Dfi Tests W/codes Cadillac Fleetwood 75 Series

DIAGNOSIS & TESTING

The ECM stores component failure information for DFI system under a related trouble code which can be recalled for diagnosis and repair. When recalled, these codes will be displayed on Electrical Climate Control (ECC) panel starting with lowest numbered code. Only codes in which a related malfunction has occurred will be displayed. When system is displaying in diagnostic mode, Fuel Data Display panel will show no readings.

Note. The terms "enter diagnostics" and "exit diagnostics" will be used periodically throughout this section. Follow the procedure for entering diagnostic mode when instructed to "enter diagnostics". Follow the procedure for exiting diagnostic mode when instructed to "exit diagnostics".

ENTERING DIAGNOSTIC MODE

Turn ignition on. Depress "OFF" and "WARMER" buttons on ECC panel simultaneously and hold buttons until ".." appears on digital display panel. Release buttons and code "-1.8.8" should appear, indicating beginning of diagnostic readout. Trouble codes will be displayed beginning with lowest numbered code and be repeated a second time. After second time, trouble code ".7.0" will appear, indicating ECM is ready for next diagnostic feature. If no codes are stored, 1.8.8" will appear for longer period of time, then code ".7.0" will appear. (Scheme 50)

Note. Trouble code ".7.0" is a decision point. When this code is displayed, either select diagnostic feature e.g., switch test, engine data display, etc., or clear codes and then exit diagnostic mode.

Trouble Code "-1.8.8" Displayed on Electronic Climate Control (ECC) Panel. Scheme 50

CLEARING TROUBLE CODES

Trouble codes stored in ECM memory may be cleared (erased) by entering diagnostic mode and then depressing "OFF" and "HI" buttons at the same time. Hold buttons until ".0.0" is displayed. Release buttons and code ".7.0" should appear.

EXITING DIAGNOSTIC MODE

Depress any ECC function keys except "LO" or "OUTSIDE TEMP". Exiting may also be completed by turning ignition off for 10 seconds. This will take ECC panel out of diagnostic mode, but will not clear any trouble codes. Original temperature setting should appear on ECC panel.

ENGINE MALFUNCTION TEST PROCEDURE

During any diagnostic procedure, "hard failure" codes MUST be distinguished from "intermittent failure" codes. Diagnostic charts CANNOT be used to analyze "intermittent failure" codes, except as noted under Diagnostic Procedure. To determine "hard failure" codes and "intermittent failure" codes, proceed as follows

1) Enter diagnostics. ECC will display trouble codes beginning with lowest numbered code. Each code will be displayed for 2 seconds until the highest code present has been displayed. Record all codes. Then, "-1.8.8" will appear.

2) Display procedure will repeat twice. On the third pass through the display, "hard failure" codes ONLY, will be displayed. Record all codes again. Any codes which appeared during the 1st and 2nd passes but not during the 3rd, are "intermittent failures". If no codes are displayed during the 3rd pass, there are no "hard failures", and the "CHECK ENGINE" light should have been out before entering diagnostics.

3) The 3rd pass ends with "-1.8.8" display. When trouble code sequence is completed, ".7.0" will display. If a code "51" is present, it must be diagnosed before further testing can begin. As long as "51" is displayed, no other diagnostic features are possible.

4) Begin diagnosis with the lowest numbered code, unless codes "51" and/or "16" are present. If codes "51" or "16" are shown, begin diagnosis with code "51", then proceed to code "16" since these codes may have an effect on setting of other codes. If no trouble codes are present, ECC will display "-1.8.8" for 2 seconds and then ".7.0".

Note. If vehicle exhibits performance problems and no codes are set, refer to the performance charts. Components recorded by trouble codes generally do not cause performance problems when no codes are stored.

1. If "intermittent failures" "13", "20", "33", "39", "44" or "45" appear, use diagnostic chart for corresponding "hard failure" code.

TROUBLE CODE ID CHART

1983 PROGRAMMED ECM TROUBLE CODES

Note. After diagnosing trouble codes; switch tests, engine data displays and output cycling tests can be used to isolate "intermittent failures". DO NOT perform any adjustment or repairs on any component until malfunction has been positively located.

Scheme 51

1. Enter diagnostics and with code ".7.0" displayed, depress and release brake pedal. This will start switch test procedure and code ".7.1" will be displayed. NOTE: Each test action must be performed within 10 seconds after codes appear on display panel or ECM will store code as failure and proceed to next code.
2. With code ".7.1" displayed, depress and release brake pedal again. Code ".7.2" should appear. With code ".7.2" displayed, depress throttle to wide open position and release. Code ".7.3" should appear.
3. With code ".7.3" displayed, shift transmission into drive then back to neutral. Code ".7.4" should appear. With code ".7.4" displayed, shift transmission to reverse and back to park. Code ".7.5" should appear.
4. With code ".7.5" displayed, switch cruise control on then off. Code ".7.6" should appear. With code ".7.6" displayed, switch cruise control on, then depress and release "Set/Coast" button. Code ".7.7" should appear. With code ".7.7" displayed, switch cruise control on, then depress and release "Resume/Acceleration" switch. Code ".7.8" should appear. NOTE: To pass codes ".7.5", ".7.6" and ".7.7" on vehicles without cruise control, allow codes to appear for 10 seconds each, then proceed with step 5). Codes will cycle through ECM and be processed as failures.
5. With code ".7.8" displayed, depress and release "Instant/Average" button on Fuel Data panel. Code ".7.9" should appear. With code ".7.9" displayed, depress and release "Reset" button. Code ".8.0" should appear. (Scheme 51): View of Fuel Data Panel
6. With code ".8.0" displayed, push "Outside Temp" button twice. This test checks ECM's ability to recognize and process air conditioning clutch signal. This test may require engine running with A/C operating in "Auto" mode with temperature selection set at 60°F (16°C). NOTE: To pass code ".8.0" on vehicles without rear window defogger, momentarily supply 12 volts to Blue wire in 6-wire connector on ECC power module while code ".8.0" is displayed.
7. When switch tests are completed, ECM will display codes which did not pass test. Each code will appear beginning with lowest code. Codes will not disappear until affected switch circuit is repaired and retested. After switch tests are completed, ECC will display code ".0.0" and return to code ".7.0". Code ".0.0" indicates all switch circuits are operating properly. Remember that ".0.0" will never be obtained on vehicles without cruise control.

ENGINE DATA DISPLAY PROCEDURE

1. Enter diagnostics and with code ".7.0" displayed, press "Reset" button on Fuel Data panel. Code ".9.0" should appear. If code ".9.0" does not appear, refer to switch test code ".7.9". NOTE: To advance to code ".9.0" on vehicles without cruise control, momentarily jumper Yellow wire (Pin C, Circuit No. 904) and Lt. Blue/Black wire (Pin D, Circuit No. 903) in 6-wire cruise control instrument panel switch connector. Connector is located on left side of steering column under instrument panel.
2. Engine data display shows values of 13 parameters monitored by ECM. Parameter numbers .0.1-.1.3 will be displayed for 1 second on ECC panel, followed by a numerical value. The parameter value will be displayed for 9 seconds. Each parameter and value will be repeated until manually advanced to next parameter.
3. To advance display, depress "Instant/Average" button on Fuel Data panel. To return to previously displayed parameter, depress "Reset" button. After last parameter is displayed, code ".9.5" should appear. Engine data display may be cleared at anytime, by pressing "Off" and "High" buttons on ECC panel simultaneously. Code ".7.0" should appear.
4. Engine data display information can be used to compare information of engine to that of properly functioning engine for diagnosis of malfunctions. Parameters read and values displayed are as follows

ENGINE DATA PARAMETERS

ENGINE DATA PARAMETERS EXPLANATION

OUTPUT CYCLING TESTS PROCEDURE

1. Enter diagnostics and with code ".7.0" displayed on ECC panel, depress "Instant/Average" button on Fuel Data panel. If code ".9.5" does not appear, refer to switch test code ".7.8". Depress "Instant/Average" button of Engine Data Display. Parameter ".1.3" should appear.
2. The output cycling test turns ECM's outputs on and off. To enter actuator cycling tests, start engine. Turn engine off and within 2 seconds, turn ignition on. Enter diagnostics and display code ".9.5" on ECC panel. Depress accelerator pedal to wide open throttle position and release pedal. Code ".9.6" should appear. If ".9.6" does not appear, refer to switch test ".7.2".
3. Turn cruise instrument panel switch on. Cruise control outputs will cycle. Output cycling tests will automatically end after 2 minutes. After cycling output is complete, display should switch from code ".9.6" back to code ".9.5". Additional output cycling may be obtained by pressing and releasing the throttle switch.

FIXED SPARK MODE PROCEDURE

1. Purpose of test is to verify proper adjustment of spark timing. Enter diagnostics and with code ".7.0" displayed on ECC panel, depress "Instant/Average" button on Fuel Data panel. Code ".9.5" should appear.
2. With engine at normal operating temperature, idling at less than 900 RPM and transmission in "P" position, attach a timing light and observe ignition timing. Under these conditions, and with HEI operating properly (codes 23 and 25 not set), ignition timing should be within 18-22° BTDC. If not, the base timing of 10° BTDC should be adjusted accordingly.

PERFORMANCE CHART MENU

SYMPTOM-TO-PERFORMANCE CHART MENU

Diagnostic Aids

The following conditions 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 the individual codes.

Flow Chart - Multiple Trouble Codes Store Hard. Scheme 52

A-1 CONDITION: CODES 22, 32 AND 36 ALL STORED HARD

Cause: Loss Of "5 Volt Reference" Voltage To Sensors

Flow Chart - Multiple Trouble Codes Store Hard. Scheme 53

If Codes 22, 32 and 36 are all stored hard, this is probably caused by the loss of 5 volts on circuit 474 (5 volt reference). To verify this condition, probe the following harness terminals with a voltmeter to ground

1. MAP sensor harness connector Pin C
2. BARO sensor harness connector Pin C
3. TPS sensor harness connector Pin C

If the voltage is 0 for the three sensors, circuit 474 must be investigated for an open or short to ground. If a defect is not found in the wiring, either the ECM connector or ECM itself is faulty. If the proper 5 volt signal is observed on any of the three sensor terminals then the diagnostic procedures for each individual code must be followed.

A-2 CONDITION: CODE 15 STORED HARD ALONG WITH HARD CODE 21, 26 OR 33

Cause: Open In "Sensor Ground" To Sensors

A-2 Condition: Code 15 Stored Hard Along With Hard Code 21, 26 OR 33. Scheme 54

If a code 15 is stored hard along with a hard Code 21, 26 or 33 this is probably caused by an open in the sensor ground circuit 476-X. To verify this condition, probe the following harness terminals with a voltmeter to 12 volts

1. Coolant Temp sensor outer harness terminal
2. TPS sensor harness connector Pin B
3. BARO sensor harness Pin A

If the voltage is 0 for the three sensors, circuit 476-X must be investigated for an open. If a defect is not found in the wiring, either the ECM connector or ECM itself is faulty. If 12 volts observed for any of the three sensors, then the diagnostic procedures for each individual code must be followed.

A-3 CONDITION: CODE 38 STORED HARD ALONG WITH HARD CODE 33, 34 OR A VERY LOW OUTSIDE TEMPERATURE DISPLAY

Cause: Open In "Sensor Ground" To Sensors

A-3 Condition: Code 38 Stored Hard Along With Hard Code 33, 34 Or a Very Low Ootside Temperature Display. Scheme 55

If a Code 38 is stored hard along with a hard Code 33, 34 or a very low outside temperature display, this is probably caused by an open in the sensor ground circuit 476-Y. To verify this condition, probe the following harness terminals with a voltmeter to 12 volts

1. MAT sensor outer harness terminal
2. MAP sensor harness Pin A
3. Outside Temp sensor harness Pin A

If the voltage is 0 for the three sensors, circuit 476-Y must be investigated for an open. If a defect is not found in the wiring, either the ECM connector or ECM itself is faulty. If 12 volts is observed for any of three sensors then the diagnostic procedures for each individual code must be followed.

Flow Chart, Code 12 - No Distributor (Tach) Signal. Scheme 56

Flow Chart, Code 12 - No Distributor (Tach) Signal. Scheme 57

Note. If this code IS NOT displayed during the third pass of diagnostic codes, it is an intermittent failure and cannot be diagnosed using this procedure. For an intermittent code, refer to NOTE ON INTERMITTENTS.

This code is set during cranking and results in a condition where the engine will not start. Trouble Code 12 indicates that the distributor spark timing reference pulses, which are generated by the pickup coil, are not being received by the ECM. The possible causes are

1. A. No reference pulses generated by the HEI system.
2. B. Defective wires, terminals, etc.
3. C. The ECM not processing the signal properly.

1. Check for HEI reference pulses by disconnecting the 4-way weatherpack connector at the distributor and measuring the voltage between the distributor connector pin B and ground. Crank the engine. Voltage on pin B should be between 0.5 and 2.0 volts. If the voltage is less than 0.5 volts or greater than 2.0 volts, the HEI system should be checked with an HEI tester (part no. ST-125). If no spark occurs during crank, refer to HEI DIAGNOSIS in BASIC TESTING article. If spark does occur, then the problem is in the distributor harness or HEI module itself.
2. A voltage of 0.5 to 2.0 volts at pin B indicates that the distributor spark timing reference pulses are present. Reconnect the distributor connector. The reference pulses are carried through circuit 430 to the ECM. Check circuit 430 for an open or short to ground. Disconnect the ECM and crank engine. Measure the voltage on circuit 430 while cranking. If the reading is less than 0.5 volts, the wire is either open or shorted to ground. A reading of 0.5 to 2.0 volts indicates that the wire is OK, check circuit 453 for an open. If circuit 453 is OK, check for a faulty ECM connector or faulty ECM. A voltage greater than 2.0 volts on pin Z indicates that circuit 430 is shorted to voltage.

Note On Intermittents

If an intermittent Code 12 is being set, observe engine performance while manipulating the related wiring. Since Code 12 is a "no-start" condition, when the failure is induced, the engine should begin to stall. This will help to isolate the location of the malfunction.

If the crank signal circuit (circuit 6) is shorted to voltage at the ECM, the ECM will begin checking for distributor pulses and set Code 12 if the engine is not turning. As soon as the engine starts, Code 12 will become intermittent, however both "Service" telltale lights will remain on since the ECM thinks the engine is still cranking.

Flow Chart, Code 13 - Oxygen (O2) Sensor Not Ready. Scheme 58

Flow Chart, Code 13 - Oxygen (O2) Sensor Not Ready. Scheme 59

Note. The following procedure is designed to account for intermittent codes. If no malfunction is uncovered using this procedure, it will indicate that the DFI system is OK at this time. Refer to NOTE ON INTERMITTENTS.

When the oxygen sensor is warm (above 200°C), the output voltage will swing between 0 and 1.0 volts. Code 13 indicates that the oxygen sensor will not swing above or below its cold voltage of approximately 0.5 volts and that the system will not go to closed loop operation. Possible causes are

1. A. The oxygen sensor not functioning properly.
2. B. Defective wires, terminals, etc.
3. C. The ECM not processing the signal properly.

1. To check the operation of the oxygen sensor, observe engine data parameter .0.7 with the oxygen sensor disconnected. If the oxygen sensor voltage is less than .37 or greater than .57, the wiring harness must be investigated for defects. If the wiring is OK, then the ECM connector and ECM must be checked because the system is not functioning properly.
2. If the voltage is between .37 and .57 volts, then jumper the oxygen sensor harness pins together (ECM side) and note the voltage reading. If the voltage reading is greater than .05 volts, then the ECM is not able to recognize that a fault was artificially created. Therefore, either the ECM is not functioning properly or an oxygen sensor circuit is open between the connector and the ECM.
3. If the voltage reading is less than .05 volts, then the ECM is functioning properly and the harness is OK. The oxygen sensor should be checked using the procedure in «CHART 14 - O2 SENSOR TEST»(/cadillac/fleetwood/75-series-1956-1992/remont/testing-diagnostics/#dfi-tests-wcodes) .

If an intermittent Code 13 is being set, manipulate the related wiring while observing engine data parameter .0.7 at part throttle with the engine warm, ("open/closed loop" status light should be on). If the failure is induced, the "oxygen sensor" reading will change from its normal fluctuating voltage (above .60 and below .30) to a fixed value around .50 volts. This will help to isolate the location of the malfunction.

Flow Chart, Code 14 - Shorted Coolant Temperature (CTS) Sensor Circuit. Scheme 60

Flow Chart, Code 14 - Shorted Coolant Temperature (CTS) Sensor Circuit. Scheme 61

Note. If this code IS NOT displayed during the third pass of diagnostic codes, it is an intermittent failure and cannot be diagnosed using this procedure. For an intermittent code, refer to NOTE ON INTERMITTENTS.

Trouble Code 14 indicates that the coolant sensor signal voltage is too low. This condition will be observed in engine data display as a "coolant temperature" reading (parameter .0.4) of 142°-151°C. Possible causes of this condition are

1. A. A shorted coolant sensor.
2. B. Defective wiring, terminals, etc.
3. C. ECM not processing the coolant signal properly.

1. If the opposite failure mode (open sensor) is created, then the self-diagnostics can be used to detect this failure by displaying engine data parameter .0.4. With the opposite failure created, parameter .0.4 should display a "coolant temperature" reading of -40° to -35°C. To create an open sensor signal, disconnect the coolant sensor connector. If the "coolant temperature" reading is now -40° to -35°C the ECM and the wiring harness are OK. The fault must be in the coolant sensor itself. If the "coolant temperature" reading is -34°C or greater, then there is a short to ground in the wiring harness or the ECM.

If an intermittent Code 15 is being set, manipulate the related wiring while observing engine data parameter .0.4. If the failure is induced, the "coolant temperature" reading will jump from its normal value to the "shorted" reading of 142° to 151°C. This will help to isolate the location of the malfunction.

Flow Chart, Code 15 - Open Coolant Temperature Sensor (CTS) Circuit. Scheme 62

Flow Chart, Code 15 - Open Coolant Temperature Sensor (CTS) Circuit. Scheme 63

Note. If this code IS NOT displayed during the third pass of diagnostic codes, it is an intermittent failure and cannot be diagnosed using this procedure. For an intermittent code, refer to NOTE ON INTERMITTENTS.

Trouble Code 15 indicates that the coolant sensor signal voltage is too high. This condition will be observed in engine data display as a "coolant temperature" reading (parameter .0.4) of -40° to -35°C. Possible causes of this condition are

1. A. An open coolant sensor.
2. B. Defective wiring, terminals, etc.
3. C. An ECM not processing the coolant signal properly.

1. If the opposite failure mode (shorted sensor) is created, then the self-diagnostics can be used to detect this failure by displaying engine data parameter .0.4. With the opposite failure created, parameter .0.4 should display a "coolant temperature" reading of 148° to 151°C. To create a shorted sensor signal, disconnect the coolant sensor and jumper the harness terminals together. If the "coolant temperature" reading is 148° to 151°C, the ECM and the wiring harness are OK. The fault must be in the sensor connector or coolant sensor itself.
2. If the "coolant temperature" reading is 147°C or less, then there is an open in the signal circuit 410, in the sensor ground circuit 476-X, or in the ECM. If the "coolant temperature" reading is now 148° to 151°C with circuit 410 jumpered to ground, an open exists in circuit 476-X.
3. If the "coolant temperature" reading remains 147°C or less with circuit 410 jumpered to ground at the ECM, either the ECM connector or ECM itself is faulty. If the reading is now 148° to 151°C an open exists in circuit 410.

If an intermittent Code 15 is being set, manipulate related wiring while observing engine data parameter .0.4. If the failure is induced, the "coolant temperature" reading will drop from its normal value to the "open" reading of -40° to -35°C. This will help to isolate the location of the malfunction.

Flow Chart, Code 16 - Alternator Voltage Out of Range. Scheme 64

Flow Chart, Code 16 - Alternator Voltage Out of Range. Scheme 65

Note. If this code IS NOT displayed during the third pass of diagnostic codes, it is an intermittent failure and cannot be diagnosed using this procedure. For an intermittent code, refer to NOTE ON INTERMITTENTS.

Code 16 indicates that the generator output voltage is either above or below specification with the engine running. The ECM monitors the generator voltage indirectly by checking the voltage on the fuel pump feedback input (circuit 120).

1. With the engine running, check the voltage on the fuel pump fuse. If the voltage is between 10.5 and 15.5 volts, then the ECM connector or ECM itself is at fault. If the voltage is less than 10.5 volts or greater than 15.5 volts with the engine running, then refer to generator diagnosis in Alternator article because the generator circuitry is operating improperly.

If an intermittent Code 16 is being set, observe engine data parameter .1.0. This "battery voltage" reading is monitored off the fuel pump feedback input (circuit 120) which is also used to set Code 16. If the Code is being set due to high current draw in a certain vehicle component, this effect can be observed reading parameter .1.0. Operate the various components while watching for the reading to drop below 10.5 volts. This will help to isolate the location of the malfunction.

Flow Chart, Code 18 - Open Crank Signal Circuit. Scheme 66

Flow Chart, Code 18 - Open Crank Signal Circuit. Scheme 67

Note. If this code IS NOT displayed during the third pass of diagnostic codes, it is an intermittent failure and cannot be diagnosed using this procedure.

While the engine is cranking, a 12 volt signal will be present in the cranking circuit from the ignition switch to the ECM.

A Code 18 indicates that the 12 volt signal is not present at the ECM while the engine is cranking. Possible causes of this condition are

1. A. An open 3 amp crank fuse.
2. B. Defective wiring, terminals, etc.
3. C. An ECM not processing the signal properly.

1. Check the 3 amp crank fuse. If it is b]own, check circuit 6 for a short to ground between the fuse and the ECM. If this circuit is OK and the fuse blows again then the short must be in the ECM connector or ECM itself.
2. If the fuse is OK, check the voltage at the crank fuse while cranking the engine. If the voltage is 0 volts, then an open exists in circuit 6 between the fuse and the ignition switch.
3. If the fuse has 12 volts on it, then check for voltage on circuit 6 at the ECM while cranking the engine. If 12 volts is measured, then check the pin K terminal for an open before replacing the ECM. If no voltage is measured at the ECM, then repair the open in circuit 6 between the fuse and the ECM.

Flow Chart, Code 19 - Shorted Fuel Pump Circuit. Scheme 68

Flow Chart, Code 19 - Shorted Fuel Pump Circuit. Scheme 69

Note. If this code IS NOT displayed during the third pass of diagnostic codes, it is an intermittent failure and cannot be diagnosed using this procedure. For an intermittent code, refer to NOTE ON INTERMITTENTS.

When the ignition is turned on, the ECM energizes the fuel pump relay for 2 seconds which feeds 12 volts to the fuel pump circuit (120). Unless distributor reference pulses are received within this time, the ECM will de-energize the relay so that the fuel pump does not continue to run at ignition on.

Trouble Code 19 indicates that the fuel pump relay circuit continues to have 12 volts on it after the 2 second fuel pressure prime. This voltage is read by the ECM on the fuel pump feedback input (circuit 120). This is also the voltage which is displayed on Engine Data Parameter .1.0. Under the conditions of a Code 19, the "battery voltage" reading will be greater than 11 volts at ignition on (parameter .1.0 reading is normally 0 volts at ignition on). Possible causes of this condition are

1. A. A faulty fuel pump relay.
2. B. A faulty oil pressure switch.
3. C. Defective wiring, terminals, etc.
4. D. An ECM not processing the fuel pump feedback voltage properly or not switching the relay off.

1. If the unwanted source of voltage can be eliminated, then self-diagnostics can be used to detect this by displaying engine data parameter .1.0. When the voltage is removed from the circuit, the "battery voltage" reading will drop to 0 volts. Begin eliminating branches of the fuel pump circuit by removing the oil pressure switch connector. If the "battery voltage" reading is now 0, then the oil pressure switch must be replaced because it is closing the switch without receiving oil pressure.
2. If the "battery voltage" reading is still greater than 0 volts, another portion of the fuel pump circuit can be eliminated by removing the fuel pump relay. If the "battery voltage" reading is still greater than 0 volts, then circuit 120 and 120E must be inspected for a short to voltage. If the voltage on circuit 120 is greater than 0 volts with the ECM disconnected, the circuit is shorted to voltage. If the voltage is 0, the fault must be in the ECM connector or ECM itself.
3. If the "battery voltage" reading is now 0 after removing the fuel pump relay, probe relay socket cavity 5 with a test light to ground. After turning ignition on, the test light should light for 2 seconds and then go out. If the light does go out, replace the relay because it is failing to open.
4. If the test light stays on, then either the ECM or the wiring harness is shorted to voltage. If there is voltage on circuit 465 with the ECM disconnected, the circuit is shorted to voltage. If the voltage is 0, check for a faulty ECM connector or faulty ECM.

If an intermittent Code 19 is being set, manipulate the related wiring while observing engine data parameter .1.0 at ignition on. If the failure is induced, the "battery voltage" reading will jump from its normal 0 volt reading to a reading greater than 11 volts. This will help to isolate the location of the malfunction.

Flow Chart, Code 20 (1 of 2) - Open Fuel Pump Circuit. Scheme 70

Flow Chart, Code 20 (1 of 2) - Open Fuel Pump Circuit. Scheme 71

Flow Chart, Code 20 (2 of 2) - Fuse Blown. Scheme 72

Flow Chart, Code 20 (2 of 2) - Fuse Blown. Scheme 73

Note. The following procedure is designed to account for intermittent codes. If no malfunction is uncovered using this procedure, it will indicate that the DFI system is OK at this time. Refer to NOTE ON INTERMITTENTS if further investigation is necessary.

When the ignition is turned on, the ECM energizes the fuel pump relay for 2 seconds which feeds 12 volts to the fuel pump (circuit 120). As soon as distributor reference pulses are received, the ECM energizes the fuel pump relay so that the fuel pump circuit is fed 12 volts while the engine 15 running.

Trouble Code 20 indicates that the fuel pump relay circuit did not supply 12 volts to the fuel pump. Possible causes of this condition are

1. A. Faulty fuel pump relay.
2. B. Defective wiring, terminals, etc.
3. C. An ECM not processing the fuel pump signal or not switching the fuel pump relay on.
4. D. A shorted fuel pump.

1. To determine if the Code 20 is hard or intermittent turn the ignition off for 10 seconds to power down the ECM. Turn the ignition on for 5 seconds and then attempt to start the engine. If the engine now starts but Code 20 is not stored hard, then the malfunction is not present at this time. If the engine will not start, check the fuel pump fuse. If the engine starts with a hard Code 20 stored, it must then be determined if the ECM is receiving the proper feedback signal. If the "battery voltage" (parameter .1.0) reads 0 volts then check circuit 120 leading to the ECM for an open. If circuit 120 is OK, check for a faulty ECM connector or faulty ECM.
2. If the engine wil1 not run and the fuel pump is OK, or if the engine starts and parameter .1.0 reads battery voltage, the next step is to verify if the ECM is supplying a signal to the fuel pump relay. If the test light on circuit 465 does not light, reinstall the fuel pump relay and then check the circuit for an open or short to ground. If circuit 465 is OK, check for a faulty ECM connector or faulty ECM. If a short to ground is discovered, it must be repaired and then circuit 465 should again be checked for the proper signal. The short to ground could have damaged the ECM.
3. If the test light on circuit 465 does light for 2 seconds then the ECM is supplying the proper signal to energize the fuel pump relay. If the test light on circuit 120F does not light, an open must exist in circuits 120F or 3.
4. If the test light on circuit 120F does light, then the fuel pump relay is receiving 12 volts. Now determine if the relay is receiving a good ground from the ECM through circuit 497. If the test light between circuits 120F and 497 will not light with ignition on, then check circuit 497 for an open between the ECM and the relay. If circuit 497 is OK, check for a faulty ECM connector or faulty ECM.
5. If the test light does light, then we have a good ground. Check for continuity in circuit 120E. If the test light between circuits, 120F and 120E will not light with ignition on, then circuit 120E must be repaired for an open. If the test lights, then the fuel pump relay is failing to close and should be replaced.
6. If the fuel pump fuse is blown, it will be necessary to determine the cause of the excessive current draw. Battery voltage parameter .1.0 of the engine data series uses the fuel pump feedback signal as its source of voltage. With voltage applied to circuit 120E through the test light, a 0 voltage reading on the diagnostic display would indicate a short to ground in the system. If the display reads 0 volt, disconnect the 6-way weatherpack connector at the fuel tank and note the parameter value.
7. If the display reads 0 a short stil1 exists. If a voltage is displayed after removing the oil pressure switch connector, the switch must be shorted and should be replaced. If it remains at a 0 volt reading, the short is in either circuit 120 or 120E.
8. If the display now reads more than 0 volt, check the wiring between the 6-way weatherpack connector and the fuel pump for a short to ground. If the wiring is OK, the fuel pump must be inspected for a short to ground.
9. If the display of parameter .1.0 did not read 0 volt at the beginning of the procedure, then the short to ground is either in the fuel pump relay, the oil pressure switch or the wiring harness. If the test light on circuit 120F does not light, the fuel pump relay must be shorting to ground and should be replaced. If the test light does light, the short still exists. If the light goes out after removing the oil pressure switch connector the switch is shorted and should be replaced. If the test light does light, the short to ground is in circuit 120F.

If an intermittent Code 20 is being set, manipulate the related wiring while observing engine data parameter .1.0 with the engine running and the oil pressure switch disconnected. The oil pressure switch should be disconnected since this redundant fuel pump feed can cover-up some circuit malfunctions. If the failure is induced, the "battery voltage" reading will drop from its normal reading to a reading of 0 volts (the engine may also stall). This will help to isolate the location of the malfunction.

Flow Chart, Code 21 - Shorted TPS Circuit. Scheme 74

Flow Chart, Code 21 - Shorted TPS Circuit. Scheme 75

Note. If this code IS NOT displayed during the third pass of diagnostic codes, it is an intermittent failure and cannot be diagnosed using this procedure. For an intermittent code, refer to NOTE ON INTERMITTENTS.

The ECM supplies a 5 volt signal to pin C (circuit 474) of the Throttle Position Sensor (TPS) and supplies a ground path to pin B (circuit 476-X). The TPS signal from pin A (circuit 417) is a variable voltage which is dependent on the throttle position.

Trouble Code 21 indicates that the voltage signal from the TPS is too high. This situation can be observed in engine data display as a "throttle angle" reading (parameter .0.1) of greater than 77 degrees at part throttle. Possible causes of this condition are

1. A. Defective throttle position sensor.
2. B. Defective wiring, terminals, etc.
3. C. An ECM which is unable to process signals properly.

1. If the opposite condition (low TPS signal) can be created, then the self-diagnostics can be used to detect this failure by displaying engine data parameter .0.1. With the opposite condition created, parameter .0.1 should display a throttle angle" reading of 10 to -7 degrees. To create a low sensor signal, disconnect the TPS connector. If the "throttle angle" reading is -10 to -7 degrees circuit 476-X must be checked for an open. If the voltage between circuits 474 and 476-X is 0 volts circuit 476-X is open. If the voltage is 5 volts, the ECM and wiring are OK. The fault must be improper mating of sensor terminals or a faulty TPS sensor.
2. If the "throttle angle" reading is -6 degrees or greater, then there is a short to voltage in the wiring harness or the ECM.

If an intermittent Code 21 is being set, manipulate related wiring while observing engine data parameter .0.1. If the failure is induced, the "throttle angle" reading will jump from its normal value to the "shorted" reading of greater than 77 degrees at part throttle. This will help to isolate the location of the malfunction.

Flow Chart, Code 22 - Open TPS Circuit. Scheme 76

Flow Chart, Code 22 - Open TPS Circuit. Scheme 77

Note. If this code IS NOT displayed during the third pass of diagnostic codes, it is an intermittent failure and cannot be diagnosed using this procedure. For an intermittent code, refer to NOTE ON INTERMITTENTS.

The ECM supplies a 5 volt signal to pin C (circuit 474) of the Throttle Position Sensor (TPS) and supplies a ground path to pin B (circuit 476-X). The TPS signal from pin A (circuit 417) is a variable voltage which is dependent on the throttle position.

Trouble Code 22 indicates that the voltage signal from the TPS is too low. This situation can be observed in engine data display as a "throttle angle" reading (parameter .0.1) of - 10 to -6 degrees at part throttle. Possible causes of this condition are

1. A. A defective throttle position sensor.
2. B. Defective wiring, terminals, etc.
3. C. An ECM which is unable to process signals properly.

1. If the opposite condition (high TPS signal) is created, then the self-diagnostics can be used to detect this failure by displaying engine data parameter .0.1. With the opposite condition created parameter .0.1 should display a throttle angle" reading of 87 to 90 degrees. To create a high TPS signal, disconnect the TPS connector and jumper circuits 417 and 474 together. If the "throttle angle" reading is now 87 to 90 degrees, the fault must be improper mating of sensor terminals or a faulty TPS.
2. If the "throttle angle" reading is 86 degrees or less, measure the voltage on circuit 474. If the voltmeter reads 0 volts, then the throttle position sensor is not receiving 5 volts and circuit 474 must be repaired for an open or short to ground.
3. If the voltmeter reads 5 volts, then measure the voltage between circuits 474 and 417. If the voltage is 5 volts, check circuit 417 for a short to ground. If the wiring is OK, then the fault must be in the ECM connector or ECM itself.
4. If the voltmeter does not read 5 volts, then an open must exist in either the wiring harness or the ECM. If the "throttle angle" reading is stil1 86 degrees or less with circuits 474 and 417 jumpered together at the ECM, the fault must be in the ECM connector or ECM itself. If the reading is 87 to 90 degrees, then circuit 417 is open.

If an intermittent Code 22 is being set, manipulate related wiring while observing the engine data parameter .0.1. If the failure is induced, the "throttle angle" reading will jump from its normal value to the "open" reading of-10 to -6 degrees at part throttle. This will help to isolate the location of the malfunction.

Flow Chart, Code 23 - EST Circuit Problem. Scheme 78

Flow Chart, Code 23 - EST Circuit Problem. Scheme 79

Note. If this code IS NOT displayed during the third pass of diagnostic codes, it is an intermittent failure and cannot be diagnosed using this procedure.

When the engine is cranking, the ECM pulls the HEI bypass line (circuit 462) down to 0 volts and the 0 volt signal commands the HEI module to use base timing. During this "bypass" mode the HEI module grounds the spark timing pulses which are supplied by the ECM on the EST dine (circuit 423). When the engine starts, the ECM pulls the HEI bypass line up to around 5 volts and the 5 volt signal commands the HEI module to use the spark timing pulses which are supplied by the ECM on the EST line.

The ECM monitors the EST line to determine if the HEI module is operating properly. Code 23 indicates that the ECM has failed to see the proper EST signal on circuit 423. Possible causes of this condition are

1. A. A defective HEI module.
2. B. An open set timing connector.
3. C. Defective wires, terminals, etc.
4. D. An ECM not processing the EST signal properly or not pulling the bypass line up to 5 volts.

1. After verifying that the "set timing" connector is properly connected, four jumper wires must be obtained for use in the diagnostic procedure. These jumpers should be about 12 inches long with a male and female weatherpack connector on either end (P/N's 12014836 and 12014837). With the distributor connector disconnected, these jumpers are used to reconnect specific terminals.
2. With the distributor reference circuits reconnected (terminals B and D), the EST signal can be measured on terminal A after the car is started. If this voltage is not between 2.0 and 2.8 volts, an open or short must exist either in circuit 423 or the ECM itself.
3. With circuit 423 between 2.0 and 2.8 volts, the next steps to reconnect terminal A and determine if the HEI module is grounding the EST signal properly in bypass mode. Make sure the ignition is left off for at least 10 seconds to allow the ECM to power-down. If the voltage is greater than 0.5 volts with the engine idling, then circuit 423 is open either in the distributor harness or HEI module itself.
4. With circuit 423 below 0.5 volt, 12 volts should then be applied to the distributor harness terminal C through the resistance of a test light. This will force the HEI module out of the bypass mode. If the voltage on circuit 423 is not between 0.5 and 2.0 volts or if the engine stalls, the fault is in the distributor harness wiring or HEI module itself.
5. If the voltage on circuit 423 is now between 0.5 and 2.0 volts, turn the ignition off for at least 10 seconds to allow the ECM to power-down. With terminal C reconnected and the engine started, circuit 462 should go to greater than 2.0 volts. If the voltage is greater than 2.0 volts the system is working properly at this time. If the voltage remains below 2.0 volts then the fault s either in circuit 462 to the ECM or in the ECM itself.

Flow Chart, Code 24A (W/O Digital Cluster) - Vehicle Speed Sensor (VSS) Circuit Problem. Scheme 80

Flow Chart, Code 24A (W/O Digital Cluster) - Vehicle Speed Sensor (VSS) Circuit Problem. Scheme 81

Note. If this code IS NOT displayed during the third pass of diagnostic codes, it is an intermittent failure and cannot be diagnosed using this procedure. For an intermittent code, refer to NOTE ON INTERMITTENTS.

The speed sensor generates an electrical signal representative of the vehicle speed, and the buffer amplifier amplifies and inverts this signal for the ECM.

Code 24 indicates that a speed signal is not being received by the ECM when the vehicle is in 4th gear. This can be observed in engine data display as a "vehicle speed" reading (parameter .1.2) of 0 MPH while driving. Possible causes of this condition are

1. A. A defective speed sensor.
2. B. A defective buffer amplifier.
3. C. Defective wires, terminals, etc.
4. D. An ECM not able to process the speed signal.
5. E. A speedometer which does not function properly.

1. To begin the diagnosis of trouble Code 24, lift a drive wheel of the car, and measure the voltage on circuit 961 at the ECM. If the voltage varies between .6 and 11 volts when the drive wheel is rotated, then the vehicle must be test driven to determine whether the malfunction was intermittent or if the ECM is not processing this speed signal properly.
2. If there is no voltage variation, the next step is to determine if the voltage signal from the ECM is reaching the buffer amplifier. If the voltage on circuit 961 is 0 volts on the ECM side of the buffer amplifier connector, check the circuit for an open or short to ground. If circuit 961 is OK, check for a faulty ECM connector or faulty ECM.
3. If there is between 10 and 12 volts on circuit 961 then determine if circuit 639 is supplying power to the buffer amplifier. circuit 639 should be at 12 volts when the system is operating properly. If there is no voltage, the 10 amp ignition fuse should be checked and circuit 639 should be repaired as necessary.
4. If 12 volts is present on circuit 639, measure the voltage between it and circuit 151. If the voltage is 0, then circuit 151 is open and not supplying a ground to the buffer amplifier.
5. If there is a reading of 12 volts between circuits 639 and 151, reconnect the buffer amplifier. Backprobe the speed sensor pin G with a voltmeter to ground while manually turning the speedometer drive mechanism. If the voltage varies between 0 and 5 volts, replace the buffer amplifier.
6. If the voltage on speed sensor pin G does not vary, then backprobe speed sensor pin F with the voltmeter to ground. When the circuits are operating properly, pin F will have 4 to 6 volts on it. If the voltage on pin F is 0 volts, replace the buffer amplifier.
7. Backprobe speed sensor pin E with the voltmeter to ground. If the voltage on pin E is within one volt of the voltage on pin F, then replace the buffer amplifier. If the voltage on pin E is more than one volt less than the voltage on pin F, then check for a faulty speed sensor. If the sensor is OK, the problem must be a mechanical malfunction of the speedometer.

If an intermittent Code 24 is being set, lift the drive wheels and let the vehicle idle in low gear. Manipulate the related wiring while observing engine data parameter .1.2. If the failure is induced, the "vehicle speed" reading will drop from its normal value to a reading of 0 MPH. This will help to isolate the location of the malfunction.

Flow Chart, Code 24B (W/ Digital Cluster) - Vehicle Speed Sensor (VSS) Circuit Problem. Scheme 82

Flow Chart, Code 24B (W/ Digital Cluster) - Vehicle Speed Sensor (VSS) Circuit Problem (1 Of 2). Scheme 83

Flow Chart, Code 24B (W/ Digital Cluster) - Vehicle Speed Sensor (VSS) Circuit Problem (2 Of 2). Scheme 84

Note. If this code IS NOT displayed during the third pass of diagnostic codes, it is an intermittent failure and cannot be diagnosed using this procedure. For an intermittent code, refer to NOTE ON INTERMITTENTS.

The speed sensor generates an electrical signal representative of the vehicle speed, and the buffer amplifier amplifies and inverts this signal for the ECM.

Code 24 indicates that a speed signal is not being received by the ECM when the vehicle is in 4th gear. This can be observed in engine data display as a "vehicle speed" reading (parameter .1.2) of 0 MPH while driving. Possible causes of this condition are

1. A. A defective speed sensor.
2. B. A defective buffer amplifier.
3. C. Defective wires, terminals, etc.
4. D. An ECM not able to process the speed signal.
5. E. A speedometer which does not function properly.

1. If the digital cluster displays the vehicle speed properly, then the problem must be in the circuits used only be the ECM. Lift a drive wheel of the car, and measure the voltage on circuit 961 at the ECM. If the voltage varies between .6 and 11 volts when the drive wheel is rotated, then the vehicle must be test driven to determine whether the malfunction was intermittent or if the ECM is not processing this speed signal properly.
2. If there is no voltage variation, the next step is to determine if the voltage signal from the ECM is reaching the buffer amplifier. If the voltage on circuit 961 is 0 volts on the ECM side of the buffer amplifier connector, check the circuit for an open or short to ground If circuit 961 is OK, check for a faulty ECM connector or faulty ECM. If the voltage is between 10 and 17 volts on circuit 961, replace the buffer amplifier.
3. If the digital cluster displays 0 MPH all the time, then the problem must be in those circuits shared between the digital cluster and the ECM. The first step is to verify that the speedometer cable is installed properly. If the cable is properly turning the speedometer, then determine if circuit 39 is supplying power to the buffer amplifier. circuit 39 should be at 12 volts when the system is operating properly. If there is no voltage, the 20 amp GA-TRANS fuse should be checked and circuit 39 should be repaired as necessary.
4. If 12 volts is present on circuit 39, measure the voltage between it and circuit 151. If the voltage is 0, then circuit 151 is open and not supplying a ground to the buffer amplifier.
5. If there is a reading of 12 volts between circuits 39 and 151, reconnect the buffer amplifier. Backprobe the speed sensor pin G with a voltmeter to ground while manually turning the speedometer drive mechanism. If the voltage varies between 0 and 5 volts, replace the buffer amplifier.
6. If the voltage on speed sensor pin G does not vary, then backprobe speed sensor pin F with the voltmeter to ground. When the circuits are operating properly, pin F will have 4 to 6 volts on it. If the voltage on pin F is 0 volts, replace the buffer amplifier.
7. Backprobe speed sensor pin E with the voltmeter to ground. If the voltage on pin E within one volt of the voltage on pin F, then replace the buffer amplifier. If the voltage on pin E is more than one volt less than the voltage on pin F, then check for a faulty speed sensor. If the sensor is OK, the problem must be a mechanical malfunction of the speedometer.

If an intermittent Code 24 is being set, lift the drive wheels and let the vehicle idle in low gear. Manipulate the related wiring while observing engine data parameter .1.2. If the failure is induced, the "vehicle speed" reading will drop from its normal value to a reading of 0 MPH. This will help to isolate the location of the malfunction.

Note On High Idle And/Or Intermittent Code 26

DeVille, Eldorado, Fleetwood and Seville models with DFI may have a high idle and or intermittent Code 26. This condition may be caused by installation of the wrong Throttle Position Sensor (TPS). Whenever replacement of the TPS is necessary, ensure the correct component is installed and adjusted correctly.

CADILLAC TPS APPLICATION TABLE

CADILLAC TPS APPLICATION

Flow Chart, Code 26 - Shorted Throttle Position Switch (TPS) Circuit. Scheme 85

Flow Chart, Code 26 - Shorted Throttle Position Switch (TPS) Circuit. Scheme 86

Note. If this code IS NOT displayed during the third pass of diagnostic codes, it is an intermittent failure and cannot be diagnosed using this procedure. For an intermittent code, refer to NOTE ON INTERMITTENTS.

The ECM supplies a 12 volt signal to pin B, (circuit 427) of the idle speed control motor. When the engine is operating at idle the throttle linkage closes the throttle switch and pulls circuit 427 to 0 volts through the ground circuit of pin A, (circuit 450). When the throttle switch is closed, the ECM and idle speed control motor will precisely control the engine speed for all operating conditions.

Code 26 indicates that ECM is seeing a condition where the throttle switch is closed (indicated by the "Lo" status light being on) with a throttle angle of 13 degrees or more (as displayed on engine data parameter .0.1) Possible causes of this condition are

1. A. A defective throttle switch.
2. B. Defective wire, terminals, etc.
3. C. An ECM which is unable to process signals properly.
4. D. TPS misadjusted or binding.

1. To begin diagnosis, observe the "throttle switch" status light above the "Lo" button while in diagnostics. The light should go off upon application of the throttle. If the light does not go off, refer to the diagnostic decision tree for Code .7.2 since the throttle switch signal is remaining in the "closed" mode. If the status light goes off, then the TPS must be checked for binding or misadjustment.
2. If the sensor is free and correctly adjusted, enter diagnostics and display engine data parameter .0.1. Under the condition of a Code 26 this "throttle angle" reading will be greater than 13 degrees at closed throttle. If the opposite condition (low TPS signal) can be created, then self-diagnostics can be used to detect this failure by displaying engine data parameter .0.1. With the opposite condition created, a "throttle angle" reading of -10 to -7 degrees should be displayed. To create a low sensor signal, disconnect the TPS connector. If the "throttle angle" reading is -10 to -7 degrees circuit 476-X must be checked for an open. If the voltage between circuits 474 and 476-X is 0 volts circuit 476-X is open. If the voltage is volts, the ECM and wiring are OK. The fault must be improper mating of sensor terminals or a faulty TPS sensor.
3. If the "throttle angle reading is -6 degrees or greater, then there is a short to voltage in the wiring harness or the ECM.

If an intermittent Code 26 is being set, operate the vehicle while observing the "throttle switch" status light and "throttle angle" parameter .0.1 simultaneously. If the throttle switch ever fails to open upon application of the throttle, investigate that circuit for a malfunction. If the "throttle angle" ever jumps above 13 degrees with the throttle closed, investigate that circuit for a malfunction. This will help to isolate the location of the malfunction.

Flow Chart, Code 27 - Open Throttle Switch Circuit. Scheme 87

Flow Chart, Code 27 - Open Throttle Switch Circuit. Scheme 88

Note. If this code IS NOT displayed during the third pass of diagnostic codes, it is an intermittent failure and cannot be diagnosed using this procedure. For an intermittent code, refer to NOTE ON INTERMITTENTS.

The ECM supplies a 12 volt signal to pin B, (circuit 427), of the idle speed control motor. When the engine is operating at idle, the throttle linkage closes the throttle switch and pulls circuit 427 to 0 volts through the ground circuit of pin A, circuit 450. When the throttle switch is open, the ISC motor will not try to control idle speed because the driver is controlling the engine speed.

Code 27 indicates that the throttle switch remained open during the previous ignition cycle and has not yet closed during the present ignition cycle. Possible causes are

1. A. A defective throttle switch.
2. B. Defective wires, terminals, etc.
3. C. An ECM which is unable to process signals properly.

1. To begin diagnosis, observe the "throttle switch" status light above the "Lo" button while in diagnostics. If the system is operating properly, the light should come on as the throttle is released. If the light does not come on, refer to the diagnostic decision tree for Code .7.2 since the throttle switch signal is remaining in the "open" mode.
2. If the status light comes on, exit diagnostics while in this "closed" throttle mode. Under this condition, the check engine light should go out and Code 27 should remain as an intermittent failure. If the Code 27 remains a hard failure, replace the ECM since it is not processing the signal properly.

If an intermittent Code 27 is being set. Observe the "throttle switch" status light while operating the vehicle. If the throttle switch ever fails to "close" upon release of the throttle, investigate the circuit for a malfunction. Other things to check are misadjusted "minimum air rate", binding throttle linkage or binding ISC plunger.

Flow Chart, Code 28 - Open 4th Gear Circuit. Scheme 89

Flow Chart, Code 28 - Open 4th Gear Circuit. Scheme 90

Note. If this code IS NOT displayed during the third pass of diagnostic codes, it is an intermittent failure and cannot be diagnosed using this procedure. For an intermittent code, refer to NOTE ON INTERMITTENTS.

The ECM supplies a 12 volt signal on circuit 438 to the transmission fourth gear switch. The fourth gear switch pulls this circuit to ground when the transmission is in any mode except fourth gear. The ECM senses fourth gear operation when the switch opens due to fourth gear oil pressure.

Code 28 indicates that the ECM is seeing 12 volts on circuit 438 when the transmission is in reverse. Possible causes of this condition are

1. A. A defective fourth gear switch.
2. B. Defective wire, terminals, etc.
3. C. An ECM not able to process signals properly.

1. To begin diagnosis, determine if the ECM can recognize the grounding of circuit 438 at the transmission connector. If the "fourth gear" status light is on, then there is an open in either circuit 438 or the ECM. If the light remains on with circuit 438 grounded at the ECM then either the ECM connector or ECM is faulty. If the light goes off, then circuit 438 is open.
2. If the status light is off, then the ECM is functioning properly and the fault must be in the transmission. If the test light on pin B at the transmission does not light, then an open must exist in the wiring or fourth gear switch. If the test light fails to light on the fourth gear switch terminal, then it is open and should be replaced. If the test light does light, the open is between the transmission connector and fourth gear switch connector.
3. If the test light on pin B lights, then the fourth gear switch is working properly. If the test light goes out when the engine is started and put into reverse then the switch is receiving oil pressure when it should not be. Refer to transmission diagnosis.
4. If the test light stays on, then the transmission connector should be reconnected and the "fourth gear" status light should be checked for proper operation. If the light is on, then the fault must be improper mating of circuit 438 terminals at pin B of the transmission connector. If the light is off, then the malfunction is not present at this time.

If an intermittent Code 28 is being set, manipulate the related wiring while observing the "fourth gear" status light above the "hi" button on the ECC control head. If the failure is induced, the status light will turn on. This will help in isolating the location of the malfunction.

Flow Chart, Code 29 - Shorted 4th Gear Circuit. Scheme 91

Flow Chart, Code 29 - Shorted 4th Gear Circuit. Scheme 92

Note. If this code IS NOT displayed during the third pass of diagnostic codes, it is an intermittent failure and cannot be diagnosed using this procedure. For an intermittent code, refer to NOTE ON INTERMITTENTS.

The ECM supplies a 12 volt signal on circuit 438 to the transmission fourth gear switch. The fourth gear switch pulls this circuit to ground when the transmission is in any mode except fourth gear. The ECM senses fourth gear operation when the switch opens due to fourth gear oil pressure.

Code 29 indicates that the ECM is seeing circuit 438 grounded when the transmission should be in fourth gear (above 50 MPH with the throttle switch closed). Possible causes of this condition are

1. A. A defective fourth gear switch
2. B. Defective wire, terminals, etc.
3. C. An ECM not able to process signals properly.

1. To begin diagnosis, determine if the ECM can recognize an open in circuit 438 at the transmission connector. If the "fourth gear" status light is off, then either circuit 438 or the ECM is shorted to ground.
2. If the status light is on, then the ECM is functioning properly and the fault must be in the transmission. If a road test indicates that the vehicle is unable to shift into fourth gear, refer to appropriate TRANSMISSION SERVICING article for transmission diagnosis.
3. If the vehicle is shifting into fourth gear, then the "fourth gear" status light should be checked for proper operation. If the light is on while in fourth gear then the malfunction is not present at this time.
4. If the status light is not on while in fourth gear, then the fault must be in the transmission. If the status light is on with the fourth gear switch disconnected, the switch must be failing to open and should be replaced. If the light is off there is a short to ground between the transmission connector and the fourth gear switch connector.

If an intermittent Code 29 is being set, the wiring outside the transmission can be checked using diagnostic display. Disconnect the transmission connector and observe the "fourth gear" status light above the "hi" button on the ECC control head. The light will be on with the circuit open. Manipulate the related wring while observing the status light. If the failure is induced, the light will turn off. This wil1 help to isolate the location of the malfunction.

A Code 29 can also be set if the drive (ADL) switch is misadjusted. If the switch remains closed when the vehicle is shifted into neutral it would look to the ECM as if the vehicle is still in drive. This condition would result in an intermittent Code 29 if the vehicle were shifted into neutral while driving above 50 MPH.

Flow Chart, Code 30 - ISC Circuit Problem. Scheme 93

Flow Chart, Code 30 - ISC Circuit Problem (1 Of 2). Scheme 94

Flow Chart, Code 30 - ISC Circuit Problem (2 Of 2). Scheme 95

Note. The following procedure is designed to account for intermittent codes. If no malfunction is uncovered using this procedure, it will indicate that the DFI system is OK at this time. Refer to NOTE ON INTERMITTENTS if further investigation is necessary.

When trouble Code 30 is set, the check engine light remains on for the entire ignition cycle and ISC operation is not tested again until the next ignition cycle. This means that an intermittent malfunction will appear as a hard failure during the ignition cycle in which it occurs. The ECM, even though it has recognized a malfunction in the ISC operation, will continue trying to control idle speed.

The ISC motor tries to control idle speed to a specified RPM whenever the throttle switch, located inside the ISC housing, is closed. The ECM determines whether the ISC motor is functioning properly by monitoring the resultant change in TPS readings as ISC motor operation is commanded.

Trouble Code 30 indicates that either of the following two conditions have occurred

I. After commanding the ISC motor to retract for 15 seconds, the actual RPM remained more than 150 over that specified and the throttle angle remained greater than 2.5 degrees.

II. After commanding the ISC motor to extend for 15 seconds, the actual RPM remained more than 150 below that specified and the throttle angle remained less than 9 degrees. Possible causes of these conditions are

1. A. A misadjusted TPS.
2. B. A misadjusted ISC motor.
3. C. A defective ISC motor.
4. D. A defective throttle switch.
5. E. A defect in wiring, terminals, etc.
6. F. An ECM which is unable to process the signal properly.

1. To begin diagnosis, determine if the throttle switch is working properly by performing the "switch tests". If Code .7.2 does not pass, refer to the Code .7.2 Diagnostic Decision Tree.
2. If Code .7.2 passes, then the next step is to verify that the ISC motor retracts and extends when commanded to do so by the ECM. To exercise the ISC motor, proceed as follows: A. Enter diagnostics and display "output cycling" Code .9. 6. B. Cycle the throttle switch to begin "output cycling". C. Visually check to see if the ISC motor extends and retracts.
3. If the ISC motor extends and retracts, then check for a binding TPS sensor. Also check the minimum air rate, TPS and ISC adjustments as described in Section 6 of the Service Manual. At this point, the checks and adjustments of the circuits which might set Code 30 have been completed, and Code 30 should not reappear. If no problems are found and Code 30 continues to be set, check for a faulty ECM connector or faulty ECM.
4. If the ISC motor fails to extend or retract, check the throttle linkage for free movement. If the throttle is not binding, disconnect the ISC connector and jumper pins A and B together. While in "output cycling," connect a test light between harness connector pin D and ground. If the test light flashes for 3 seconds and is off for 3 seconds, then circuit 425 is OK. Connect the test light between harness connector pin C and ground with pins A and B still jumpered together. If the test light flashes for 3 seconds and is off for 3 seconds, then circuit 426 is OK. If a test light across pin C and pin D flashes continuously, the problem must be in the ISC terminals or ISC motor. If the test light fails to light or flashes for 3 seconds and is off for 3 seconds then the problem is the ECM failing to provide a ground for the ISC motor. Check for a faulty ISC connector or faulty ISC motor.
5. If either circuit 425 or 426 fail to flash the test light, they should be checked for opens, shorts to ground or a short between the two circuits. If a short is discovered, the ECM may have been damaged and may not be able to control the ISC motor. If no opens or shorts are found, the fault must be in the ECM connector or or ECM itself.

If an intermittent Code 30 is being set before cold starts, the ISC motor may not be adjusted properly. To simulate a cold start, turn the ignition on, enter diagnostics and then momentarily disconnect the coolant temp sensor connector. Being in diagnostics will keep Code 15 from setting and the ECM will see a coolant temperature reading of -40° to -35°C. If the ISC motor ratchets at this point, the minimum air rate, TPS and ISC motor adjustments should be checked.

If an intermittent Code 30 is being set after start-up, manipulate related wiring while in output cycling (code .9.6). If the failure is induced, the ISC motor will stop cycling in one or both directions. This will help to isolate the location of the malfunction.

A Code 30 may be stored along with a Code 19 Shorted Fuel Pump Circuit. If Code 30 no longer appears after Code 19 has been corrected, do not investigate any further. The voltage on the fuel pump feedback circuit made the ECM improperly test Code 30.

Flow Chart, Code 31 - Shorted Map Sensor Circuit. Scheme 96

Flow Chart, Code 31 - Shorted Map Sensor Circuit. Scheme 97

Note. If this code IS NOT displayed during the third pass of diagnostic codes, it is an intermittent failure and cannot be diagnosed using this procedure. For an intermittent code, refer to NOTE ON INTERMITTENTS.

The ECM supplies a 5 volt signal to pin C (circuit 474) of the Manifold Absolute Pressure (MAP) Sensor and supplies a ground path to pin A (circuit 476-Y). The MAP signal from pin B (circuit 432) is a variable voltage which is dependent on the manifold pressure.

Trouble Code 31 indicates that the voltage signal from the MAP sensor is too high. This situation can be observed in engine data display as a "MAP" reading (parameter .0.2) of 106 to 108 kPa. Possible causes of this condition are

1. A. Defective MAP sensor.
2. B. Defective wiring, terminals, etc.
3. C. An ECM which is unable to process signals properly.

1. If the opposite condition (low MAP signal) can be created, then the self-diagnostics can be used to detect this failure by displaying engine data parameter .0.2. With the opposite condition created, parameter .0.2 should display a "MAP" reading of 14 to 16 kPa. To create a low sensor signal, disconnect the MAP sensor connector. If the "MAP" reading is 14 to 16 kPa, then the problem must be a faulty MAP sensor. If the "MAP" reading is 17 kPa or greater, then there is a short to voltage in the wiring or the ECM.

Do not investigate an intermittent Code 31 if the vehicle has a history of engine backfires. A backfire can produce a manifold pressure greater than 106 kPa and set this code. If an intermittent Code 31 is being set, manipulate related wiring while observing engine data parameter .0.2. If the failure is induced, the MAP reading will jump from its normal value to the "shorted" reading of 106 to 108 kPa. This will help to isolate the location of the malfunction.

Flow Chart, Code 32 - Open Map Sensor Circuit. Scheme 98

Flow Chart, Code 32 - Open Map Sensor Circuit. Scheme 99

Note. If this code IS NOT displayed during the third pass of diagnostic codes, it is an intermittent failure and cannot be diagnosed using this procedure. For an intermittent code, refer to NOTE ON INTERMITTENTS.

The ECM supplies a 5 volt signal to pin C (circuit 474) of the Manifold Absolute Pressure (MAP) sensor and supplies a ground path to pin A (circuit 476-Y). The MAP signal from pin B (circuit 432) is a variable voltage which is dependent on the manifold pressure.

Trouble Code 32 indicates that the voltage signal from the MAP sensor is too low. This situation can be observed in engine data display as a "MAP" reading (parameter .0.2) of 14 to 16 kPa. Possible causes of this condition are

1. A. A defective MAP sensor.
2. B. Defective wiring, terminals, etc.
3. C. An ECM which is unable to properly process signals.

1. If the opposite condition (high MAP signal) is created, then the self-diagnostics can be used to detect this failure by displaying engine data parameter .0.2. With the opposite condition created parameter .0.2 should display a MAP reading of 106 to 108 kPa. To create a high "MAP" signal, disconnect the MAP sensor connector and jumper circuits 432 and 474 together. If the "MAP" reading is now 106 to 108 kPa, the fault must be improper mating of sensor terminals or a faulty MAP sensor.
2. If the "MAP" reading is 105 kPa or less, measure the voltage on circuit 474. If the voltmeter reads 0 volts, then the MAP sensor is not receiving 5 volts and circuit 474 must be repaired for an open or short to ground.
3. If the voltmeter reads 5 volts, then measure the voltage between circuits 474 and 432. If the voltage is 5 volts, check circuit 432 for a short to ground. If the wiring is OK, then the fault must be in the ECM connector or ECM itself.
4. If the voltmeter does not read 5 volts, then an open must exist in either the wiring harness or the ECM. If the "MAP" reading is still 105 kPa or less with circuits 474 and 432 jumpered together at the ECM the fault must be in the ECM connector or ECM itself. If the reading is 106 to 108 kPa, then circuit 432 is open.

If an intermittent Code 32 is being set, manipulate related wiring while observing the engine data parameter .0.2. If the failure is induced, the "MAP" reading will jump from its normal value to the "open" reading of 14 to 16 kPa. This will help to isolate the location of the malfunction.

Flow Chart, Code 33 - MAP/BARO sensor correlation. Scheme 100

Flow Chart, Code 33 - MAP/BARO sensor correlation. Scheme 101

Note. The following procedure is designed to account for intermittent codes. If no malfunction is uncovered using this procedure, it will indicate that the DFI system is OK at this time. Refer to NOTE ON INTERMITTENTS if further investigation is necessary.

Code 33 indicates that the ECM has seen a condition where the Manifold Absolute Pressure (MAP) sensor signal and the Barometric Pressure (BARO) sensor signal should have been the same voltage but were not (ignition on but the engine not running or cranking). Possible causes of this condition are

1. A. A faulty MAP sensor.
2. B. A faulty BARO sensor.
3. C. Defective wires, terminals, etc.
4. D. An ECM not processing the signals properly.

1. Begin diagnosis by determining whether the code is hard, intermittent or a sensor response problem. If after 10 seconds at ignition on, the code does not set either as a hard code or an intermittent, then the malfunction s not present at this time.
2. If Code 33 is stored as a hard code after 10 seconds at ignition on, then this condition can be verified by displaying engine data parameters .0.2 and .0.3. The two pressure readings will differ by 2 or more kPa at ignition on. This could be caused by an open in one of the sensor ground circuits. If one of the sensor readings moves closer to the other when the ground circuits (476-X and 476-Y) are jumpered together, then the circuit to the sensor which changed in value is open.
3. If neither reading moved, one of the sensors is faulty. To determine which sensor to replace, obtain a replacement MAP or BARO sensor and connect it to the appropriate harness connector. Compare this sensor's parameter value to those recorded previously. If the new sensor reads closer to the original reading for the BARO sensor, replace the MAP sensor. If the new sensor reads closer to the MAP sensor, replace the BARO sensor.
4. If Code 33 was stored as an intermittent after 10 seconds at ignition on, one of the sensor's may be responding too slowly when power is applied. To determine if this is the case, observe each sensor's parametric value as the sensor is reconnected. A good sensor should go to its maximum value without displaying more than one intermediate value. If several values are displayed before the maximum, replace the affected sensor. If both respond properly, the ECM may not be processing the signals properly.

If an intermittent Code 33 is being set, manipulate related wiring while observing engine data parameters .0.2 and .0.3. If the failure is induced, one of the pressure sensor readings will change to produce a larger "correlation" difference. This will help to isolate the location of the malfunction.

Code 33 is more difficult to induce if the "outside temperature" reading is not between 50°F and 130°F. The ECM allows for a greater difference between the pressure sensors if the ambient temperature is extreme.

Flow Chart, Code 34 - MAP Signal Too High. Scheme 102

Flow Chart, Code 34 - MAP Signal Too High. Scheme 103

Note. If this code IS NOT displayed during the third pass of diagnostic codes, it is an intermittent failure and cannot be diagnosed using this procedure. For an intermittent code, refer to NOTE ON INTERMITTENTS.

Trouble Code 34 indicates that the Manifold Absolute Pressure sensor (MAP) signal and the Barometric Pressure sensor (BARO) signal have closed to the same value when the engine is running. This condition can be observed in engine data display as MAP (parameter .0.2) and BARO (parameter .0.3) readings within 6 kPa of each other with the engine running at idle. When the ignition is on and the engine is not cranking or running, both sensors should read the same voltage value because they are reading atmospheric (barometric) pressure. As the engine starts to turn over, the MAP sensor should read manifold pressure. Possible causes of Code 34 are

1. A. A MAP hose leak or blockage.
2. B. Defective wires, terminals, etc.
3. C. An ECM not processing the signals properly.

1. After verifying the failure condition, the MAP hose should be inspected for leaks or blockages and repaired as necessary.
2. If the MAP hose is OK, create a low sensor signal by disconnecting the MAP sensor. If the "MAP" reading is 17 kPa or greater, then either the wiring harness or the ECM is shorted to voltage. If no defect is found in circuit 432 then the short to voltage is either in the ECM connector or in the ECM itself
3. If the "MAP" reading is 14 to 16 kPa, circuit 476-Y must be checked for an open. If the voltage between circuits 474 and 476-Y is 0 volts, circuit 476-Y is open. If the voltage is 5 volts, the ECM and wiring are OK. The fault must be improper mating of sensor terminals or a faulty MAP sensor.

If an intermittent Code 34 is being set, manipulate related wiring while observing engine data parameter .0.2 with the engine running. If the failure is induced, the "MAP" reading will jump from its normal value at idle to within 6 kPa of the BARO reading (parameter .0.3). This wil1 help to isolate the location of the malfunction.

Flow Chart, Code 35 - Shorted BARO Sensor Circuit. Scheme 104

Flow Chart, Code 35 - Shorted BARO Sensor Circuit. Scheme 105

Note. If this code IS NOT displayed during the third pass of diagnostic codes, it is an intermittent failure and cannot be diagnosed using this procedure . For an intermittent code, refer to NOTE ON INTERMITTENTS.

The ECM supplies a 5 volt signal to pin C (circuit 474) of the Barometric pressure (BARO) sensor and supplies a ground path to pin A (circuit 476-X). The BARO signal from pin B (circuit 433) is a variable voltage which is dependent on the barometric pressure.

Trouble Code 35 indicates that the voltage signal from the BARO sensor is too high. This situation can be observed in engine data display as a "BARO" reading (parameter .0.3) of 106 to 108 kPa. Possible causes of this condition are

1. A. Defective BARO sensor.
2. B. Defective wiring, terminals, etc.
3. C. An ECM which is unable to properly process signals.

1. If the opposite condition (low BARO signal) can be created, then the self-diagnostics can be used to detect this failure by displaying engine data parameter .0.3. With the opposite condition created, parameter .0.3 should display a "BARO" reading of 14 to 16 kPa. To create a low sensor signal, disconnect the BARO sensor connector. If the "BARO" reading is 14 to 16 kPa, then the problem must be a faulty BARO sensor. If the "BARO" reading is 17 kPa degrees or greater, then there is a short to voltage in the wiring or the ECM.

If an intermittent Code 35 is being set, manipulate related wiring while observing engine data parameter .0.3. If the failure is induced, the "BARO" reading will jump from its normal value to the "shorted" reading of 106 to 108 kPa. This will help to isolate the location of the malfunction.

Flow Chart, Code 36 - Open BARO Sensor Circuit. Scheme 106

Flow Chart, Code 36 - Open BARO Sensor Circuit. Scheme 107

Note. If this code IS NOT displayed during the third pass of diagnostic codes, it is an intermittet1t failure and cannot be diagnosed using this procedure. For an intermittent code, refer to NOTE ON INTERMITTENTS.

The ECM supplies a 5 volt signal to pin C (circuit 474) of the Barometric Pressure (BARO) sensor and supplies a ground path to pin A (circuit 476-X). The BARO signal from pin B (circuit 433) is a variable voltage which is dependent on the barometric pressure.

Trouble Code 36 indicates that the voltage signal from the BARO sensor is too low. This situation can be observed in engine data display as a "BARO" reading (parameter .0.3) of 14 to 52 kPa. Possible causes of this condition are

1. A. A defective BARO sensor.
2. B. Defective wiring, terminals, etc.
3. C. An ECM which is unable to process signals properly.

1. If the opposite condition (high BARO signal) is created, then the self-diagnostics can be used to detect this failure by displaying engine data parameter .0.3. With the opposite condition created parameter .0.3 should display a "BARO" reading of 106 to 108 kPa. To create a high BARO signal, disconnect the BARO sensor com1ector and jumper circuits 433 and 474 together. If the "BARO" reading is now 106 to 108 kPa the fault must be improper mating of sensor terminals or a faulty BARO sensor.
2. If the "BARO" reading is 105 kPa or less, measure the voltage on circuit 474. If the voltmeter reads 0 volts, then the BARO sensor is not receiving 5 volts and circuit 474 must be repaired for an open or short to ground.
3. If the voltmeter reads 5 volts, then measure the voltage between circuits 474 and 433. If the voltage is 5 volts, check circuit 433 for a short to ground. If the wiring is OK, then the fault must be in the ECM connector or ECM itself.
4. If the voltmeter does not read 5 volts, then an open must exist in either the wiring harness or the ECM. If the BARO reading is still 105 kPa or less with circuits 474 and 433 jumpered together at the ECM, the fault must be in the ECM connector or ECM itself. If the reading is 106 to 108 kPa, then circuit 433 is open.

If an intermittent Code 36 is being set, manipulate related wiring while observing the engine data parameter .0.3. If the failure is induced, the "BARO" reading will jump from its normal value to the "open" reading of 14 to 52 kPa. This wil1 help to isolate the location of the malfunction.

Flow Chart, Code 37 - Shorted MAT Sensor Circuit. Scheme 108

Note. If this code IS NOT displayed during the third pass of diagnostic codes, it is an intermittent failure and cannot be diagnosed using this procedure. For an intermittent code, refer to NOTE ON INTERMITTENTS.

Trouble Code 37 indicates that the MAT sensor signal voltage is too low. This condition will be observed in engine data display as a "MAT" reading (parameter .0.5) of 142° to 151°C. Possible causes of this condition are

1. A. A shorted MAT sensor.
2. B. Defective wiring, terminals, etc.
3. C. ECM not processing the MAT signal properly.

1. If the opposite failure mode (open sensor) is created, then the self-diagnostics can be used to detect this failure by displaying engine data parameter .0.5. With the opposite failure created, parameter .0.5 should display a "MAT" reading of -40° to -35°C. To create an open sensor signal, disconnect the MAT sensor connector. If the "MAT" reading is now -40° to -35°C the ECM and the wiring harness are OK. The fault must be in the MAT sensor itself.
2. If the "MAT" reading is -34°C or greater, then there is a short to ground in the wiring harness or the ECM.

If an intermittent Code 37 is being set, manipulate the related wiring while observing engine data parameter .0.5. If the failure is induced, the "MAT" reading will jump from its normal value to the "shorted" reading of 142° to 151°C. This will help to isolate the location of the malfunction.

Flow Chart, Code 38 - Open MAT Sensor Circuit. Scheme 109

Flow Chart, Code 38 - Open MAT Sensor Circuit. Scheme 110

Note. If this code IS NOT displayed during the third pass of diagnostic codes, it is an intermittent failure and cannot be diagnosed using this procedure. For an intermittent code, refer to NOTE ON INTERMITTENTS.

Trouble Code 38 indicates that the MAT sensor signal voltage is too high. This condition will be observed in engine data display as a "MAT" reading (parameter .0.5) of-40° to -35°C. Possible causes of this condition are

1. A. An open MAT sensor.
2. B. Defective wiring, terminals. etc.
3. C. An ECM not processing the MAT signal properly.

1. If the opposite failure mode (shorted sensor) is created, then the self-diagnostics can be used to detect this failure by displaying engine data parameter .0.5. With the opposite failure created, parameter .0.5 should display a "MAT" reading of 148° to 151°C. To create a shorted sensor signal, disconnect the MAT sensor and jumper the harness terminals together. If the "MAT" reading is 148° to 151°C, the ECM and the wiring harness are OK. The fault must be in the sensor connector or MAT sensor itself
2. If the "MAT" reading is 147°C or less, then there is an open in the signal circuit 472, in the sensor ground circuit 476-Y, or in the ECM. If the "MAT" reading is now 148° to 151°C with circuit 472 jumpered to ground, an open exists in circuit 476-Y.
3. If the "MAT" reading remains 147°C or less with circuit 472 jumpered to ground at the ECM, either the ECM connector or ECM itself is faulty. If the reading is now 148° to 151°C an open exists in circuit 472.

If an intermittent Code 38 is being set, manipulate related wiring while observing engine data parameter .0.5. If the failure is induced, the "MAT" reading will drop from its normal value to the "open" reading of -40° to -35°C. This will help to isolate the location of the malfunction.

Flow Chart, Code 39 - TCC Engagement Problem. Scheme 111

Flow Chart, Code 39 - TCC Engagement Problem (1 Of 2). Scheme 112

Flow Chart, Code 39 - TCC Engagement Problem (2 Of 2). Scheme 113

Note. The following procedure is designed to account for intermittent codes. If no malfunction is uncovered using this procedure, it will indicate that the DFI system is OK at this time. Refer to NOTE ON INTERMITTENTS if further investigation is necessary.

The ECM completes the circuit for the TCC solenoid by grounding circuit 422. Grounding this circuit allows the solenoid to energize and supply oil pressure to the torque converter clutch.

Code 39 indicates that the ECM is seeing the engine speed at a greater RPM than would be expected at 55 MPH with the TCC engaged. Possible causes of this condition are

1. A. A defective TCC solenoid
2. B. A defective TCC brake switch
3. C. Defective wiring, terminals, etc.
4. D. An ECM not able to process signals properly

1. To begin diagnosis connect a test light to circuit 422 on the ALDL diagnostic connector (pin F). With the TCC disengaged (ECM not grounding circuit 422) the test light should see 12 volts and light.
2. If the test light lights, then power is being supplied through the TCC brake switch. While in output cycling, circuit 422 should go between 12 volts and 0 volts every 3 seconds. If the test light does not flash the transmission should be checked for a shorted circuit. If the resistance between pins A and D is less than 15 ohms. The solenoid or the wires are shorted and should be repaired. This low resistance through the transmission may have damaged the ECM, therefore, after repairs have been made, check the output of the ECM in output cycling. If the resistance is greater than 15 ohms, then circuit 422 should be checked for an open to the ECM. If the wire is OK, check for a faulty ECM connector or faulty ECM.
3. If the test-light goes on and off every 3 seconds, then the ECM and wiring is OK. The fault could be a mechanical problem in the transmission, therefore a road test should be performed. At 55 MPH with the TCC solenoid energized (test-light off), the engine RPM is a factor of the driveline gear ratio if the TCC is working properly. At 55 MPH, engine data parameter .1.1 (engine speed) should read: ENGINE DATA PARAMETER Vehicle Low & All Altitude High Altitude Only Eldorado/Seville 1600 RPM 1700 RPM DeVille/Brougham 1700 RPM 1850 RPM If the RPM reading is greater than this limit, the TCC has failed to engage and should be diagnosed by referring to appropriate section.
4. If the test light does not light on circuit 422, then there must be an open between the ALDL connector and the battery. First check the TCC brake switch for proper operation. If there is not voltage on both sides of the connector either the switch or the circuit feeding the switch is open.
5. If there is voltage on both sides of the TCC brake switch, then the voltage on circuit 420 should be checked at the transmission. If the test light does not light, circuit 420 is open If the test/light between circuits 420 and 422 does not light with Pin F jumpered to ground, then circuit 422 is open. If the test/light does light then the open must exist either at the transmission connector terminals or within the transmission itself.

If an intermittent Code 39 is being set, it could be due to the adjustment of the brake switches. The ECM does not test for the TCC code if it sees the brake applied through the cruise control brake signal on circuit 919. This is because the TCC brake switch is also open under this condition. If the TCC brake switch is adjusted such that it opens before the Cruise Control brake switch. A Code 39 could be set if the operator were to keep the brake pedal applied just enough to open the TCC switch but not the Cruise Control switch.

Flow Chart, Code 44 - Lean Exhaust Signal. Scheme 114

Flow Chart, Code 44 - Lean Exhaust Signal. Scheme 115

Note. The following procedure is designed to account for intermittent codes. If no malfunction is uncovered using this procedure, it will indicate that the DFI system is OK at this time. Refer to NOTE ON INTERMITTENTS if further investigation is necessary.

When the 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 oxygen sensor is warm (above 200°C), the output voltage will swing between 0 and 1.0 volt. When the ECM sees that the oxygen sensor is not at the cold voltage of 0.5 volt, it will send the system into closed loop operation. In closed loop operation, the ECM will meter the fuel into the engine based on the oxygen sensor readings.

Code 44 indicates that the oxygen sensor voltage reading is below .5 volts and wil1 not swing above. If the voltage remains in this low range, the ECM will set Code 44 and return the system to open loop operation. Possible causes of this condition are

1. A. The oxygen sensor not functioning properly.
2. B. Defective wires, terminals, etc.
3. C. Improper fuel delivery.
4. D. The ECM not processh1g the signal properly.

1. To check the operation of the oxygen sensor circuit, turn the ignition on and display engine data parameter .0.7. If the "oxygen sensor voltage" reads less than .37 volts with the sensor disconnected, check circuit 412 for a short to ground or a short to circuit 413. If circuit 412 is OK, check for a faulty ECM connector of faulty ECM.
2. If the voltage is greater than .37 volts, then jumper the oxygen sensor harness pins together (ECM side) and note the voltage reading. If the voltage reading is greater than .05 volts, then the ECM is not able to recognize that a fault was artificially created. Check circuits X412 and 413 for an open. If no defect is found, check for a faulty ECM connector or faulty ECM.
3. If the voltage reading is less than .05 volts, then the ECM is functioning properly and the harness is OK. Reconnect the oxygen sensor and clear Code 44 before existing diagnostics. (Code 44 must be cleared prior to checking air management. This is because air management is disabled whenever a hard Code 44 is present). The diagnosis should now center on determining why the fuel mixture is lean. A fuel delivery system which is not functioning properly will cause a lean fuel mixture. This malfunction can be caused by fuel pressure less than 9 PSI at the injectors, by defective injectors, etc. Refer to the performance diagnosis «CHART 4 - FUEL SYSTEM»(/cadillac/fleetwood/75-series-1956-1992/remont/testing-diagnostics/#dfi-tests-wcodes) , for additional information. A loss of EGR wil1 causes a lean fuel mixture. Refer to the performance diagnosis CHART 7 - EGR DIAGNOSIS, for additional information. If the AIR management system were to send to the exhaust ports at all times, this oxygen would give a lean indication at the oxygen sensor. Refer to the performance diagnosis «CHART 8»(/cadillac/fleetwood/75-series-1956-1992/remont/testing-diagnostics/#dfi-tests-wcodes) for additional information. If the OXYGEN SENSOR TEST indicates that the sensor is OK, then check all connectors, terminals, etc. for an intermittent code.

If an intermittent Code 44 is being set, manipulate related wiring while observing engine data parameter .0.7 at part throttle with the engine warm. If the failure is induced, the "oxygen sensor" reading will change from its normal fluctuating voltage (above .60 and below .30) to a reading never going above .50 volts. This will help to isolate the location of the malfunction.

Flow Chart, Code 45 - Rich Exhaust Signal. Scheme 116

Flow Chart, Code 45 - Rich Exhaust Signal. Scheme 117

Note. The following procedure is designed to account for intermittent codes. If no malfunction is uncovered using this procedure, it will indicate that the DFI system is OK at this time. Refer to NOTE INTERMITTENTS if further investigation is necessary.

When the 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 oxygen sensor is warm (above 200°C), the output voltage will swing between 0 and 1.0 volt. When the ECM sees that the oxygen sensor is not at the cold voltage of 0.5 volt, it will send the system into closed loop operation. In closed loop operation the ECM will meter the fuel into the engine based on the oxygen sensor readings.

Code 45 indicates that the oxygen sensor voltage reading is above .5 volts and will not swing below. If the voltage remains in this high range, the ECM will set Code 45 and return the system to open loop operation. Possible causes of this condition are

1. A. The oxygen sensor not functioning properly.
2. B. Defective wires, terminals, etc.
3. C. Improper fuel delivers:.
4. D. The ECM not processing the signal properly.

1. To check the operation of the oxygen sensor circuit turn the ignition on and display engine data parameter .0.7. If the oxygen sensor voltage reads greater than .57 volts with the sensor disconnected check circuit 412 for a short to voltage. If circuit 412 is OK, check for a faulty ECM connector or faulty ECM.
2. If the voltage is less than .57 volts, then jumper the oxygen sensor harness pins together (ECM side) and note the voltage reading. If the voltage reading is greater than .05 volts, then the ECM is not able to recognize that a fault was artificially created. Check circuits 412 and 413 for an open. If no defect is found, check for a faulty ECM connector or faulty ECM.
3. If the voltage reading is less than .05 volt, then the ECM is functioning properly and the harness is OK. Reconnect the oxygen sensor. The diagnosis should now center on determining why the fuel mixture is rich. A fuel delivery system which is not functioning properly will cause a rich fuel mixture. This malfunction can be caused by fuel pressure which is greater than 12 PSI at the injectors, by defective injectors, etc. Refer to the performance diagnosis «CHART 4 - FUEL SYSTEM»(/cadillac/fleetwood/75-series-1956-1992/remont/testing-diagnostics/#dfi-tests-wcodes) , for additional information. A restricted air cleaner could cause a rich fuel mixture. Inspect the cleaner and replace if necessary. If the OXYGEN SENSOR TEST, ( «CHART 14»(/cadillac/fleetwood/75-series-1956-1992/remont/testing-diagnostics/#dfi-tests-wcodes) ) indicates that the sensor is OK, then check all connectors, terminals, etc. for an intermittent code.

If an intermittent Code 45 is being set, manipulate related wiring while observing engine data parameter .0.7 at part throttle with the engine warm. If the failure is induced, the oxygen sensor reading will change from its normal fluctuating voltage (above .60 and below .30) to reading never going below .50 volts. This wild help to isolate the location of the malfunction.

CODE 51 - PROM ERROR INDICATOR

If code 51 is a hard failure, it will be displayed continuously until diagnostic mode is exited. If code 51 is an intermittent failure, it will be displayed only in the first 2 passes of diagnostic display. Code 51 indicates that the calibration PROMS are not being read properly by the ECM.

PROMS installed backwards or PROMS installed with missing or bent pins may cause this code to set. Remove PROM cover on ECM and verify that PROMS are installed correctly.

If the PROMS appear to be installed correctly, turn the ignition off for 10 seconds and then check if code 51 remains. If so, replace PROMS. Turn ignition off for 10 seconds and check for code 51. If code remains after replacing PROMS, replace ECM.

If Code 51 is a hard failure, it will be displayed continuously until the diagnostic mode is exited. If Code 51 is an intermittent it will be displayed in the first 2 passes of diagnostic display. Code 51 indicates that the calibration PROMS are not being read properly by the ECM.

PROMS installed backwards or PROMS installed with their pins bent or missing may cause this Code to set. Remove the trap door on the ECM and verify that the calibration PROMS are installed properly. Refer to the "On Car Service" section of the Service Manual to obtain additional information on how to install calibration PROMS.

If the PROMS appear to be installed properly, turn the ignition off for 10 seconds and then check if Code 51 remains. If it does remain, replace the PROMS. Again turn the ignition off for 10 seconds and check for Code 51. If the code remains after replacing the PROMS. replace the ECM.

CODE 52 - ECM MEMORY RESET INDICATOR

Code 52 indicates that "long term" memory in ECM has been reset. This will happen whenever power is removed from ECM. This code should be cleared from memory after restoring power to ECM.

Code 52 indicates that the long term memory in the ECM has been reset. This will be the case whenever power is removed from the ECM (i.e. disconnecting battery cables, disconnecting P-1 (blue) ECM connector, etc.) This code should be "cleared" from memory after restoring the ECM's power supply.

CODE 53 - DISTRIBUTOR SIGNAL INTERRUPT

Code 53 indicates that ECM lost distributor signal after engine was started. If distributor reference pulses are interrupted for a short period of time, engine may not stall but code 53 will be stored. If pulses are interrupted for an extended period of time, the engine will stall, code 53 will be stored, and code 12 will be set upon attempting to restart.

If code 53 is stored but does not result in a no start condition, it should be treated as an intermittent code 12.

Code 53 indicates that the ECM lost the distributor signal after the engine was started. If these distributor reference pulses are interrupted for a short period of time, the engine may not stall but Code 53 will be stored. If the pulses are interrupted for an extended period of time, the engine wil1 stall, Code 53 wil1 be stored, and Code 12 will be set upon attempting to restart. If a Code 53 is being stored but does not result in a no start condition, it should be treated as an intermittent Code 12.

Flow Chart, Code 60 - Cruise Control Circuit Transmission Not in Drive. Scheme 118

Flow Chart, Code 60 - Cruise Control Circuit Transmission Not in Drive. Scheme 119

Code 60 indicates that the transmission was not in drive when the Cruise Control was engaged. Whenever the condition which set Code 60 is present, the Cruise Control will disengage.

To begin the diagnosis, perform the switch tests. If Code .7.3 sets, refer to diagnostic CODE 73 . If Code .7.3 passes, then the DFI system is OK. Code 60 was caused by operator error or by an improperly adjusted transmission lever.

Flow Chart, Code 63 - Cruise Control Circuit Set Speed Tolerance Exceeded. Scheme 120

Flow Chart, Code 63 - Cruise Control Circuit Set Speed Tolerance Exceeded (1 Of 2). Scheme 121

Flow Chart, Code 63 - Cruise Control Circuit Set Speed Tolerance Exceeded (2 Of 2). Scheme 122

Code 63 indicates that the Cruise Control was engaged at a certain set speed and the vehicle speed was more than 20 miles per hour above or below this set speed. Whenever the condition which set Code 63 is present, the Cruise Control will disengage.

1. Code 63 may result from operator error or a system malfunction. To diagnose a system malfunction, proceed as follows: A. The engine must be running. B. Turn the engine off and within 2 seconds, turn the ignition on. C. Turn the Cruise Instrument Panel switch to the on position. D. Enter diagnostics and the output cycling tests series 9.6. E. Check the cruise control vacuum and power solenoids to determine if they cycle (click) on and off. If the vacuum and power valves are OK, check for binding linkage. If the linkage is not binding, check for vacuum leaks or blockages. If there are no vacuum problems, then the DFI system is OK.
2. If the vacuum valve does not cycle, disconnect the vacuum valve connector and connect a test light between the harness connector pins while performing the output cycling tests. If there is no light, check circuit 919 or 403 for an open. If the wiring is OK, check for a shorted cruise control vacuum valve. This valve may contain a diode. The properties of a diode are such that current will pass through it in one direction only. Since the polarity of the meter may influence readings when measuring the resistance across the valve (harness disconnected), first measure the resistance in one direction and then reverse the leads of the meter to measure the resistance in the other direction. If both readings are less than 20 ohms, the diode or solenoid is shorted within the valve causing damage to the ECM. Replace both the ECM and the cruise control vacuum valve. If either reading is greater than 20 ohms, the valve is operating normally. Check for a faulty ECM connector or a faulty ECM. If there is a steady light, check circuit 403 for a short to ground. If the circuit is OK, check for a faulty ECM connector or faulty ECM.
3. 3) If the light is on for 3 seconds and off for 3 seconds then the ECM and wiring harness are OK, replace the vacuum valve solenoid. If the power valve does not cycle, disconnect the power valve connector and connect a test light between the harness connector pins while performing the output cycling tests. If there is no light, check circuit 402 for a short to ground. If circuit 402 is shorted damage may have resulted to the ECM. Repair short and check for a damaged ECM beginning at step 1). If circuits 402 and 153 are OK, check for a shorted cruise power valve. This valve may contain a diode. The properties of a diode are such that current will pass through it in one direction only. Since the polarity of the meter may influence readings when measuring the resistance across the valve, (harness disconnected), first measure the resistance in one direction and then reverse the leads of the meter to measure the resistance in the other direction. If both readings are less than 20 ohms, the diode or solenoid is shorted within the valve causing damage to the ECM. Replace both the ECM and the cruise power valve. If either reading is greater than 20 ohms, the valve is operating normally. Check for a faulty ECM connector or a faulty ECM. If there is a steady light, check circuit 402 for a short to voltage. If circuit 402 is OK, check for a faulty ECM connector or faulty ECM. If the light flashes continuously, the ECM and the harness are working properly, replace the power valve solenoid.

CODE 64 - CRUISE CONTROL ACCELERATION EXCEEDED

Code 64 indicates that cruise control was engaged and vehicle acceleration exceeded the preset rate which was programmed into the ECM. If the condition which set code 64 is present, cruise control will disengage. Code 64 could be caused by icy or wet pavement.

Code 64 indicates that the Cruise Control was engaged and the vehicle acceleration exceeded the preset rate which was programmed into the ECM. If the condition which set Code 64 is present, then the Cruise Control will disengage. Code 64 could be caused by icy or wet pavement.

CODE 65 - CRUISE CONTROL COOLANT TEMP EXCEEDED

Code 65 indicates that cruise control was engaged and coolant temperature exceeded a maximum limit. If the condition which set code 65 is present, cruise control will disengage.

Code 65 indicates that the Cruise Control was engaged and the coolant went over temperature. If the condition which set Code 65 is present, then the Cruise Control will disengage. See appropriate ENGINES article in ENGINE MECHANICAL section, if the over temperature condition persists.

CODE 66 - CRUISE CONTROL RPM EXCEEDED

Code 66 indicates that cruise control was engaged and engine speed exceeded a maximum allowable limit. Whenever condition that set code 66 is present, cruise control will disengage. Code 66 can be caused by removing the engine load (shifting transmission out of gear) when cruise control is engaged and operating.

Code 66 indicates that the Cruise Control was engaged and the engine speed exceeded a maximum allowable limit. Whenever the condition which set Code 66 is present, the Cruise Control will disengage. Code 66 can be caused by removing the engine load (placing the gear selector in neutral) when the cruise control is engaged and operating.

Flow Chart, Code 67 - Cruise Control Shorted Set or Resume Circuit. Scheme 123

Flow Chart, Code 67 - Cruise Control Shorted Set or Resume Circuit. Scheme 124

Code 67 indicates that the set/coast or resume/acceleration switches were improperly set when Cruise Control was engaged. Whenever the condition which set Code 67 is present, the Cruise Control will not operate during that ignition cycle.

To diagnose the system perform the switch tests. If codes .7.6 or .7.7 set refer to the appropriate diagnostic chart. If codes .7.6 and .7.7 of the switch tests pass, then the DFI system is OK. Code 67 was caused by a failure in the set/coast or resume/acceleration circuits which was present when the cruise instrument panel switch was turned on.

Flow Chart, Code 71 - Cruise Control Brake Circuit. Scheme 125

Flow Chart, Code 71 - Cruise Control Brake Circuit. Scheme 126

The Cruise Control brake circuit sends a 12 volt signal to the ECM except when the brake is depressed. When the brake is depressed, the switch is opened and the brake signal drops to 0 volts.

1. Code .7.1 indicates the brake signal doesn't switch from 12 volts to 0 volts when the brake is applied. With the ignition on backprobe the Cruise Control brake switch connector circuits 904 and 919 with a test light connected to ground on each circuit. If the test light lights on only one side of the switch, then the Cruise Control brake switch does not have continuity and should be replaced if it is properly adjusted.
2. If there is a light on both sides of the Cruise Control brake switch, then the switch has continuity. With the ignition on, depress the brake pedal and backprobe the Cruise Control brake switch circuit 919 with a test light to ground. If the test light continues to glow replace the Cruise Control brake switch because it is shorted.
3. If the test light does not glow, then the switch is functioning properly. Check circuit 919 for an open. If circuit 919 is OK, check for a faulty ECM connector or faulty ECM because it is not processing a good brake release signal.
4. Check the 3 amp cruise fuse. If it is OK, then repair an open in circuit 904.
5. If the Cruise Control fuse is not OK, then there is a short circuit to ground in the wiring harness or the ECM. Check circuits 904 and 919 for a short to ground. Engaging the cruise instrument panel switch the set/resume switch, or the resume/ acceleration switch can blow the cruise fuse. This situation would occur if circuits 903, 916, or 917 have a short to ground on them. If the wiring harness is OK and the fuse blows again, check for a faulty ECM connector or faulty ECM because it is internally shorted.

Flow Chart, Code 72 - Throttle Switch Circuit. Scheme 127

Flow Chart, Code 72 - Throttle Switch Circuit. Scheme 128

The ECM supplies a 12-volt signal to the ISC motor pin B. When the engine is at idle speeds, the throttle linkage contacts the ISC plunger and closes the throttle switch whicl1 pulls the voltage on the ISC motor pin B to 0 volts.

Note. Only ISC pins C and D should have voltage applied to them. Jumpering ISC pins A and B will cause ISC motor damage. It may be desirable to make the jumper leads for this test from a 4-way weatherpack connector.

Reconnect the ISC motor connector and rerun the switch tests.

1. Code .7.2 indicates that the throttle switch is malfunctioning. With the ignition on and Code .7.2 displayed, physically push the actuator plunger into its stop. If this results in Code .7.2 passing, check for mechanical binding in the throttle linkage such as throttle blades, shafts, throttle cable, Cruise Control linkage, TV cable, throttle position sensor, or throttle return springs. Also check the minimum air rate adjustment which may be holding the throttle open. The binding linkage is preventing the throttle switch from closing.
2. If Code .7.2 remains, check the ISC plunger and the idle switch for minding in the fully retracted position. IF the ISC plunger is binding, disconnect the ISC motor and extend the plunger by momentarily jumpering 12 volts to pin D of the ISC motor and jumpering pin C to ground. Reconnect the ISC motor connector and rerun the switch tests. NOTE: Only ISC pins C and D should have voltage applied to them. Jumpering ISC pins A and B will cause ISC motor damage. It may be desirable to make the jumper leads for this test from a 4-way weatherpack connector.
3. With ignition on and Code .7.2 displayed, disconnect the ISC motor and momentarily jumper harness pins A and B together. If Code .7.2 disappears, then replace the ISC motor.
4. If Code .7.2 remains, then the problem is in the wiring harness or the ECM. To identify the defective component, measure the voltage on harness pin B with the ignition on. If the voltage is 12 volts, then check circuit 450 for an open. If circuit 450 has continuity, then check for a faulty ECM connector or faulty ECM. If the voltage is less than 1 volt, then check circuit 427 for an open or short to ground. If circuit 427 is OK, check for a faulty ECM connector or faulty ECM because it is not providing the required 12 volt signal.

Flow Chart, Code 73 - Drive (ADL) Circuit. Scheme 129

Flow Chart, Code 73 - Drive (ADL) Circuit. Scheme 130

When the transmission is operating in drive, the ADL switch is closed, and the switch supplies a 12 volt signal to the ECM.

1. Code .7.3 indicates that the ECM is not receiving the 12 volt signal when the transmission is in drive. Begin the diagnosis by checking the 20 amp body fuse. If the fuse is blown, check circuits fed by body fuses for a short to ground. Repair the wiring, replace the fuse, and rerun the switch tests.
2. If the 20 amp body fuse is OK, check the adjustment of the drive switch. The switch should open as the linkage is shifted from drive to neutral. If the adjustment is OK, turn the ignition on and enter diagnostics. While displaying Code .7.3, disconnect the drive switch and jumper the harness pins together. If Code .7.3 disappears after the jumper is removed, the ECM and the wiring harness are operating properly, therefore, the drive switch is defective.

Note. If Code .7.3 remains, then check circuits 243 and 340 for an open. If circuits 243 and 340 are OK, check for 12 volts on the body fuse. If the 12 volt signal is present, check for a faulty ECM connector or faulty ECM. If the body fuse does not have 12 volts on it, look for an open in the harness which leads to the body fuse.

Flow Chart, Code 74 - Reverse Circuit. Scheme 131

Flow Chart, Code 74 - Reverse Circuit. Scheme 132

When the transmission is operating in reverse, the backup light switch is closed, and the switch supplies a 12 volt signal to the ECM.

Code .7.4 indicates that the ECM is not receiving the 12 volt signal when the transmission is in reverse. To begin the diagnosis, check the backup lamps for proper operation. If the backup lamps do not operate properly, refer to the appropriate WIRING DIAGRAM. If the backup lamps function properly, then the backup fuse and circuit 75 are OK. Check circuit 24 for an open circuit. If circuit 24 is OK, check for a faulty ECM connector or faulty ECM.

Flow Chart, Code 75 - Cruise On/Off Circuit. Scheme 133

Flow Chart, Code 75 - Cruise On/Off Circuit. Scheme 134

The cruise instrun1ent panel switch sends a 12 volt signal to the ECM when the switch is in the on position. When the cruise switch is turned off, the voltage on the P3 (ORN) ECM connector pin E drops to 0 volts.

1. Code .7.5 indicates that 3 the ECM is not receiving the 12 volt signal from the cruise instrument panel switch when cruise is enabled. Retest the switch function. To begin the diagnosis, turn the ignition on and the cruise enable switch off. Measure the voltage on the P-3 (orange) ECM connector pin E with the voltmeter (part no. J-29125) connected to ground. If the voltmeter reads 12 volts, then disconnect the P-3 (orange) ECM connector and measure the voltage on pin E again. If the voltage is still 12 volts, then check circuit 903 for a short to voltage. If the wiring is OK, replace the cruise instrument panel switch. If the voltage on pin E reads 0 volts, then check for a faulty ECM connector or faulty ECM.
2. If the voltage is 0 volts, then turn the cruise enable switch on and measure the voltage at the P-3 (orange) ECM connector pin E. If the voltmeter reads 12 volts then check for a faulty ECM connector or faulty ECM because it is unable to process the proper signal.
3. The ECM is operating properly at this time and the problem is in the harness or in the instrument panel switch. To isolate the problem, measure the voltage at pin C of the cruise instrument panel switch. If the voltmeter reads 0 volts, then circuit 904 is open or shorted to ground.
4. If the voltage on pin C of the instrument panel switch reads 12 volts, then check circuit 903 for an open or short to ground. If circuit 903 is OK, replace the cruise instrument panel switch because it is open.

Flow Chart, Code 76 - Cruise Set/Coast Circuit. Scheme 135

Flow Chart, Code 76 - Cruise Set/Coast Circuit. Scheme 136

The Cruise Control set/coast switch sends a 12 volt signal to the ECM when the set/coast switch is depressed.

1. Code .7.6 indicates that the ECM is not receiving the 12 volt signal from the set/coast switch when it is depressed. Rerun the switch test. To begin the diagnosis, turn the ignition on and the cruise enable switch on. Connect a voltmeter (J-29125) to the P-3 (orange) ECM connector pin F and ground.
2. If the voltage of pin F reads 12 volts, disconnect the P-3 (orange) ECM connector and measure the voltage on pin F again. If the voltage reads 12 volts, check circuit 917 for a short to voltage. If circuit 917 is OK, replace the set/coast switch. If the voltage on pin F is 0 volts, check for a faulty ECM connector or faulty ECM.
3. While depressing the set/coast switch, measure the voltage on the P-3 (orange) ECM connector pin F again. If the voltage is 0 volts, check circuit 917 for an open or short to ground and circuit 903 for an open. If circuits 917 and 903 are OK, replace the set/coast switch. If the voltage on pin F is 12 volts, then check for a faulty ECM connector or faulty ECM because it is not processing the 12 volt signal.

Flow Chart, Code 77 - Cruise Resume/Accel. Circuit. Scheme 137

Flow Chart, Code 77 - Cruise Resume/Accel. Circuit. Scheme 138

The Cruise Control resume/acceleration switch sends a 12 volt signal to the ECM when the resume/acceleration switch is depressed.

1. Code .7.7 indicates that the ECM is not receiving the 12 volt signal from the resume/acceleration switch when it is depressed. Rerun the switch test. To begin the diagnosis, turn the ignition on and the cruise enable switch on. Connect a voltmeter (J-29125) to the P-3 (orange) ECM connector pin D and ground.
2. If the voltage on pin D reads 12 volts, disconnect the P-3 (orange) ECM connector and measure the voltage on pin D again. If the voltage reads 12 volts, check circuit 916 for a short to voltage. If circuit 916 is OK, replace the resume/acceleration switch. If the voltage on pin D is 0 volts, check for a faulty ECM connector or faulty ECM.
3. While depressing the resume/acceleration switch, measure the voltage on the P-3 (orange) ECM connector pin D again. If the voltage is 0 volts, check circuit 916 for an open or short to ground and circuit 903 for an open. If circuits 916 and 903 are OK, replace the resume/acceleration switch. If the voltage on pin D is 12 volts, then check for a faulty ECM connector or faulty ECM because it is not processing the 12 volt signal.

Flow Chart, Code 78 - Instant/Average Circuit. Scheme 139

Flow Chart, Code 78 - Instant/Average Circuit. Scheme 140

The "instant/average" data request line, circuit 477, is connected to ground by pushing the button on the Fuel Data panel.

1. Code .7.8 indicates that the ECM is not receiving a 0 voltage signal when the average button is depressed. To diagnose this condition, turn the ignition on and display Code .7.8. Remove the Fuel Data panel connector and momentarily jumper harness pin D to ground. This action simulates the operation of the "instant/average" button and, if Code .7.8 disappears, the ECM is operating properly. Check circuit 990, the ground dine, for an open. If circuit 990 is OK, check for a faulty Fuel Data connector or faulty Fuel Data panel.
2. If Code .7.8 remains after grounding harness pin D, then check circuit 477 for an open or short to ground. If circuit 477 is OK, check for a faulty ECM com1ector or faulty ECM.

Flow Chart, Code 79 - "Reset" Circuit. Scheme 141

Flow Chart, Code 79 - "Reset" Circuit. Scheme 142

The "reset" line, circuit 464, is connected to ground by pushing the "reset" button on the Fuel Data panel.

1. Code .7.9 indicates that the ECM is not receiving a 0 voltage signal when the reset button is depressed. To diagnose this condition, turn the ignition on and display Code .7.9. Remove the Fuel Data panel connector and momentarily jumper harness pin E to ground. This action simulates the operation of the "reset" button and, if Code .7.9 disappears, the ECM is operating properly. Check circuit 990, the ground line, for an open. If circuit 990 is OK, check for a faulty Fuel Data connector or faulty Fuel Data panel.
2. If Code .7.9 remains after grounding harness pin E, then check circuit 464 for an open or short to ground. If circuit 464 is OK, check for a faults ECM connector or faulty ECM.

Flow Chart, Code 80 - Air Conditioning Clutch Circuit. Scheme 143

Flow Chart, Code 80 - Air Conditioning Clutch Circuit. Scheme 144

The ECC control head grounds a 12 volt signal from the power module to signal the enabling of the compressor clutch. This signal (circuit 977) is sent to the ECM so that the ECM can compensate for the additional air conditioning load on the engine.

1. Code .8.0 indicates that the ECM is not able to detect the signal when the air conditioning clutch turns on. With the engine running and with the ECC set at 60, enter diagnostics. If the A/C clutch does not engage with the "A/C Clutch" status light on, then follow the ECC diagnosis procedure for COMPRESSOR NOT ENGAGED. If the compressor engages with the status light on but does not disengage when the status light is turned off then follow the ECC diagnosis procedure for COMPRESSOR ENGAGED IN ECONOMY.
2. If the compressor is working properly then measure the voltage at P-2 (red) ECM connector Pin 2l with the A/C CLUTCH status light off. If the voltage is 0 volts, then circuit 977 is open to the ECM. If the voltage is 12 volts the fault must be in the ECM connector or ECM because it is unable to process a good signal.

Performance Chart No. 1 - No Start or Stall After Start. Scheme 145

All internal combustion engines require spark, fuel, and proper timing to operate. DFI is no different. The first step should be to determine which of these three elements is missing.

1. The diagnosis of a NO START condition should begin by using the DFI self-diagnostics. If trouble codes 12, 16, 20 or 51 are stored hard, follow the appropriate chart to repair the malfunction. If the display reads "..", check the 15 amp ECS fuse and the 20 amp battery fuse. If either fuse is blown, check the affected circuit for a short to ground. If circuit is OK and the fuse blows again, check for a faulty ECM connector or faulty ECM.
2. If the fuses are OK, then check circuits 439 and 480 for an open. If circuits 439 and 480 are OK and if the engine will not start, then the PROM and ECM must be investigated for faulty connections or internal malfunctions.
3. To check the integrity of the injectors, they should be checked for being stuck open or leaking. Allow the ECM to power-down with the ignition off for 10 seconds. At ignition on (engine not running), the fuel pump wil1 be energized for 2 seconds. If any spray or leakage is observed, refer to «CHART 6 - INJECTOR SYSTEM»(/cadillac/fleetwood/75-series-1956-1992/remont/testing-diagnostics/#dfi-tests-wcodes) .
4. The actual fuel delivery system should be checked by observing the spray from both injectors while the engine is cranking If only one injector is spraying, refer to «CHART 6 - INJECTOR SYSTEM»(/cadillac/fleetwood/75-series-1956-1992/remont/testing-diagnostics/#dfi-tests-wcodes) . If no injector is spraying, refer to «CHART 4 - FUEL SYSTEM»(/cadillac/fleetwood/75-series-1956-1992/remont/testing-diagnostics/#dfi-tests-wcodes) .
5. To determine if spark is available, connect a ST-125 spark tester (J-26792) to any convenient spark plug wire and crank the engine. If a no spark condition exists, there is a defect in the HEI system. Refer to the HEI diagnosis.
6. If spark is available at the spark plug wire, then the spark timing circuit of the ECM could prevent the engine from running. To check spark timing, open the set timing connector and crank the engine. Opening the set timing connector forces the HEI system into the bypass mode which means that the HEI module provides 10° of spark advance at all times and disregards the ECM's spark advance signal. If the ECM's spark advance signal is the cause of the no start condition, then its effect can be eliminated by forcing the HEI module into the bypass mode. If the car now starts in the bypass mode, then the HEI module is not receiving an ECM spark timing signal due to a problem with the harness or the ECM itself. Check circuit 423, the EST line, for a short to ground. If circuit 423 is OK, then check for a faulty ECM connector or faulty ECM since it is not supplying the spark timing to the HEI module.
7. Spark and spark timing are present; therefore, the fuel system must be checked next. Connect the fuel pressure gauge (part no. J-25400-300) and observe the fuel pressure while cranking. The gauge should be installed in the fuel inlet line at the service fitting. A fuel pressure reading of between 9-12 PSI during cranking indicates that the fuel system is operating properly. Improper fuel pressure indicates a fuel problem, refer to «CHART 4 - FUEL SYSTEM»(/cadillac/fleetwood/75-series-1956-1992/remont/testing-diagnostics/#dfi-tests-wcodes) .

Performance Chart No. 2 - "Service Now" &/or "Service Soon" Lights on - No Hard Codes. Scheme 146

The "Service Soon" and "Service Now" lights are powered from the ignition switch through the 20 amp gauge fuse and circuit 39.

1. The ECM supplies ground to the "Service Now" light through circuit 419. If this wire is shorted to ground, the "Service Now" light will be on whenever the ignition switch is on. No vehicle performance problems are caused by a shorted circuit 419.
2. The ECM supplies ground to the "Service Soon" light through circuit 499. If this wire is shorted to ground, the "Service Soon" light will be on whenever the ignition switch is on. No vehicle performance problems are caused by a shorted circuit 499.
3. Both the "Service Soon" and "Service Now" lights will be on with no codes set if the diagnostic request line, circuit 451, is shorted to ground. Both lights will also stay on if there is a short to voltage on the crank signal input to the ECM (circuit 6).
4. If all the wiring circuits are OK. then the PROM and ECM must be investigated for faulty connections or internal malfunctions.

Performance Chart No. 3A - "Service Now" Light Inoperative. Scheme 147

1. The "Service Now" light bulb check is performed when the engine is cranking. circuit 39 supplies voltage to the "Service Now" light, the "Service Soon" light and the coolant temperature light. If the coolant light is also inoperative, a problem probably exists in circuit 39. Observe the coolant light with ignition on and the engine not running (after a 10 second ignition off power-down).
2. If all three lights are inoperative, check the condition of the gauge fuse. If it is blown, check circuit 39 for a short to ground. If the gauge fuse is OK, measure the voltage at the gauge fuse with the ignition on. If the fuse has 12 volts on it repair circuit 39 for an open. If voltage is not available at the fuse, the open circuit must be between the ignition switch and the fuse, repair as required.
3. If the coolant light operates normally, the power circuit (39) is OK and the cause of the problem is the bulb or the ground side of the bulb. The ECM is responsible for turning on the "Service Now" light by grounding circuit 419. The ECM's activity can be simulated by grounding circuit 419 witl1 a jumper lead at pin D of the ALDL diagnostic connector. If the light comes on, check circuit 419 for an open to the ECM. If circuit 419 is OK, check for a faulty ECM connector or faulty ECM. If the bulb does not light, the cause is a burned out bulb or an open in circuit 419.

Performance Chart No. 3B - "Service Soon" Light Inoperative. Scheme 148

1. The "Service Soon" light bulb check is performed when the engine is cranking. circuit 39 supplies voltage to the "Service Soon" light, the "Service Now" light and the coolant temperature light. If the coolant light is also inoperative, a problem probably exists in circuit 39. Observe the coolant light with ignition on and the engine not running (after a 10 second ignition off power-down).
2. If all three lights are inoperative, check the condition of the gauge fuse. If it is blown, check circuit 39 for a short to ground. If the gauge fuse is OK, measure the voltage at the gauge fuse with the ignition on. If the fuse has 12 volts on it repair circuit 39 for an open. If voltage is not available at the fuse, the open circuit must be between the ignition switch and the fuse, repair as required.
3. If the coolant light operates normally, the power circuit (39) is OK and the cause of the problem is the bulb or the ground side of the bulb. The ECM is responsible for turning on the "Service Soon" light by grounding circuit 499. If the "Service Soon" light remains off during crank, repair a burned-out bulb or an open in circuit 499. If the bulb and circuit are OK, check for a faulty ECM connector or a faulty ECM.

Performance Chart No. 4 - Fuel System Diagnosis. Scheme 149

1. Fuel system diagnosis should begin by determining if the fuel pump is operating properly. The fuel pressure gauge (part no. J-25400-300) should be installed at the fuel line service fitting. Measure the fuel pressure while cranking the engine. If the fuel pressure is between 9 and 12 PSI, then refer to the performance diagnosis «CHART 6 - INJECTOR SYSTEM»(/cadillac/fleetwood/75-series-1956-1992/remont/testing-diagnostics/#dfi-tests-wcodes) .
2. If the fuel pressure is less than 9 PSI and if there are no codes set, then the fuel pump relay and the ECM are OK. Turn the ignition off and disconnect the 6-way weatherpack connector at the tail panel. Probe harness pin C with a voltmeter (part no. J-29125) as the ignition is turned on. If the voltage on pin C does not go to 12 volts for 2 seconds, then repair circuit 120 for an open.
3. A fuel delivery system problem exists because the fuel pump signal at the tail panel is OK. Disconnect the fuel return line at the throttle body and install a plug in the throttle body opening. This procedure eliminates the pressure regulator from the fuel delivery circuit. If the pump is able to produce more than 9 PSI with the pressure regulator out of the circuit, replace the pressure regulator because it is holding the pressure below 9 PSI.
4. If the fuel pressure remains below 9 PSI with the return line plugged, a restriction may exist in the fuel supply line. A restricted fuel supply line should be checked visually for kinks, damage, etc. the fuel filter element can also restrict fuel flow. If the fuel lines and fuel filter are OK, replace the fuel pump.
5. Fuel pressure above 12 PSI is caused either by a malfunction of the pressure regulator or by a restriction in the fuel return line. To isolate the cause of the high fuel pressure, disconnect the fuel return line at the throttle body and connect a suitable fitting to the throttle body which will accept a length of flexible rubber fuel hose. Insert the other end of the hose into a suitable fuel container and observe the fuel pressure as the ignition switch is turned on. If the fuel pressure remains above 12 PSI, replace the pressure regulator since it is unable to control the pressure properly. If the fuel pressure drops into the correct pressure range of 9-12 PSI, the fuel return line is restricted. A restricted fuel return line can be located by visually inspecting the line for kinks, damage, etc.

Performance Chart No. 5 - Poor Performance &/or Poor Fuel Economy. Scheme 150

1. Poor performance and/or poor fuel economy diagnosis begins by determining if the fuel system is operating properly. Refer to the performance diagnosis «CHART 4 - FUEL SYSTEM»(/cadillac/fleetwood/75-series-1956-1992/remont/testing-diagnostics/#dfi-tests-wcodes) .
2. If the fuel system is operating correctly, then the ignition timing should be checked. Open the set timing connector and check timing. Base (initial) timing should be 10° BTDC (800 RPM or less). If it isn't at 10°, reset the timing to 10°.
3. Once it has been established that the base timing is correct, the system's ability to advance spark must be determined. Since the ECM determines ignition advance based on many variables, it is not possible to establish timing checkpoints. It is only important to know that the ECM increased the spark advance. Therefore, it should be assumed that the advance curve supplied by the ECM is correct. With the set timing connector reconnected, the spark timing should be between 20° and 30° BTDC at idle speed.
4. If the ignition timing doesn't advance, there is a problem with the advance system. When the voltage on the HEI bypass line, circuit 462, is 0 volts, the HEI module is forced into bypass mode which means that the HEI module provides 10° of spark advance at all times and disregards the spark advance signal from the ECM. If the voltage on the HEI bypass line is 5 volts, the HEI module accepts the spark timing signal provided by the ECM. From the above description, it can be seen that the ECM advances the spark timing based on the voltage on the HEI bypass line, circuit 462 (no voltage = base timing; 5 volts = EST). If the voltage is greater than 4 volts, replace the HEI module because the ECM is supplying the proper bypass signal but the HEI module is not processing it. A voltage which is less than 1 volt indicates that the ECM is not producing the bypass signal of 5 volts, therefore replace the ECM.
5. Since EGR can affect the air/fuel ratio, its operation should be checked using the EGR system tests described in the performance diagnosis «CHART 7»(/cadillac/fleetwood/75-series-1956-1992/remont/testing-diagnostics/#dfi-tests-wcodes) . Check the operation of the air management system to assure that the flow is not directed to the exhaust ports after warm-up. See «CHART 8»(/cadillac/fleetwood/75-series-1956-1992/remont/testing-diagnostics/#dfi-tests-wcodes) . A restricted air cleaner can also affect the vehicle's performance. Check for binding of T.V. cable, throttle return spring or throttle position sensor. Check for vacuum leaks around the intake manifold or in1 the vacuum hose routing. Enter diagnostic series .9.0. Check parameters to verify that al1 sensors are in their normal operating range.
6. Refer to appropriate article in ENGINE PERFORMANCE section for specific service procedures on engine mechanical check-out. (i.e. Compression check, camshaft timing. fouled/cracked plugs, bad spark plug wires).

Performance Chart No. 6 - Injector System Diagnosis. Scheme 151

1. If this procedure is being followed for a "no-start" condition, crank the engine for 5 seconds to check the distributor reference signal. If a Code 12 does not set, turn the ignition off for 10 seconds and observe the injectors as the ignition is turned back on. If there is no spray, then they are not stuck open. Observe the injectors while cranking the engine.
2. To determine if the injector is being activated electrically, repeat the above procedure with the electrical connector removed. If the injector continues to spray, it is defective and must be replaced. If the injector no longer sprays, the drive circuit of the affected injector must either be shorted to ground or the ECM is grounding internally.
3. If both injectors spray or if neither injector sprays, it must be determined whether the fuel system is operating properly. The fuel pressure gauge (part no. J-25400-300) should be installed at the fuel line service fitting. Measure the fuel pressure while cranking the engine. If the fuel pressure is not between 9-12 PSI, then refer to performance diagnosis «CHART 4 - FUEL SYSTEM»(/cadillac/fleetwood/75-series-1956-1992/remont/testing-diagnostics/#dfi-tests-wcodes) .
4. If the 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 the injector fuses then the ECM must be faulty because it is failing to ground both injector circuits. If there is no voltage at the fuse, check for voltage at the 15 amp ECS fuse which feeds the injector fuses. If there is voltage here then an open must exist between the fuses on circuit 439. If there is no voltage at the ECS fuse then circuit 3 must be repaired for an open or short to ground.
5. If the fuel pressure is between 9-12 psi and there was fuel spray from both injectors while cranking, then check the injector system to determine if the injectors leak with the system pressurized. If the fuel is dripping, check for damaged "O" rings or replace the injector. If the fuel does not drip, then the fuel system is OK.
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. The malfunction can be isolated by switching the injector connectors. If the problem remains with the original injector after switching the connector, then the injector is defective. Replace the injector.
7. If the problem moves with the injector connector, then the problem is an improper signal in the injector circuits. Circuits 481 and 482 supply a 12 volt power signal to the injectors. The ECM energizes the injectors by supplying a ground path to the injectors through circuits 467 and 468. Check the 3 amp injector fuses by visually inspecting the fuse filaments. If the fuses are OK, check circuits 467, 468, 481 and 482 for an open. If these circuits are OK, check circuit 450A to see that it is providing a ground to Pin 6 of the P-2 (red) ECM connector. If the ECM does not receive a ground on circuit 450A it will only fire one of the two injectors. If circuit 450A is OK check for a faulty ECM connector or faulty ECM because it is unable to supply a ground path for one of the injectors.
8. If the 3 amp injector fuse is blown, check circuits 467, 468, 481 and 482 for a short to ground. If these circuits are OK and if the fuse blows again, check for a faulty ECM connector or faulty ECM.

Performance Chart No. 7 - EGR Diagnosis. Scheme 152

1. EGR diagnosis begins on a fully warmed-up engine (coolant temperature parameter .0.4, 85°C or greater) by checking for movement of the EGR diaphragm as engine speed is quickly accelerated from idle to approximately 2000 RPM.
2. If the diaphragm goes up as the RPM is increased, verify that the EGR flow passages are clear and the EGR valve is functioning properly by pushing up on the underside of the EGR valve, to manually open it, when the engine is idling. Note any change in engine RPM. If the engine RPM remains constant, check for plugged EGR flow passages or a defective valve
3. If there is no movement in the EGR diaphragm as the engine speed is quickly accelerated from idle to 2000 RPM, check for a faulty electrical circuit, Disconnect the EGR connector from the control solenoid and install a test light between the harness connector pins and enter diagnostic series .9.6 (output cycling mode). If there is no light, check circuit 639 for a short to ground or circuits 639 and 831 for an open circuit. If the wiring is OK, check for a shorted EGR solenoid, This solenoid may contain a diode. The properties of a diode are such that current will pass through it in one direction only. Since the polarity of the meter may influence readings when measuring the resistance across the solenoid, (harness disconnected), measure the resistance in one direction and then reverse the leads of the meter to measure the resistance in the other direction. If both readings are less than 20 ohms, the diode or solenoid is shorted within the solenoid causing damage to the ECM. Replace both the ECM and the EGR solenoid. If either reading is greater than 20 ohms, the solenoid is operating normally, Check for a faulty ECM connector or a faulty ECM. If there is a steady light, check circuit 831 for a short to ground, If circuit 831 is OK, check for a faulty ECM connector or a faulty ECM. If the test light turns on and off at 3 second intervals then the ECM and the harness are working properly, but either the EGR control solenoid or the EGR valve could be at fault.
4. If the light turns on and off every 3 seconds reconnect the solenoid connector, disconnect the EGR valve vacuum supply and connect a vacuum gauge to the supply line. Check for a change in the vacuum level as engine speed is quickly accelerated from idle to approximately 2000 RPM. If the vacuum level never goes below 3.0 in.hg. replace the EGR solenoid. If the vacuum level never goes above 7.0 in, hg,: make a final check of the vacuum hoses for restrictions or leaks. If the vacuum hoses are OK, replace the EGR control solenoid. If the vacuum level goes above 7.0 in.hg. and goes below 3.0 in.hg. replace the EGR valve.

Performance Chart No. 8 - Air Management Diagnosis. Scheme 153

1. Air management diagnosis begins by determining whether the air management valve is receiving air through the air pump delivery hose and whether the air is being properly channeled to the locations commanded. On a cold running engine (coolant temperature, parameter.0 4, 70°C or less), disconnect the exhaust port hose from the switch valve Check for air flow from the switch valve to the exhaust ports.
2. If no air flows to the exhaust port when the engine is cold, check for proper vacuum supply at the switching and divert valves. Otherwise, check for air flow through the air pump delivery hose.
3. Once the engine has fully warmed-up (coolant temperature parameter .0.4, 85°C or greater): disconnect the converter hose from the switch valve and check for air flow from the switch valve to the converter port.
4. If there is no air flow to the converter port, check for a faulty switching valve by disconnecting the air switch connector and installing a test light between the harness connector pins. Enter diagnostic series .9.6 (output cycling mode). If there is no light, check circuits 639 and 436 for an open circuit or circuit 639 for a short to ground If circuits 639 and 436 are OK, check for a shorted AIR switching solenoid. This solenoid may contain a diode. The properties of a diode are such that current will pass through it in one direction only. Since the polarity of the meter may influence resistance readings when measuring the resistance across the solenoid (harness disconnected), first measure the resistance in one direction and then reverse the leads of the meter to measure the resistance in the other direction. If both readings are less than 20 ohms, the diode or solenoid is shorted within the solenoid causing damage to the ECM. Replace both the ECM and the AIR switching solenoid. If either reading is greater than 20 ohms, the valve is operating normally. Check for a faulty ECM connector or a faulty ECM. If there is a steady light, check circuit 436 for a short to ground. If circuit 436 is OK, check for a faulty ECM connector or a faulty ECM.
5. To verify that the divert valve is operable on a fully warmed up engine, check for air flow from the divert valve port at the air cleaner by momentarily depressing the throttle lever. When the engine is accelerated (or decelerated) quickly, the air is sent (diverted) to the air cleaner to prevent backfiring.
6. Check for a faulty divert valve by disconnecting the valve connector and installing a test light between the harness connector pins and enter diagnostic series .9.6 (output cycling mode). If there is no light, check circuits 639 and 439 for an open circuit. If circuits 639 and 429 are OK, check for a shorted AIR divert solenoid. This solenoid may contain a diode. First measure the resistance in one direction and then reverse the leads of the meter to measure the resistance in the other direction. If both readings are less than 20 ohms, the diode or solenoid is shorted within the solenoid causing damage to the ECM. Replace both the ECM and the AIR divert solenoid. If either reading is greater than 20 ohms, the solenoid is operating normally. Check for a faulty ECM connector or a faulty ECM. If there is a steady light, check circuit 428 for a short to ground. If circuit 429 is OK, check for a faulty ECM connector or a faulty ECM. If the test light turns on and off at 3 seconds intervals, then the ECM and the harness are working properly, replace the air management valve.

Performance Chart No. 9 - Canister Purge Diagnosis. Scheme 154

1. Canister purge control diagnosis begins by determining if vacuum is being properly supplied to the canister. When the engine is cold and operating in the open loop mode, there should be no vacuum (zero reading on the vacuum gauge) at the canister during idle.
2. With engine running at normal operating temperature, and the system in closed loop mode there should be vacuum at the canister during idle.
3. If the opposite condition exists in either of the previous steps 1) or 2), check for a faulty electrical circuit. Disconnect the canister purge connector and install a test light between the harness connector pins. Enter diagnostic series .9.6 (output cycling mode). If there is no light, check circuits 639 for a short to ground or circuits 639 and 428 for an open circuit. If circuits 639 and 428 are OK, check for a shorted canister purge solenoid. This solenoid may contain a diode. The properties of a diode are such that current will pass through it in one direction only. Since the polarity of the meter may influence resistance readings. When measuring the resistance across the solenoid (harness disconnected), first measure the resistance in one direction and then reverse the leads of the meter to measure the resistance in the other direction. If both readings are less than 20 ohms, the diode or solenoid is shorted within the solenoid causing damage to the ECM. Replace both the ECM and the canister purge solenoid. If either reading is greater than 20 ohms, the solenoid is operating normally. Check for a faulty ECM connector or a faulty ECM. If there is a steady light. check circuit 498 for a short to ground. If circuit 428 is OK, check for a faulty ECM connector or a faulty ECM. If the test light turns on and off at 3 second intervals. then the ECM and the harness are working properly. Make a final check of the vacuum hoses for restrictions or leaks. If the hoses are OK. replace the canister purge solenoid.

Performance Chart No. 10 - No Cruise Control. Scheme 155

1. Whenever the condition of NO CRUISE CONTROL exists, the diagnosis should begin by entering diagnostics and noting the "hard" failures. Any 60 series code should be considered a hard failure, however, 60 series codes can be caused by operator error. If trouble codes are set, refer to the appropriate diagnosis chart.
2. Perform switch tests. If any of the codes set and will not disappear, it is important to repair these malfunctions because these switches provide inputs to the ECM. Without these inputs, the Cruise Control will disengage.
3. To diagnose a system malfunction, proceed as follows: A. The engine must be running B. Turn the engh1e off and within 2 seconds, turn the ignition on. C. Turn the cruise instrument panel switch to the ON position. D. Enter diagnostics and the output cycling tests series 9.6. E. Check the Cruise Control vacuum and power solenoids to determine if they cycle (click) on and off. If the vacuum and power valves are OK, check for binding linkage. If the linkage is not binding, check for vacuum leaks or blockages. If there are no vacuum problems, then the DFI system is OK.
4. If the vacuum valve does not cycle, disconnect the vacuum valve and connect a test light between the harness connector pins while performing the output cycling tests. If there is no light, check circuits 919 or 403 for an open. If the wiring is OK, check for a shorted cruise control vacuum valve. This valve may contain a diode. The properties of a diode are such that current will pass through it in one direction only. Since the polarity of the meter may influence readings when measuring the resistance across the valve (harness disconnected), first measure the resistance in one direction and then reverse the leads of the meter to measure the resistance in the other direction. If both readings are less than 20 ohms, the diode or solenoid is shorted within the solenoid causing damage to the ECM. Replace both the ECM and the cruise control vacuum valve. If either reading is greater than 20 ohms, the valve is operating normally. Check for a faulty ECM connector or a faulty ECM. If there is a steady light, check circuit 403 for a short to ground. If the circuit is OK, check for a faulty ECM connector or faulty ECM. If the light is on for 3 seconds and off for 3 seconds, then the ECM and wiring harness are OK, replace the vacuum valve solenoid.
5. If the power valve does not cycle, disconnect the power valve and connect a test light between the harness connector pins while performing the output cycling tests. If there is no light, check circuit 402 for a short to ground. If circuit 402 is shorted, damage to the ECM may have resulted. Repair the short and check for a damaged ECM beginning at step 1). If the circuits 402 and 151 are OK, check for a shorted cruise power valve. This valve may contain a diode. The properties of a diode are such that current will pass through it in one direction only. Since the polarity of the meter may influence readings when measuring the resistance across the valve (harness disconnected), first measure the resistance in one direction and then reverse the leads of the meter to measure the resistance in the other direction. If both readings are less than 20 ohms, the diode or solenoid is shorted within the valve causing damage to the ECM. Replace both the ECM and the cruise power valve. If either reading is greater than 20 ohms, the valve is operating normally. Check for a faulty ECM connector or a faulty ECM. If there is a steady light, check circuit 402 for a short to voltage. If circuit 402 is OK, check for a faulty ECM connector or faulty ECM. If the light flashes continuously, then the ECM and the harness are working properly, replace the power valve solenoid.

Performance Chart No. 11A - Blank Fuel Data Display. Scheme 156

The ECC control head is an integral part of the Fuel Data display system. The ECM determines the fuel consumption based on vehicle speed and on the amount of fuel delivered to the engine. This information is sent to the ECC control head through the serial data line, circuit 461. The ECC control head interprets this information and illuminates the proper segments of the Fuel Data display panel.

1. If the ECC allows blower operation in the "defrost" mode then the ECC is working properly and the ground to the Fuel Data panel must be checked. circuit 990 is the ground wire which causes a blank Fuel Data display when it is open. Repair circuit 990 if it is open.
2. The Fuel Data information transmitted by the ECM through circuit 461 is a constantly changing voltage signal. It is possible to monitor this pulsing voltage by backprobing control head pin 3, circuit 461 with a voltmeter (part no. J-29125).
3. If the voltage is not pulsating between 2 and 4 volts, then remove the ECC control head connector and probe control head pin 3 with the voltmeter. If the voltage is now pulsating, the control head is internally shorted and should be replaced.
4. If the voltage on control head pin 3 is still a constant value, then the control head is OK. Check circuit 461, the serial data line, for an open or short to ground. If circuit 461 is OK, then the PROM and ECM must be investigated for faulty connections or internal malfunctions because it is not sending the Fuel Data information to the control head.
5. A pulsating voltage on the serial data line indicates that information is being transmitted by the ECM. A blank Fuel Data display can only be caused by a ECC control head which cannot interpret the data or by a Fuel Data display panel which cannot display the data. To isolate the cause of this condition, enter the diagnostic mode and note if the control head begins the diagnostic mode by displaying "-1.8.8". If "-1.8.8" is not displayed replace the control head. If "-1.8.8" appears, the ECC control head is OK because "-1.8.8" is the first word of the diagnostic message sent by the ECM. The Fuel Data panel should be replaced.

Performance Chart No. 11B - Improper Fuel Data Display. Scheme 157

The ECC control head is an integral part of the Fuel Data display system. The ECM determines fuel consumption based on vehicle speed and on the amount of fuel delivered to the engine. This information is sent to the ECC control head through the serial data line, circuit 461. The ECC control head interprets this information and illuminates the proper segments of the Fuel Data display panel.

1. To begin diagnosis, determine if the ECM is sending the proper information over the serial data circuit (circuit 441). If the "-1.8.8" segment check does not display upon entering diagnostics, the ECM may already be in the diagnostic mode. Refer to «CHART 12 - DIAGNOSTIC DISPLAY PROBLEMS»(/cadillac/fleetwood/75-series-1956-1992/remont/testing-diagnostics/#dfi-tests-wcodes) .
2. With .7.0 displayed, perform the "switch test" procedure to verify that the ECM can recognize the "instant/average" and "reset" buttons being depressed. If either code .7.8 or .7.9 do not pass, refer to the appropriate diagnostic procedure.
3. If any of the data panel's digits or segments fail to display or if the "instant" and "average" status lights do not illuminate properly, the control circuits must be checked using the information detailed in CHARTS 9, 10 and 11A.
4. If the "instant/average" and "reset" buttons work properly but the "fuel used" button does not turn on the "fuel used" status light after being depressed twice then the Fuel Data Panel is defective.
5. If the Data Panel continues to display "fuel used" after "range" as commanded on a vehicle with a mechanical speedometer, the ECM contains PROM for a digital cluster application. If the "fuel used" status light goes off after the "fuel used" button is depressed on a vehicle with digital cluster, the ECM contains PROM for a mechanical speedometer application. These conditions can be verified by displaying Engine Data Parameter .1.3 - PROM I.D.
6. If the display always reads "L" when "range" is commanded, the fuel signal is not being received by the ECM. If the fuel gauge is working properly, then circuit 30 must be open in either the wiring harness or in the ECM itself.

Performance Chart No. 12 - Diagnostic Display Problems. Scheme 158

1. Enter the diagnostic mode and note if ".." appears. The action of going from a temperature display to the beginning of the diagnostic routine ("..") is a function of the control head. If ".." does not appear, replace the control head.
2. If ".." remains displayed after entering diagnostics, the proper serial data information is not being received by the ECC control head. If the car starts, refer to «CHART 1 - NO START/STALL»(/cadillac/fleetwood/75-series-1956-1992/remont/testing-diagnostics/#dfi-tests-wcodes) .
3. If the "outside temperature" is displayed after entering diagnostics, the ECM is still sending fuel economy data over the serial data line. circuit 451 should be checked for an open since this circuit is used to signal the ECM to start sending diagnostic data.
4. If the "-1.8.S" is not displayed at the beginning of diagnostic display, the ECM may already be in the diagnostic mode. This would be the case if circuit 451 were shorted to ground.

Performance Chart No. 13 - Improper Idle Speed. Scheme 159

1. When improper idle speed is noted, the DFI system's self-diagnostic abilities should be utilized to evaluate the idle speed system. Enter diagnostics and investigate any stored codes.
2. The switch tests are also an important part of self-diagnostics which must all pass before further diagnosis.
3. Evaluate the idle speed when the engine coolant temperature (Parameter 04) reaches 85°C or greater. If a surging or rough idle is encountered, check for any of the following: A. Any problems in the EGR system which would prevent the EGR valve from closing completely during an idle and allow EGR gasses into the engine and upset the idle fuel requirements to the point where idle speed and quality is affected. Check to verify that close throttle is being reached. Perform the EGR system tests described in «CHART 7»(/cadillac/fleetwood/75-series-1956-1992/remont/testing-diagnostics/#dfi-tests-wcodes) . B. Low fuel pressure or improper injector operation will cause a rough idle condition by limiting the fuel delivery during the injector on-time. Refer to CHART 4 - FUEL SYSTEM DIAGNOSIS. C. Because of the additional load placed on the engine by the engagement of the A/C compressor clutch, the throttle angle must be raised whenever the clutch is actuated and reduced as the clutch is deactivated in order to maintain the programmed idle speed. The ECM senses compressor operation by monitoring the compressor signal circuit 977). To check this circuit, back probe Pin 21 of the P-2 (red) ECM connector with Voltmeter (part no. J-29125). Start the engine and set the ECC controls to Auto and 60°. The voltmeter should indicate a 12 volt signal which drops to 0 volts when the clutch engages. If the voltage does not drop sharply, the cycling switch could be bouncing and require replacement. D. Vacuum leaks in the intake system are compensated for by retracting the ISC plunger until the programmed "retract limits" are reached. Vacuum leaks can occur either in the intake manifold or engine and body vacuum circuits. E. Check for proper routing of the distributor wires away from the spark plug wires. Verify that the distributor wires are secured in place with the retainer clip. Keeping the proper distance between the distributor wires and the spark plug wires is important in order to eliminate mutual inductance: a condition where electrical signals enter the system from the outside, creating erratic operation. F. Check ignition timing. Open the set timing connector and check timing. Base (initial) timing should be 10° BTDC 800 RPM or less). If it isn't at 10°, reset the timing to 10°. Once it has been established that the base timing is correct, the system's ability to advance spark must be determined. With the set tinning connector reconnected, the spark timing should be between 20° and 30° BTDC at idle.
4. If the idle speed is too low (less than 500 RPM), then check for a low fuel pressure or improper injector operation. Insufficient fuel delivery could be causing of low idle speed. Refer to «CHART 4 - FUEL SYSTEM»(/cadillac/fleetwood/75-series-1956-1992/remont/testing-diagnostics/#dfi-tests-wcodes) .
5. If the idle speed is too high (more than 600 RPM), check any of the following: A. Check ignition timing. See step 3), part D. B. Check for misadjusted throttle position sensor and minimum air rate. If the self-diagnosis fails to reveal any malfunctions, the TPS adjustment should be checked. The actual value of the TPS signal is used by the ECM as an indicator of an actual throttle angle. C. Check for vacuum leaks in either the intake manifold or engine and body vacuum circuits.
6. With an improper idle speed, we must check the ISC actuator. The ISC operation can be checked using "output cycling." Verify that the plunger is able to extend and retract. If the ISC motor does not function properly, then treat the problem as a hard code 30. If the ISC motor is operating properly, then the problem is not in the DFI system.

Performance Chart No. 14 - Oxygen (O2) Sensor Test. Scheme 160

When the 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 oxygen sensor is warm (above 200°C), the output voltage will swing between O and 1.0 volts. When the ECM sees that the oxygen sensor is not at a cold voltage of 0.5 volt, it will send the system into closed loop operation. In closed loop operation, the ECM will meter fuel into the engine based on the oxygen sensor readings.

1. With the engine running warm (coolant temperature 85°C or greater) and at fast idle, observe engine data parameter .0.7. If there is no voltage variation and if the ECM and harness are operating properly, check for a faulty oxygen sensor connection or a faulty oxygen sensor. If the voltage remains between 30 and 60 for a minimum of one minute, check for the possibility of leaded or contaminated fuel (i.e., filler neck or catalytic converter has been tampered with) before checking for a faulty oxygen sensor connection or a faulty oxygen sensor.
2. While running the engine at a fast idle, observe the "open/closed loop" status light above the "off" button on the ECC control head. If the ECM switches the system to closed loop operation, then the oxygen sensor is OK If the ECM remains in open loop operation, then replace the oxygen sensor.

Performance Chart No. 15 - Improper Coolant Light Operation. Scheme 161

1. If the coolant light stays on with the engine coolant temperature below 120°C, it must be determined if the circuit is defective or if the ECM is turning the light on. If the light stays on with the ECM connector removed then circuit 35 is shorted to ground. If it goes off, the fault must be in the ECM connector or ECM.
2. The coolant light should come on when the ignition is first turned on (after a 10 second ignition off power-down). If it does not light, check the operation of the "Service Now" and Service Soon" lights during crank. If the "Service Now" and "Service Soon" lights work OK, the problem must be an open in circuit 35, the bulb or the ECM itself. If all three lights are inoperative, check the condition of the gauge fuse. If it is blown, check circuit 39 for a short to ground. If the gauge fuse is OK, measure the voltage at the gauge fuse with the ignition on. If the fuse has 12 volts on it, repair circuit 39 for an open. If voltage is not available at the fuse, the open circuit must be between the ignition switch and the fuse, repair as required.

Performance Chart No. 16 TCC Electrical Test. Scheme 162

The ECM completes the circuit for the TCC solenoid by grounding circuit 422. Grounding this circuit allows the solenoid to energize and supply oil pressure to the torque converter clutch.

1. To begin diagnosis connect a test light to circuit 422 on the ALDL diagnostic connect (pin F). With the TCC disengaged (ECM not grounding circuit 422) the test light should see 12 volts and light.
2. If the test light lights, then power is being supplied through the TCC brake switch. While in output cycling, circuit 422 should go between 12 volts and 0 volts every 3 seconds. If the test light does not flash, the transmission circuit should be checked for a shorted circuit. If the resistance between pins A and D is less than 15 ohms, the solenoid or the wires are shorted and should be repaired. This low resistance through the transmission may have damaged the ECM, therefore after repairs have been made check the output of the ECM in output cycling. If the resistance is greater than 15 ohms, then circuit 422 should be checked for an open to the ECM. If the wire is OK, check for a faulty ECM connector or faulty ECM.
3. If the test light does not light on circuit 422, then there must be an open between the ALDL connector and the battery. First check the TCC brake switch for proper operation. If there is no voltage on either side of the connector, then the switch or the circuit feeding the switch is open.
4. If there is voltage on both sides of the TCC brake switch, then the voltage on circuit 420 should be checked at the transmission. If the test light does not light, circuit 420 is open. If the test light lights between circuits 420 and 422 the circuit 422 is shorted to ground either in the harness or in the ECM itself.
5. If the test light between circuits 420 and 422 does not light when Pin F is jumpered to ground, circuit 422 is open. If it does light then an open or short must exist either in the transmission connector or in the transmission itself.

Trouble Codes

This is the code which is displayed in diagnostic display if the testing and failure requirements are both met. Codes 20, 23, 32, 33 and 39 have more than one set of requirements which will cause them to set. These different conditions are identified by a letter following the trouble code (i.e. 20-A and 20-B).

Testing Requirements

These are the conditions which must be met before the ECM will test for the failure requirements.

Failure Requirements

This is 1he input which the ECM identifies as abnormal under the conditions of the testing requirements. If a time is included in the requirements, this is how long all of the testing and failure requirements must be present in order to satisfy setting the trouble code.

Failsoft Action

After the ECM has identified a system malfunction, it may take some action to keep the vehicle operational. The following failsoft actions are taken by the ECM and are identified on the chart

1. N - No action taken
2. 1 - Coolant temp. set=MAT
3. 2 - Throttle angle set at 9°
4. 3 - HEI held in bypass spark
5. 4 - Brake on and TPS less than 11° = closed switch
6. 4 - Brake off or TPS more than 11° = open switch.
7. 5 - Code is kept hard for entire ignition cycle in which malfunction occurs and automatically stored as an intermittent upon starting of new ignition cycle
8. 6 - MAP is set at: 62 kPa if throttle is closed and RPM under 900 (62 - MPH)kPa if throttle is closed and RPM over 900 77% of BARO if throttle is open
9. 7 - BARO set at 93 kPa
10. 8 - MAT set = coolant temp
11. 5) Depending on the detected malfunction, certain functions will be disabled. These functions are disabled since their proper operation is dependent upon the input which has malfunctioned. The following functions are disabled and are identified on the chart
12. N - No Action Taken
13. A - Cruise Control
14. B - Air Management (de-energize both solenoids)
15. C - EGR (de-energize solenoid)
16. D - Canister Purge (de-energize solenoid)
17. E - TCC (de-energize solenoid)
18. F - Cruise Control disabled for entire ignition cycle in which malfunction occurred.
19. G - Closed Loop Control

ECM REPLACEMENT CHECK CHART

In order to reduce incidents of repeat ECM failure, a revised ECM diagnostic procedure is available. Beginning in 1982, most ECMs are equipped with Integrated Circuits (IC) in place of separate transistors to operate various controlled components.

These ICs, called Quad-Drivers (QDR), have 4 separate outputs, meaning that each QDR can operate up to 4 different components. An inoperative QDR can result in ECM output becoming open or shorted to ground. Often, all 4 outputs of a QDR will fail, even if just one QDR circuit is faulty.

Refer to the following tables to determine which ECMs contain QDRs. Since this procedure is not applicable to ECMs which do not contain QDRs, those ECMs are not listed.

Performing the diagnostic flow chart will identify an inoperative QDR. Once the circuit is identified, it must be repaired to eliminate repeat ECM failure. This diagnostic procedure must be used when "Replace ECM" is the conclusion of any procedure.

ECM QDR IDENTIFICATION

Scheme 163

Removal & Installation

Remove lower instrument panel cover. Remove 3 nuts securing ECM to instrument panel mounting brackets and ground strap. Remove 3 electrical connectors and remove ECM from vehicle. To install ECM, reverse removal procedure. Ensure ground strap is securely attached.

Removal

1. Remove ECM as previously described. Insert tip of small blade screwdriver into keyhole of locking tab on PROM access cover. Carefully bend tab slightly to unlock access cover and slide cover off ECM.
2. Note position of each PROM before removal. Replacement PROM's must be installed in same position as originals. Small reference boss (dimple) on PROM carrier must be aligned with boss dimple) on PROM socket. Grasp clear PROM between thumb and forefinger. Gently rock PROM back and forth while applying upward force to remove PROM and carrier. Repeat procedure to remove green PROM.

Note. PROMs are not interchangeable from generation to generation. Be sure part number of replacement PROM matches original PROM.

Scheme 164

1. Place PROM in clear carrier upside down on flat surface with pins facing up. Using a narrow blunt tool, press PROM body down on both sides of retainer bar so top of PROM is flush with top of carrier. Repeat procedure for PROM mounted in green carrier. (Scheme 164) (Scheme 164): Installing PROM into Electronic Control Module
2. Position clear PROM carrier squarely over PROM socket in ECM. Firmly press down on top of carrier. While holding carrier down, press body of PROM down with a blunt tool. Alternately pressing down on either end will securely seat PROM. Repeat procedure for PROM mounted in green carrier.
3. Install access cover on ECM and ensure it locks in place. Install ECM in vehicle. Start engine, enter diagnostics and check for code "51". If code "51" does not appear, PROM installation is correct. If code "51" is displayed, one or both PROMs are not fully seated, installed backwards, have bent pins or are defective.
4. If pins are bent, straighten pins and reinstall PROM. If pins break or crack during straightening process, replace BOTH PROMs. If PROMs are installed backwards, replace BOTH PROMs.

Remove center instrument panel applique. Remove 2 Fuel Data Display mounting screws and pull display out of instrument panel. Disconnect electrical connector. To install, reverse removal procedure.

THROTTLE POSITION SENSOR (TPS)

Note. DO NOT remove TPS unless all diagnosis confirms that TPS requires adjustment or repair.

1. Remove TPS electrical connector. Remove air cleaner and throttle body assembly. Turn throttle body upside down and support assembly to prevent damage to injector connectors. Using a 5/16" drill bit, drill completely through both TPS access holes in base of throttle body to remove spot welds holding screws in place.
2. Remove and discard TPS attaching screws. Remove lock washers and retainers. Remove TPS from throttle body, noting location of TPS pick-up lever in relation to throttle shaft lever tang for installation reference.

View of Throttle Body Assembly. Scheme 165

Installation

Position TPS over throttle shaft with TPS pick-up lever following throttle lever tang. Install retainers, lock washers and 2 new screws. Tighten screws so TPS will move but is not loose. Install throttle body, reconnect electrical connector and adjust TPS.

Disconnect harness connector from ISC. Remove 2 mounting screws and ISC. To install position ISC on left side of throttle body, install mounting screws and adjust ISC.

Remove instrument panel lower cover. Disconnect MAP vacuum hose and electrical connector. Remove screw securing MAP sensor to MAP/BARO bracket. Remove sensor. Reverse removal procedure to install.

Remove right side lower instrument panel and glove box liner. Disconnect harness connectors from both sensors and vacuum hose from MAP sensor. Remove screw holding ground strap to mounting bracket and remove mounting bracket screws. Remove sensors and bracket as an assembly. To install, reverse removal procedure.

Drain radiator until coolant level is below sensor. Remove alternator if required to gain access to sensor. Disconnect harness connector from sensor and remove sensor from block.

Apply non-hardening sealer to threads of sensor and install sensor. Reconnect harness connect and install alternator (if removed). Refill radiator.

Disconnect electrical connector and remove oxygen sensor. Install new oxygen sensor and ensure clearance is maintained at boot. When installing new sensor, do not remove coating from threads or install with any type of sealant. Reconnect electrical harness connector. (Scheme 166)

Note. DO NOT attempt to reinstall an oxygen sensor. Reinstallation of a sensor without the special glass bead thread coating may require replacement of exhaust system.

Oxygen Sensor Location. Scheme 166

DFI Control System Wiring Diagram. Scheme 167

See also:
• CHART 14 - O2 SENSOR TEST