open.

Review snapshot data parameters stored with this code to verify failure. If failure is verified, check and repair intermittent wiring connections or sensor.

ECM Input Code EI78, Power Steering Pressure Switch Circuit. Scheme 290

ECM INPUT CODE EI79 - CRUISE CONTROL ENABLE ON/OFF INPUT

The cruise control enable switch provides power to the cruise enable input of the ECM. The ECM cannot allow cruise control operation until the enable or instrument panel switch is turned to the "ON" position, which passes 12 volts to ECM pin "C12".

The Amber cruise "ON" indicator can be used to monitor cruise control switch status. Turn cruise control switch on and manipulate wiring and connectors. If switch or circuit from fuse to switch are open, the Amber indicator light will go out.

If the cruise control 3-amp fuse blows intermittently, turn cruise control switch on, manipulate wiring, connectors, and cruise control/steering column switch. If circuit becomes grounded, the fuse will blow.

ECM Input Code EI79, Cruise Control Enable On/Off Input. Scheme 291

ECM INPUT CODE EI80 - CRUISE CONTROL SET/COAST INPUT

Cruise control "SET/COAST" switch is normally open, providing a 12-volt signal to ECM pin "B4" when switch is depressed. When cruise control dash switch is depressed to "ON" position, the dash switch provides a 12-volt signal to the cruise control/steering column switch on pin "A4" of circuit No. 397. When "SET/COAST" button is depressed, the steering column switch pin "A4" is connected to pin "E3" of circuit No. 84, providing the ECM with a 12 volt input on pin "B4".

To diagnose intermittent set/coast function, turn cruise control dash switch to "ON" position and backprobe ECM pin "B4" with a voltmeter to ground. Pin "B4" should show 12 volts with "SET/COAST" switch depressed and zero volts with "SET/COAST" switch released. Cycle switch while manipulating wiring and connectors.

ECM Input Code EI80, Cruise Control Set/Coast Input. Scheme 292

ECM INPUT CODE EI81 - CRUISE CONTROL RESUME/ACCEL INPUT

The ECM cruise control "RESUME/ACCEL" switch is normally open and provides a 12-volt signal to ECM over pin "B6" when depressed. When cruise control dash switch is depressed to "ON" position, the dash switch provides a 12-volt signal to the cruise control/steering column switch over pin "A4" of circuit No. 397. When "RESUME/ACCEL" button is depressed, the steering column switch pin "A4" is connected to pin "C" of circuit No. 87, providing the ECM with a 12 volt resume/accel input on terminal "B6".

To diagnose an intermittent resume/accel function, turn cruise control dash switch to "ON" position and backprobe ECM pin "B6" with a voltmeter to ground. Terminal "B6" should show 12 volts with turn cruise dash switch to "ON" position and backprobe ECM pin "B4" with a voltmeter to ground. Terminal "B6" should show 12 volts with "RESUME/ACCEL" switch depressed and zero volts with "RESUME/ACCEL" switch released. Cycle switch while manipulating wiring and connectors.

Input Code EI81, Cruise Control Resume/Acceleration Input. Scheme 293

DFI Fuel System/ECM Wiring Diagram. Scheme 294