Dfi BCM Tests W/codes Cadillac Eldorado IX

SELF-DIAGNOSTIC SYSTEM CHECK

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

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

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

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

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

Self-Diagnostic System Check Flow Chart. Scheme 1

Self-Diagnostic System Check Flow Chart. Scheme 2

CHART B1 - ODOMETER POWER/GROUND PROBLEM

An incorrect odometer reading can be caused by problems relating to power and ground circuits not only in Instrument Panel Cluster (IPC), but those of other components within the computer network, the computer wake-up signals, the vacuum fluorescent power supply, the odometer mileage memory chip (EEPROM) contained in BCM, or by data link between computer components.

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

1. If no codes are set in diagnostic memory, observe state of odometer reading with headlight switch and twilight sentinel switch in the "OFF" position. This is important because these signals can wake up the BCM and otherwise cause a misdiagnosis of a malfunctioning primary circuit.
2. When odometer reads all zeros, actuating the interior courtesy light switch will help to isolate exact cause of problem. This symptom is caused by a failure in system other than the IPC. Further isolation of this fault is diagnosed in CHARTS B2, B3 and B4.
3. When odometer is blank or reads all 8's, actuating headlight switch will help to isolate cause of problem. If odometer reads all zeros, cause of problem is due to a faulty "ISO IGN-3" feed circuit to BCM (open or shorted to ground) or BCM itself. If odometer is blank or reads all 8's, cause is due to one of several other problems within computer network.
4. Cycling the high beam or headlight dimmer switch will help to further isolate cause of problem. If high beams cycle, problem is related to IPC itself, IPC ground circuit, vacuum fluorescent power supply circuit or components related to these circuits. Further fault diagnosis is contained in CHART B5 - VACUUM FLUORESCENT POWER SUPPLY PROBLEM.
5. If high beams did not cycle when dimmer switch was actuated, turning on courtesy lights switch will help to further isolate system problem. If courtesy lights turn on, problem is related to IPC itself, the CPS-to-IPC logic circuits ground, the 12-volt power circuits from CPS to IPC, or the CPS itself. Further problem isolation is contained in CHART B6 - IPC-TO-CPS POWER/GROUND PROBLEM.
6. If courtesy lights did not turn on when switch was actuated, several other causes for problem can be isolated by following CHART B7 - BCM-TO-CPS WAKE-UP SIGNAL PROBLEM and CHART B8 - POWER LOSS FROM CPS TO OTHER COMPONENTS, depending on whether the lights on chime sounds when test is run.

Chart B1 Schematic, Odometer Power/Ground Problem. Scheme 3

Flow Chart B1, Odometer Power/Ground Problem. Scheme 4

Flow Chart B1, Odometer Power/Ground Problem. Scheme 5

CHART B2 - BCM-TO-IPC COMMUNICATION PROBLEM

You are at this chart because odometer, with key on, read all zeroes and courtesy lights turned on when switch was actuated. These symptoms indicate a loss of BCM data communication to the Instrument Panel Cluster (IPC), which is a result of one of several different possible problems.

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

1. If ALDL connector cover is off or loose, this could cause a break in data circuit, cutting off BCM communication to IPC under certain electrical conditions. Should this be the case, securely connect ALDL cover and return to beginning of SELF-DIAGNOSTIC SYSTEM CHECK.
2. Isolates ALDL connector, the ECM and programmer from data circuit in order to determine location of fault. If odometer reads actual accumulated miles, the fault lies within network between ALDL connector, the ECM and programmer.
3. Checks to see if fault is due to ECM and its related data circuits, or the programmer and its related circuits.
4. Determines if fault is associated with IPC or BCM.
5. Determines if fault is due to programmer, programmer's logic, or ground circuit No. 801 from Central Power Supply (CPS).

Chart B2 Schematic, BCM-To-IPC Communication Problem. Scheme 6

Flow Chart B2, BCM-To-IPC Communication Problem. Scheme 7

Flow Chart B2, BCM-To-IPC Communication Problem. Scheme 8

CHART B3 - CCDIC PROBLEM

You are at this chart because odometer problem has been isolated to CCDIC components or related data link circuitry.

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

1. This step restores circuit No. 800E into data link circuit. If odometer reads zero, the circuit is shorted to ground or voltage.
2. This step restores circuit No. 800C into data link circuit. If odometer continues to read correct mileage, the CCDIC must be replaced. If zeros return to the IPC, circuit No. 800C is at fault.

Flow Chart B3, CCDIC Problem. Scheme 9

Flow Chart B3, CCDIC Problem. Scheme 10

CHART B4 - BCM-TO-CPS POWER/GROUND PROBLEM

You are at this chart because odometer, with key on, read all zeroes and courtesy lights did not turn on when switch was actuated. These symptoms indicate that BCM has lost power or ground with Central Power Supply (CPS).

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

1. Checks for maximum blower speed with key on. Step will indicate whether BCM has lost logic ground circuit No. 801E with CPS.
2. This step determines if loss of logic ground is due to BCM, CPS or circuit No. 801E wire and terminals.
3. This step checks for 12 volts to BCM. If 12 volts is not present at BCM, fault is due to CPS or wiring.
4. Checks for 7 volts to BCM, which has 2 individual inputs fed from CPS. Loss of both signals would result in system fault, otherwise fault is due to a bad CPS or BCM.

Chart B4 Schematic, BCM-To-CPS Power/Ground Problem. Scheme 11

Flow Chart B4, BCM-To-CPS Power/Ground Problem. Scheme 12

Flow Chart B4, BCM-To-CPS Power/Ground Problem. Scheme 13

CHART B5 - VACUUM FLUORESCENT POWER SUPPLY PROBLEM

You are at this chart because odometer, with key on, read all 8's or was blank, but the high beams cycled when dimmer switch was activated. These symptoms indicate a problem with vacuum fluorescent power supply, located in IPC, display components, or related wiring.

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

1. Determines if fault is due to a bad CCDIC component.
2. Determines if fault is due to a bad radio component.
3. This step checks for ground integrity to Instrument Panel Cluster (IPC).
4. Determines if fault is due to a bad IPC or a short to ground in one of vacuum fluorescent power wires to CCDIC or radio.

Flow Chart B5, Vacuum Fluorescent Power Supply Problem. Scheme 14

Flow Chart B5, Vacuum Fluorescent Power Supply Problem. Scheme 15

Flow Chart B5, Vacuum Fluorescent Power Supply Problem. Scheme 16

CHART B6 - IPCTO-CPS POWER/GROUND PROBLEM

You are at this chart because odometer, with key on, read all 8's or was blank, the high beams would not cycle, but courtesy light came on when switch was activated. These symptoms indicate Instrument Panel Cluster (IPC) has lost 12 volts power or ground with Central Power Supply (CPS).

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

1. Checking CCDIC display indicates whether IPC has ground.
2. Disconnecting the IPC and checking resistance in circuit No. 801A determines if fault is due to the IPC, wiring and terminals, or the CPS.
3. This step checks if 12 volts is available from the CPS. If not, fault is due to wiring or CPS.
4. With 12 volts available from CPS, this step checks if fault is due to IPC or flex circuit between transition block and IPC.

Flow Chart B6, IPCTO-CPS Power/Ground Problem. Scheme 17

Flow Chart B6, IPCTO-CPS Power/Ground Problem. Scheme 18

Flow Chart B6, IPCTO-CPS Power/Ground Problem. Scheme 19

CHART B7 - BCM-TO-CPS WAKE-UP SIGNAL PROBLEM

You are at this chart because odometer, with key on, read all 8's, was blank, high beams would not cycle, courtesy lights would not turn on, but lights on chime would sound when activated. These symptoms indicate a loss of 7 volts from Central Power Supply (CPS) to data network components, used to power the microprocessor chip. Or, the CPS has lost system wake-up signal from BCM, which is used to turn on 7 volt power supply.

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

1. This step checks circuit No. 555, CPS wake-up signal, for a short to ground, a fault in BCM or BCM connector, or a bad CPS.
2. This step checks for an open in circuit No. 555.
3. This step checks for an open circuit in CPS ground, which will disable 7-volt power supply.
4. This step checks for short to ground in each 7-volt circuit from CPS, for a faulty component in network, or a faulty CPS.

Chart B7 Schematic, BCM-To-CPS Wake-Up Signal Problem. Scheme 20

Flow Chart B7, BCM-To-CPS Wake-Up Signal Problem. Scheme 21

Flow Chart B7, BCM-To-CPS Wake-Up Signal Problem. Scheme 22

CHART B8 - POWER LOSS FROM CPS TO OTHER COMPONENTS

You are at this chart because odometer, with key on, read all 8's, was blank, high beams would not cycle, courtesy lights would not turn on, or light on chime would not sound when test was attempted. These symptoms indicate a loss of 12 volts from Central Power Supply (CPS) to other components in system.

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

1. This step checks whether battery voltage is feeding CPS.
2. This step checks for an open in circuit No. 640, CPS battery feed, poor terminal contact, or a faulty CPS.
3. This step checks for an intermittent short to ground condition on any of 12-volt circuits from CPS or in circuit No. 640 feed.
4. This step checks for a short to ground in circuit No. 640.
5. This step checks each individual 12-volt circuit from CPS for a short to ground, a faulty component, or a faulty CPS.

Chart B8 Schematic, Power Loss From CPS To Other Components. Scheme 23

Flow Chart B8, Power Loss From CPS To Other Components. Scheme 24

Flow Chart B8, Power Loss From CPS To Other Components. Scheme 25

CHART C1 - CCDIC SYMPTOM DIAGNOSIS

This chart should be used to identify symptoms relating to CCDIC problems. There are 2 major checks that must be made, a visual check of the display, and a keyboard functional check.

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

1. If the CCDIC display is totally blank, go to CHART C2 - CCDIC COMPLETELY BLANK. If Climate Control Panel (CCP) is blank, but Driver Information Center (DIC) reads "SYSTEM PROBLEM", go to CHART C3 - CCDIC DISPLAY READS "SYSTEM PROBLEM". Any other display problems are due to the CCDIC and it should be replaced.
2. If the "TEMP/TIME" button is the only inoperative button, go to CHART C4 - CCDIC DISPLAY READS "SYSTEM PROBLEM". Cause of problem may be an open in circuit No. 1018. If none of the buttons on the engine panel respond, the CCDIC panel or BCM should be replaced.
3. If the DIC buttons do not respond, check BCM input B130. This checks to see if the BCM and related wiring are at fault, or the CCDIC panel.
4. This step checks to see if there is a short to ground in circuit No. 1018, a faulty BCM, or a faulty CCDIC panel.

Chart C1 Schematic, CCDIC Symptom Diagnosis. Scheme 26

Flow Chart C1, CCDIC Symptom Diagnosis. Scheme 27

Flow Chart C1, CCDIC Symptom Diagnosis. Scheme 28

CHART C2 - CCDIC COMPLETELY BLANK

You are at this chart because the CCDIC display is completely blank. Cause for this problem could be a loss of Central Power Supply (CPS) power or ground, or loss of vacuum fluorescent power from Instrument Panel Cluster (IPC).

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

1. Unplugging the CCDIC connector and performing individual circuit checks will determine if wiring connector, terminals, or component is faulty.

Chart C2 Schematic, CCDIC Completely Blank. Scheme 29

Flow Chart C2, CCDIC Completely Blank. Scheme 30

Flow Chart C2, CCDIC Completely Blank. Scheme 31

CHART C3 - CCDIC DISPLAY READS "SYSTEM PROBLEM"

You are at this chart because the Driver Information Center (DIC) display reads "SYSTEM PROBLEM". This symptom is the result of a data link problem.

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

1. Checks to see if data link is faulty or the CCDIC panel.
2. This step checks to see where problem exists in data link, including the CCDIC panel.

Flow Chart C3, CCDIC Display Reads "SYSTEM PROBLEM". Scheme 32

Flow Chart C3, CCDIC Display Reads "SYSTEM PROBLEM". Scheme 33

CHART C4 - CCDIC "TIME/TEMP" BUTTON DOESN'T RESPOND

You are at this chart because the "TIME/TEMP" button does not respond on Driver Information Center (DIC) panel.

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

1. This step determines if fault is due to loss of 12 volts to CCDIC panel from CPS, including components, or an open in circuit No. 1018 from CCDIC panel to the BCM, including components.

Flow Chart C4, CCDIC "TIME/TEMP" Button Doesn't Respond. Scheme 34

Flow Chart C4, CCDIC "TIME/TEMP" Button Doesn't Respond. Scheme 35

BCM TROUBLE CODE IDENTIFICATION

BCM TROUBLE CODE IDENTIFICATION

BCM CODE B110 - OUTSIDE AIR TEMPERATURE SENSOR CKT

The outside air temperature sensor uses a thermistor to control signal voltage to BCM. The BCM supplies voltage on circuit No. 735 to sensor. When sensor is cold, its resistance is high, therefore BCM will see a high signal voltage. As sensor warms, its resistance becomes less and signal voltage is pulled low through sensor ground, circuit No. 736. This signal voltage will vary between 5 volts (open circuit) and zero volts (shorted circuit).

Code B110 will set if signal voltage indicates less than -34°C (open circuit) or more than 87°C (shorted circuit). During a failure, a substitute temperature reading will be used to allow continued operation of A/C-heater system and compressor will not run continuously at idle.

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

1. BCM data code BD26 will display actual sensor reading. The normal range is from -34°C to 87°C.
2. Checks to see if open circuit reading is due to circuit or sensor. If open circuit reading changes to a shorted circuit reading after jumping sensor terminals, BCM and wiring are okay.
3. By applying a ground to various points in circuits, an open can be isolated by observing whether parameter display can be changed from open reading to shorted reading.
4. Checks if shorted circuit reading is caused by circuit or sensor. If shorted circuit reading changes to an open circuit reading after disconnecting sensor, BCM and wiring are okay.

NOTES ON INTERMITTENTS

A code B110 will be stored in memory whenever the ambient temperature drops below -29°F (-34°C). This code should be ignored if this cause is suspected.

If intermittent code B110 is being set, manipulate related wiring while observing BCM data code BD26. If failure is induced, reading will jump from its normal value to a reading outside range of -34°C to 87°C.

If value displayed by BD26 is not reasonably close to actual temperature of air at sensor, check for poor terminal connections or replace sensor.

Code B110 Schematic, Outside Air Temp. Sensor Circuit. Scheme 36

Code B110 Flow Chart, Outside Air Temp. Sensor Circuit. Scheme 37

Code B110 Flow Chart, Outside Air Temp. Sensor Circuit. Scheme 38

BCM CODE B111 - A/C HIGH SIDE TEMPERATURE SENSOR CKT

The A/C high side temperature sensor is a thermistor that controls signal voltage to BCM. The BCM supplies voltage on circuit No. 732 to sensor. When sensor is cold, its resistance is high, therefore BCM will see a high signal voltage. As sensor warms, its resistance becomes less and signal voltage is pulled low through sensor ground, circuit No. 736. This signal voltage will vary between 5 volts (open circuit) and zero volts (shorted circuit).

Code B111 will set if ignition is on, outside air temperature sensor is functioning properly and reading above 0°C, and signal voltage indicates less than -34°C (open circuit) or more than 209°C (shorted circuit). During a failure, a substitute temperature reading is used to allow continued operation of A/C-heater system and A/C high side temperature reading BD27 will display actual sensor reading.

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

1. BCM data code BD27 displays A/C high side temperature. Normal range is from -34°C to 209°C.
2. Checks to see if open circuit reading is due to circuit or sensor. If open circuit reading changes to shorted circuit reading after jumping sensor terminals, BCM and wiring are okay.
3. By applying ground to various points in circuits, an open can be isolated by observing whether parameter display can be changed from open reading to shorted reading.
4. Checks if shorted circuit reading is caused by circuit or sensor. If shorted circuit reading changes to an open circuit reading after disconnecting the sensor, BCM and wiring are okay.

If intermittent code B111 is being set, manipulate related wiring while observing BCM data code BD27. If failure is induced, reading will jump from its normal value to a reading outside range of -34°C to 209°C. If value of sensor displayed by BD27 is not reasonably close to pressure gauge reading, check for poor terminal connections or replace sensor.

Code B111 Flow Chart, A/C High Side Temp. Sensor Circuit. Scheme 39

Code B111 Flow Chart, A/C High Side Temp. Sensor Circuit. Scheme 40

BCM CODE B112 - A/C LOW SIDE TEMPERATURE SENSOR CKT

The A/C low side temperature sensor is a thermistor that controls signal voltage to BCM. The BCM supplies voltage on circuit No. 731 to sensor. When sensor is cold, its resistance is high, therefore BCM will see a high signal voltage. As sensor warms, its resistance becomes less and signal voltage is pulled low through sensor ground, circuit No. 736. This signal voltage will vary between 5 volts (open circuit) and zero volts (shorted circuit).

Code B112 will set if signal voltage indicates less than -34°C (open circuit) or more than 87°C (shorted circuit). During a failure, a substitute temperature reading (ambient temperature reading) is used to allow continued operation of climate control system. The A/C compressor clutch will also be disabled and A/C low side temperature reading BD28 will display actual sensor reading.

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

1. BCM data code BD28 displays A/C low side temperature. Normal range is from -34°C to 87°C.
2. Checks if open circuit reading is caused by circuit or sensor. If open circuit reading changes to shorted circuit reading after disconnecting sensor, BCM and wiring are okay.
3. By applying ground to various points in circuits, an open can be isolated by seeing if parameter display can be changed from open reading to shorted reading.
4. Checks to see if shorted circuit reading is caused by circuit or sensor. If shorted circuit reading changes to an open circuit reading after disconnecting sensor, BCM and wiring are okay.

If intermittent code B112 is being set, manipulate related wiring while observing BCM data code BD28. If failure is induced, reading will jump from its normal value to a reading outside range of -34°C to 87°C.

If value displayed by data parameter BD28 is not reasonably close to corresponding pressure gauge reading, check for poor terminal connections or replace sensor.

Code B112 Flow Chart, A/C Low Side Temp. Sensor Circuit. Scheme 41

Code B112 Flow Chart, A/C Low Side Temp. Sensor Circuit. Scheme 42

BCM CODE B113 - IN-CAR TEMPERATURE SENSOR CIRCUIT

The in-car air temperature sensor is a thermistor that controls signal voltage to BCM. The BCM supplies voltage on circuit No. 734 to sensor. When sensor is cold, its resistance is high, therefore BCM will see a high signal voltage. As sensor warms, its resistance becomes less and signal voltage is pulled low through sensor ground, circuit No. 736. This signal voltage will vary between 5 volts (open circuit) and zero volts (shorted circuit).

Code B113 will set if ignition is on, outside temperature sensor is working properly, ambient temperature is above -18°C and signal voltage indicates less than -34°C (open circuit) or more than 96°C (shorted circuit). During a failure, a substitute temperature reading is used to allow continued operation of A/C-heater system and in-car temperature reading BD25 will display actual sensor reading.

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

1. BCM data code BD25 displays in-car temperature. Normal range is -34°C to 96°C.
2. Checks if open circuit is caused by circuit or sensor. If open circuit reading changes to shorted circuit reading after disconnecting sensor, BCM and wiring are okay.
3. By applying ground to various points in circuits, an open can be isolated by observing whether parameter display can be changed from open reading to shorted reading.
4. Checks to see if shorted circuit reading is caused by circuit or sensor. If short circuit reading changes to an open circuit reading after disconnecting sensor, BCM and wiring are okay.

If intermittent code B113 is being set, manipulate related wiring while observing BCM data code BD25. If failure is induced, reading will jump from its normal value to a reading outside range of -34°C to 96°C.

If value displayed by BD25 is not reasonably close to actual temperature of air at sensor, check for poor terminal connections or replace sensor.

Code B113 Flow Chart, In-Car Temperature Sensor Circuit. Scheme 43

Code B113 Flow Chart, In-Car Temperature Sensor Circuit. Scheme 44

BCM CODE B115 - SUNLOAD TEMPERATURE SENSOR

The sunload sensor uses a thermistor to control signal voltage to BCM. The BCM supplies voltage on circuit No. 590 to sensor. When sensor is cold, resistance is high, therefore BCM will see high signal voltage. As sensor warms, resistance is lowered, signal voltage is pulled low through circuit No. 736 to ground. Signal voltage will vary between 5 volts (open circuit) and zero volts (shorted circuit).

Code B115 will set when ignition is on, outside temperature sensor is working properly, ambient temperature is more than -18°C and signal voltage indicates less than -34°C (open circuit) or more than 96°C (shorted circuit). During a failure, a substitute temperature reading is used to allow continued operation of A/C-heater system and sunload temperature reading BD32 will display actual sensor reading.

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

1. BCM data code BD32 displays sunload temperature. Normal range is -34°C to 96°C.
2. Checks if open circuit is caused by circuit or sensor. If open circuit reading changes to shorted circuit reading after jumping sensor terminals, BCM and wiring are okay.
3. By applying ground to various points in circuits, an open can be isolated by observing whether parameter display can be changed from open reading to shorted reading.
4. Checks if short circuit reading is caused by circuit or sensor. If short circuit reading changes to an open circuit reading after disconnecting sensor, BCM and wiring are okay.

If intermittent code B115 is being set, manipulate related wiring while observing BCM data code BD32. If failure is induced, reading will jump from its normal value to a reading outside range of -34°C to 96°C. If value displayed by BD32 is not reasonably close to actual thermometer reading, check for poor terminal connections or replace sensor.

Code B115 Flow Chart, Sunload Temperature Sensor. Scheme 45

Code B115 Flow Chart, Sunload Temperature Sensor. Scheme 46

BCM CODE B119 - TWILIGHT PHOTOCELL CIRCUIT

Note. Ensure sensor is not obstructed before following procedure.

The twilight sensor uses a photocell to control signal voltage to BCM. The BCM supplies voltage on circuit No. 278 to sensor. When sensor detects darkness, resistance is high, therefore BCM will see high signal voltage. As sensor detects light, resistance is lowered, signal voltage is pulled low through circuit No. 736 to ground. Signal voltage will vary between 5 volts (open circuit) and zero volts (shorted circuit).

Code B119 will set when ignition is on, signal voltage indicates more than 94 percent (open circuit) or less than 6 percent (shorted circuit). During a failure, a substitute light reading (indicating darkness) will be used to allow continued operation of headlights and light reading BD44 will display actual sensor reading.

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

1. BCM data code BD44 displays light level. Normal range is 6-94 percent.
2. Checks if open circuit is caused by circuit or sensor. If open circuit reading changes to shorted circuit reading after jumping sensor terminals, BCM and wiring are okay.
3. By applying ground to various points in circuits, an open can be isolated by observing whether parameter display can be changed from open reading to shorted reading.
4. Checks if short circuit reading is caused by circuit or sensor. If short circuit reading changes to an open circuit reading after disconnecting sensor, BCM and wiring are okay.

If intermittent code B119 is being set, manipulate related wiring while observing BCM data code BD44. If failure is induced, reading will jump from its normal value to a reading outside the range of 6-94 percent. Ensure owner is advised not to cover sensor.

Code B119 Schematic, Twilight Photocell Circuit. Scheme 47

Code B119 Flow Chart, Twilight Photocell Circuit. Scheme 48

Code B119 Flow Chart, Twilight Photocell Circuit. Scheme 49

BCM CODE B120 - TWILIGHT DELAY POT CIRCUIT

The twilight delay uses a potentiometer to control signal voltage to BCM. The BCM supplies voltage on circuit No. 705 to resistor in left switch assembly and grounds through circuit No. 736 to BCM. The wiper supplies voltage signal to BCM on circuit No. 271 indicating position of slider and delay time. When slider is moved toward maximum position, resistance is low, therefore BCM will see high signal voltage. When slider is moved toward minimum position, resistance increases and signal voltage decreases. Signal voltage varies between zero volts (open or grounded circuit) and 5 volts (shorted voltage).

Code B120 will set when ignition is on, signal voltage indicates less than 6 percent (open or grounded circuit) or more than 94 percent (shorted to voltage). During a failure, a substitute delay time (minimum delay) is used to allow continued operation of twilight system and reading from BD43 will display actual reading.

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

1. BCM data code BD43 displays twilight delay. Normal range is between 6-94 percent.
2. Checks if open circuit is caused by circuit or switch assembly. If open or grounded circuit reading changes to a short to voltage reading after jumping switch assembly terminals, BCM and wiring are okay.
3. Measuring voltage between circuit No. 705 (5 volts) and circuit No. 271 will determine if circuit No. 271 is open or shorted to ground.
4. Checks if short to voltage circuit reading is caused by circuit or switch assembly. If a short to voltage reading changes to an open circuit reading after disconnecting switch assembly, BCM and wiring are okay.

If intermittent code B120 is being set, manipulate related wiring while observing BCM data code BD43. If failure is induced, reading will jump from its normal value to a reading outside the range of 6-94 percent

Code B120 Flow Chart, Twilight Delay Pot Circuit. Scheme 50

Code B120 Flow Chart, Twilight Delay Pot Circuit. Scheme 51

BCM CODES B120 & B122 - TWILIGHT DELAY & PANEL DIMMING

Since both potentiometers use the same power and ground circuits, chance of problem being in power or ground circuit is very good when both codes are stored.

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

1. BCM data code BD43 displays a twilight delay value. Normal range is between 6-94 percent.
2. Checks if open circuit is caused by circuit or switch assembly. If voltage can be read across circuit Nos. 705 & 736 after disconnecting switch assembly, BCM and wiring are okay.
3. Check for 5-volt reference signal at switch. If 5 volts is read, circuit No. 736 is open. If circuit No. 736 is open, the open is between terminal "BC10" on left switch assembly and cavity "C3" on dash/instrument panel transition connector.
4. If circuit No. 705 is suspected of being grounded, remove A/C-heater programmer and BCM connectors before making a ground check.
5. If there is no ground on circuit No. 705, replace the A/C-heater programmer or BCM.

If intermittent codes B120 and B122 are being set, manipulate related wiring while observing BCM data codes BD42 and/or BD43. If failure is induced, reading will jump from its normal value to a reading outside of 6-94 percent.

Codes B120 & B122, Twilight Delay & Panel Dimming. Scheme 52

BCM CODE B121 - TWILIGHT ENABLE SWITCH

The twilight enable switch uses a physical control as the delay potentiometer. Inside left switch assembly, the enable switch contacts close when the time delay slider is moved to "OFF" position. The Instrument Panel Cluster (IPC) supplies voltage on circuit No. 304 to switch. When slider is moved from "OFF" position, the switch contacts close and signal voltage is pulled low through circuit No. 736 to ground.

Code B121 will set when ignition is on, twilight delay potentiometer is working properly (code B120) and signal voltage is high when the delay slider is moved from "OFF" position (open circuit), or signal voltage is low when the delay slider is in "OFF" position (shorted circuit).

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

1. IPC input value II82 displays voltage state of circuit No. 304 at IPC. These conditions can be observed in IPC input display as readings of high or low when delay slider is moved.
2. Checks if "LO" reading is caused by circuit or switch assembly. If display changes from "LO" to "HI" when the switch assembly is disconnected, IPC is okay.
3. Checks if "HI" reading is caused by circuit or switch assembly. If display changes from "HI" to "LO" when switch terminals are jumped together, the IPC and wiring are okay.

When IPC II82 input change-of-state indicator displays an "X", check circuit for an intermittent open. Cycle twilight control between "OFF" and "MAX" delay. If BCM data code BD43 does not read between 6-94 percent, replace left switch assembly.

Code B121 Flow Chart, Twilight Enable Switch. Scheme 53

Code B121 Flow Chart, Twilight Enable Switch. Scheme 54

BCM CODE B122 - PANEL LIGHT DIMMING POT CIRCUIT

The panel dimmer uses a potentiometer to control signal voltage to BCM. The BCM supplies voltage on circuit No. 705 to resistor in left switch assembly and returns to BCM on circuit No. 736 as ground. Wiper provides voltage signal to BCM on circuit No. 686 indicating position of thumbwheel and dim level. When thumbwheel is moved toward maximum (bright), resistance is low, therefore BCM will see a high signal voltage. When thumbwheel is moved toward minimum (dim), resistance is higher and signal voltage to BCM becomes less.

Code B122 will set when ignition is on and signal voltage indicates less than 6 percent (open or grounded circuit) or more than 94 percent (shorted to voltage). During failure, a substitute dimming value is used to allow continued operation of interior lighting and potentiometer reading BD42 will display actual sensor reading.

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

1. BCM data code BD42 displays amount of panel dimming. Normal range is between 6-94 percent.
2. Checks if open is caused by circuit or switch assembly. If open or grounded circuit reading changes to a shorted to voltage reading after jumping switch terminals, BCM and wiring are okay.
3. Measuring voltage between circuit No. 705 (5 volts) and circuit No. 686 will determine if circuit No. 686 is open or shorted to ground.
4. Checks if short to voltage reading is caused by circuit or switch assembly. If short to voltage reading changes to an open circuit reading after disconnecting switch assembly, BCM and wiring are okay.

If intermittent code B122 is being set, manipulate related wiring while observing BCM data code BD42. If failure is induced, reading will jump from its normal value to a reading outside range of 6-94 percent.

Code B122 Flow Chart, Panel Light Dimming Pot Circuit. Scheme 55

Code B122 Flow Chart, Panel Light Dimming Pot Circuit. Scheme 56

BCM CODE B123 - COURTESY LIGHT SWITCH

The courtesy lights panel switch is part of the dimmer control potentiometer. In left switch assembly the "COURTESY LIGHTS ENABLE" switch closes when dimmer is moved to extreme right. The BCM supplies signal voltage on circuit No. 685 which is pulled to ground through circuit No. 736 when switch contact is closed.

Code B123 will set when ignition is on, dimming potentiometer is working properly (code B122) and signal voltage is high when dimmer is moved to enable position or signal voltage is low when dimmer is moved to maximum dim position.

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

1. BCM input value B101 displays the voltage state of circuit No. 685 at BCM.
2. Checks if open circuit reading (HI) is caused by circuit or switch assembly. If display changes from "HI" to "LO" when switch terminals are jumped together, BCM and wiring are okay.
3. Checks if open circuit reading is caused by BCM or wiring.
4. With courtesy lights switch off, checks if short to ground reading is due to switch assembly or wiring.

If intermittent code B123 is being set, manipulate circuit No. 685. When BCM input B101 change-of-state indicator displays an "X", check circuit at that location for intermittent fault.

Code B123 Flow Chart, Courtesy Light Switch. Scheme 57

Code B123 Flow Chart, Courtesy Light Switch. Scheme 58

BCM CODE B124 - VEHICLE SPEED SENSOR CIRCUIT

The vehicle speed sensor (VSS) uses a permanent magnet generator to produce an electrical signal representative of vehicle speed. This signal is sent to the BCM by circuit No. 400 (VSS HI) and circuit No. 401 (VSS LO) where the BCM buffers and amplifies the signal for its different uses. Output of the generator can be seen by using a digital voltmeter (A/C scale) while rotating the generator drive (rotating front wheels).

Code B124 will set when ignition is on, no code B334 or EO28, no input to BCM from VSS, transaxle in 4th gear (°F status light), and engine speed greater than 1300 RPM. During a failure, the compressor at idle will be disabled and vehicle speed reading BD60 will display actual sensor reading.

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

1. Since the BCM amplifies and buffers the speed signal before its sent to the ECM, code E024 in ECM will be set along with code B124 in the BCM if permanent magnet generator or circuit Nos. 400 and 401 have a problem. If there is a problem with the vehicle speed sensor circuit, and no code EO24 is set, there is an internal problem with the BCM.
2. BCM data code BD60 displays MPH.
3. With front wheels turning, a voltage reading indicates that permanent magnet generator and wiring are okay.
4. Checks for an open in VSS circuit wiring.
5. Checks ground in VSS circuit wiring prior to replacing sensor.

If intermittent code B124 is being set, manipulate related wiring while observing BCM data code BD60. If a failure is induced, reading will jump from normal value to zero MPH.

Code B124 Schematic, Vehicle Speed Sensor Circuit. Scheme 59

Code B124 Flow Chart, Vehicle Speed Sensor Circuit. Scheme 60

Code B124 Flow Chart, Vehicle Speed Sensor Circuit. Scheme 61

BCM CODE B127 - PRND321 SENSOR

The PRND321 switch is a multi-signal switch sending information relative to gear selector position to BCM and ECM. Switch is mounted on transaxle assembly. The switch assembly also contains neutral safety switch, back-up light switch, and provides park input to automatic door lock module (if equipped). The switch uses 4 discrete circuits to pull BCM terminal voltages low in various combinations to indicate each gear selection. Voltage level of each circuit is represented in BCM data code BD41 as "0" for low, "1" for high. The 4 digits displayed represent decoder "A", "B", "C" and "PARITY" inputs in sequence.

The PRND321 switch also provides park/neutral input to the ECM in a similar manner using one discrete input. This is seen using the ECM input EI74 where "HI" or "LO" represent voltage level of the input terminal.

Code B127 sets when BCM PRND321 input indicates park/neutral but ECM input does not, BCM PRND321 input does not indicate park/neutral but ECM input does, or decoder and parity inputs do not agree with possible combinations of "CORRECT VALUES" chart. If code B127 is set, CCDIC will display the "GEAR SELECT PROBLEM" warning and Instrument Panel Cluster (IPC) will flash "PRND321" display.

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

1. 1) Checks BCM inputs when only decoder "A" and "PARITY" circuit are pulled low.
2. 2) Checks BCM inputs only when decoder "B" and "C" inputs are pulled low. This will complete voltage check of all 4 BCM inputs.
3. 3) Checks for a PRND321 switch problem in other gear ranges.
4. 4) Checks if code is due to discrepancy between ECM and BCM inputs.

Manipulate related BCM and ECM wiring in each gear range while observing BD41 or EI74 values. If a failure is induced, values will change indicating an open or short to ground. Ensure good terminal connections exist at BCM, ECM and PRND321 switch. If terminal contacts are good and code B127 continues to set, replace BCM.

Code B127 Schematic, PRND321 Sensor (1 Of 2). Scheme 62

Code B127 Flow Chart, PRND321 Sensor (1 Of 2). Scheme 63

Note. Do not attempt to diagnose this code unless owner complaint is of "Gear Selector Fault" message on the DIC, a "Boxed" PRND321 display on the IPC, or improper gear selection display.

Code B127 Flow Chart, PRND321 Sensor. Scheme 64

1. 5) Checks for short to ground in PRND321 to BCM circuit(s).
2. 6) Checks for open in PRND321 to BCM circuit(s).
3. 7) Circuit shorted to ground will result in a "0" display for the circuit.
4. 8) Checks for open PRND321 sensor ground.
5. 9) Open circuit will result in a "1" display for the circuit.

Code B127 Flow Chart, PRND321 Sensor (2 Of 2). Scheme 65

Code B127 Flow Chart, PRND321 Sensor (1 Of 2). Scheme 66

BCM CODE B334 - LOSS OF ECM DATA

If BCM cannot exchange data with ECM and ignition is on, code B334 will be set. If other communication codes are stored along with code B334, see MULTIPLE INTERMITTENT CODES option in this article. If code B334 is the only code stored, failure will be located as an open in circuit No. 800H, or an open in circuit Nos. 800J and 800G, or a faulty ECM or ECM MEM-CAL.

During a failure a fail soft value equal to 100°C will be used for coolant temperature. The cooling fans will be ran at high speed and no ECM diagnostic information will be available for display. While in the service diagnostic mode, this code will remain active, always checking for proper operation.

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

1. Checks for intermittent operating conditions.
2. Checks if open is in circuit No. 800H or rest of data circuitry.
3. A double open condition is isolated in this step. Condition occurs on both sides of ECM, in dash side of data line.
4. Isolates fault to be a poor terminal contact at engine dash harness interconnect circuit No. 800H or ECM.

If only code B334 is stored as a history code, check power and grounds for an intermittent open in circuit Nos. 800J and 800G. If ECM code EO52 is also set as a history code, see ECM CODE EO52 - ECM MEMORY RESET chart in the DFI ECM TESTS/CODES article in this section.

Code B334 Flow Chart, Loss Of ECM Data. Scheme 67

Code B334 Flow Chart, Loss Of ECM Data. Scheme 68

HISTORY CODES EO47, B334, B335, B336 & B337

This combination of codes could be caused by any of the following conditions

1. Momentary short to ground or voltage anywhere in data circuit No. 800 or in any microprocessor based components (i.e., BCM, ECM, CCDIC, or A/C-heater programmer).
2. Loose ECM MEM-CAL.
3. Momentary opens in data circuit isolating BCM from communication with all other components in the network.
4. Momentary open in CCDIC ground circuit No. 801B.
5. Momentary open in IPC ground circuit No. 801A.

HISTORY CODES EO47 & B334

This combination of codes could be caused by any of the following conditions

1. Momentary open in ECM data circuit No. 800E or faulty ECM.
2. Momentary opens in data circuit isolating ECM from communication with BCM. The opens would be in circuit Nos. 800E and 800F, 800G, 800H, ALDL cover or BCM.

HISTORY CODES EO47 & B337

This combination of codes could be caused by any of the following conditions

1. Momentary open in BCM power circuit No. 812C from CPS.
2. Momentary opens in BCM ground circuit Nos. 801C and 801E.

HISTORY CODES EO47, B334 & B337

This combination of codes could be caused by any of the following conditions

1. Momentary open in data circuit isolating BCM from communication with ECM and programmer. One open would be in circuit No. 800C, the other in circuit Nos. 800F, 800G, ALDL cover or components.

HISTORY CODES EO47, B334, B335 & B337

This combination of codes could be caused by any of the following conditions

1. Momentary opens in data circuit isolating BCM from communication with ECM, programmer and CCDIC. One open would be in circuit No. 800B, the other would be in circuit Nos. 800F, 800G, ALDL cover or components.

HISTORY CODES B335, B336 & B337

This combination of codes could be caused by any of the following conditions

1. Momentary opens in data circuit isolating BCM from communication with CCDIC, IPC and programmer. One open would be in circuit No. 800E, other open in circuit No. 800A, including components.

HISTORY CODES B355 & B336

This combination of codes could be caused by any of the following conditions

1. Momentary opens in data circuit isolating BCM from communication with CCDIC and IPC. One open would be in circuit No. 800A, the other in circuit No. 800C, including components.

HISTORY CODES B335 & B337

This combination of codes could be caused by any of the following conditions

1. Momentary opens in data circuit isolating BCM from communication with CCDIC and programmer. One open would be in data circuit No. 800B, the other in circuit No. 800D, including components.

BCM CODE B335 - LOSS OF CCDIC DATA

Since a loss of data communication with CCDIC will result in "SYSTEM PROBLEM" display, this code can only be recognized as a history code. During a failure, the A/C-heater programmer will default to 75°F set temperature, front defrost air delivery and automatic blower control.

With a 2-way, redundant communication ability built into this system, a double open in data line must occur to set fault. A single fault, however, in the CCDIC power or ground would also cause this code to set.

BCM Code 335 indicates a loss of data communication between the CCDIC and the BCM. When this event occurs, the CCDIC displays the message "SYSTEM PROBLEM" until the problem is corrected. This code will only be displayed as an intermittent.

Possible cause of a code 335 are

1. A faulty CCDIC panel.
2. Loss of 7 volts from the central power supply (circuit 807).
3. The actual loss of the data communication circuit to the BCM.

BCM CODE B336 - LOSS OF IPC DATA

If BCM loses data communication with IPC and ignition is on, code B336 will be set. The problem is a result of 7-volt or ground fault to IPC or double open circuit in data communication line between IPC and BCM. If this failure occurs, cruise control will disengage (if engaged) and headlights (if on) will function on low beam.

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

1. Checks for an intermittent condition.
2. Checks if problem is related to power and ground circuits or data communication line.
3. Determines if data problem is due to IPC or wiring.
4. Determines if fault is due to an open in circuit Nos. 800E and 800C or an internal IPC problem.
5. Checks if fault is due to 7-volt power circuit or ground circuit from CPS.
6. Checks ground circuit for an open condition, faulty IPC or a faulty CPS.

If B336 shows as a history code, without other data codes, check 7-volt power, ground and data line for intermittent faults. If other data codes are stored, refer to MULTIPLE INTERMITTENT CODES option in this article.

Code B336 Flow Chart, Loss Of IPC Data. Scheme 69

Code B336 Flow Chart, Loss Of IPC Data. Scheme 70

BCM CODE B337 - LOSS OF A/C-HEATER PROGRAMMER DATA

If BCM has lost data communication with A/C-heater programmer and ignition is on, code B337 will set. Fault can be caused by a loss of 12 volts power, ground to programmer or a double open in programmer data line, one on each side of component. During a failure, A/C clutch is disabled and blower motor runs at a constant 6 volts.

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

1. Ensures code is not intermittent.
2. Determines if fault is due to power or ground circuits or data line.
3. Determines if data line fault is due to wiring or programmer.
4. Checks for "IGN. 3" to programmer.
5. Determines if loss of ground is due to programmer, wiring or CPS.

If B337 shows as a history code, without other data codes, check ignition feed, CPS ground, and data circuits for intermittent faults. If other data codes are stored, refer to MULTIPLE INTERMITTENT CODES option in this article.

Code B337 Flow Chart, Loss Of A/C-Heater Programmer Data. Scheme 71

Code B337 Flow Chart, Loss Of A/C-Heater Programmer Data. Scheme 72

BCM CODE B410 - CHARGING SYSTEM CIRCUIT

The generator has fault detection capability built into the regulator. BCM will supply 12 volts to regulator over circuit No. 225 (L terminal) and monitor field voltage of generator by using a PWM signal over circuit No. 23 (F terminal).

Code B410 will set if there is either an open or short to ground on circuit Nos. 23 and 225, a belt break, or if an undervoltage or overvoltage condition exists. If there is a short to ground on circuit No. 225, the "BATTERY NO CHARGE" telltale light will illuminate on the IPC.

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

1. BCM input code BI51 displays generator voltage as "HI" or "LO" depending on voltage state at BCM. Normally with ignition on, engine off, circuit No. 225 will be pulled low by generator and BI51 will read "LO".
2. Checks if "LO" reading is due to circuit No. 225 or generator. If reading changes from "LO" to "HI" when generator is disconnected, circuit No. 225 and BCM are okay.
3. Determines if fault is due to BCM or circuit No. 225.
4. BCM data code BD51 displays amount of generator field activity. Under normal conditions, a reading below 7 percent would indicate a fault in field circuit or BCM.
5. Removing generator connector will determine if fault is due to generator or an open in circuit No. 225 including BCM and interface connector.

If an intermittent condition exists, perform battery and charging system checks to assure proper operation. Also perform a comprehensive visual check of generator wiring and connection.

Code B410 Schematic, Charging System Circuit. Scheme 73

Code B410 Flow Chart, Charging System Circuit. Scheme 74

Code B410, Charging System Circuit (1 Of 2). Scheme 75

Code B410, Charging System Circuit (2 Of 2). Scheme 76

BCM CODE B411 & 412 - BATTERY VOLTAGE LOW OR HIGH

The BCM monitors "IGN 1" voltage on terminal "3C11" as a reference for fuel control. When ignition is on, engine speed is more than 800 RPM and "IGN 1" voltage is less than 10 volts, code B411 is set. If "IGN 1" voltage is more than 16 volts, code B412 is set.

During a failure cruise control will disengage. The cause of codes B411 and B412 should be corrected before diagnosing any other code that has set because high or low voltage can set false codes. A current B411 or B412 code can be observed in BCM data display BD50 outside the range of 10-16 volts.

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

1. BCM data value BD50 displays battery voltage. Normal range is between 10-16 volts.
2. Checks if low voltage reading is caused by circuit or battery. If voltage is less than 10 volts with engine running, BCM and wiring are okay.
3. Checks if low voltage reading is caused by the circuit or BCM. If voltage at BCM is less than 10 volts, BCM is okay.
4. Checks if high voltage reading is caused by generator or the BCM.
5. Checks if charging voltage goes too high with higher engine RPM or electrical load.

If an intermittent code B411 or B412 is being set, observe BCM data value BD50. This voltage reading is monitored from "IGN 1" fuse, fuel reference voltage. If code is being set due to a high current draw from a vehicle component, this can be observed by reading BD50. Operate various components while watching for reading to be less than 10 volts or more than 16 volts. Code B411 may be caused by an intermittent open in circuit No. 39 which may be observed by manipulating the wire to the BCM while watching BD50 for a value less than 10 volts.

Code 411 & 412 Battery Voltage Low Or High. Scheme 77

Code 411 & 412 Battery Voltage Low Or High. Scheme 78

BCM CODE B420 - RELAY CIRCUITS

The BCM operates twilight, retained accessory power, high/low beam and courtesy light relays by providing a ground for the coils. When relay or relays are on, BCM output will be low and when relays are off, BCM output will be high. Code B420 will set if ignition is on and output voltage at BCM is low when a high has been commanded.

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

1. To determine which system has failed, select BCM output function in diagnostics. As individual outputs cycle on and off, observe their actual operation.

Since all 4 groups of relays can cause an intermittent condition, see NOTES ON INTERMITTENTS for courtesy light relay, twilight relays, high/low beam relays, or retained accessory power relays.

Code B420 Schematic, Relay Circuits. Scheme 79

Code B420 Flow Chart, Relay Circuits. Scheme 80

Code B420 Flow Chart, Relay Circuits. Scheme 81

BCM CODE B420 - COURTESY LIGHT RELAY CIRCUIT

If courtesy lights did not cycle on and off when BO04 was selected, then courtesy lights relay set code B420.

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

1. Checks if fault is caused by an open circuit or a short to ground. If courtesy lights are always on, then there is a short to ground in control circuit. If courtesy lights are never on, then there is an open in one of the circuits.
2. Checks if short to ground is due to circuit or BCM.
3. Checks if open circuit is due to circuit or BCM.
4. Checks if open circuit is on power side of relay.
5. Checks is open circuit is on ground side of relay or if relay is at fault.

If an intermittent code B420 is being set, manipulate related wiring in output function and watch for relays to cycle.

Code B420 Schematic, Courtesy Light Relay Circuit. Scheme 82

Code B420 Flow Chart, Courtesy Light Relay Circuit. Scheme 83

Code B420 Flow Chart, Courtesy Light Relay Circuit. Scheme 84

BCM CODE B420 - TWILIGHT RELAYS CIRCUIT

If headlights and parklights did not cycle on and off when BO05 was selected, then twilight relay set code B420.

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

1. Checks if fault is caused by an open circuit or a short to ground. If headlights and parklights are always on, then there is a short to ground in control circuit. If headlights are never on, then there is an open in one of the circuits.
2. Checks if short to ground is due to circuit or BCM.
3. Checks if open circuit is due to circuit or BCM.
4. Checks if open circuit is on power or ground side of relay.

If an intermittent code B420 is being set, manipulate related wiring in output function and watch for relays to cycle.

Code B420 Schematic, Twilight Relays Circuit. Scheme 85

Code B420 Flow Chart, Twilight Relays Circuit. Scheme 86

Code B420 Flow Chart, Twilight Relays Circuit. Scheme 87

BCM CODE B420 - HIGH/LOW BEAM RELAYS CIRCUIT

If high/low beam did not cycle on and off when BO06 was selected, then high/low beam relay set code B420.

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

1. Checks if fault is caused by an open circuit or short to ground. If high beams are always on, then there is a short to ground. If high beams never turn on, then there is an open in one of the circuits.
2. Checks if short to ground is due to circuit or BCM.
3. Checks if open circuit is due to circuit or BCM.
4. Checks if open circuit is on the power or ground side of relay.

If an intermittent code B420 is being set, manipulate related wiring in output function and watch for relays to cycle.

Code B420 Flow Chart, High/Low Beam Relays Circuit. Scheme 88

Note. Use this procedure only if directed here from Code B420 chart, relay circuit. If no relays are working, check for open in circuit 840.

Code B420 Flow Chart, High/Low Beam Relays Circuit. Scheme 89

BCM CODE B420 - RETAINED ACCESSORY POWER RELAYS CKT

If relays could not be heard or felt switching each 3 seconds with BO03 selected, then Retained Accessory Power (RAP) relay circuits are suspect.

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

1. Checks for normal RAP functions, and checks for faults in RAP circuits.

If an intermittent code B420 is being set, manipulate related wiring in output function and watch for relays to cycle.

Code B420 Schematic, Retained Accessory Power Relays Ckt. Scheme 90

Code B420 Flow Chart, Retained Accessory Power Relays Ckt. Scheme 91

Code B420 Flow Chart, Retained Accessory Power Relays Ckt. Scheme 92

BCM CODE B440 - A/C-HEATER AIR MIX DOOR CKT PROBLEM

Code B440 is set by BCM if it is unable to move air mix door. The BCM requests door to move over data circuit to programmer. The programmer then supplies 5 volts from circuit No. 705 to DC motor which drives air mix door. The BCM monitors a feedback pot on DC motor which varies between 0-5 volts, depending on its position.

If door is requested to move, but feedback voltage does not change, BCM stores code B440 to indicate that door is not responding to command. If air mix door is near its hot or cold extreme, the code will not set if door is commanded to move to that extreme. Operation of air mix door can be evaluated in BCM data display by observing actual air mix door position (BCM data code BD23) while changing program number (override value BS01) "PROGRAM NO".

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

1. BCM data value BD23 displays actual air mix door position. Normal range is between 1-99 percent. BCM override value BS01 is for program number.
2. Checks to see if fault could be due to 5-volt reference and ground circuit or sensor circuit.
3. Checks to see if fault is due to programmer or sensor circuit.
4. Checks to see if fault is due to circuit or BCM.

If intermittent code B440 is being set, manipulate related wiring while observing BD23. If failure is induced, door reading will either stop or jump to an extreme value "0%" or "100%". This will help to isolate location of malfunction.

Exit diagnostics. Select maximum heating "90°F" and maximum cooling "60°F" using normal A/C-heater controls, waiting a minimum of 2 minutes in each mode to see if code sets.

Code B440 Schematic, A/C Heater Air Mix Door Ckt Problem. Scheme 93

Code B440 Flow Chart, A/C Heater Air Mix Door Ckt Problem. Scheme 94

Code B440 Flow Chart, A/C Heater Air Mix Door Ckt Problem. Scheme 95

BCM CODE B441 - COOLING FANS PROBLEM

Code B441 is set by BCM if it receives improper cooling fans feedback voltage. Cooling fans control module is designed to change feedback voltage on circuit No. 791 as follows

1. 7 volts if fans have been turned off.
2. Zero volts if fans have been turned on.
3. 7 volts if fans have been turned on and an excessive current draw exists (stalled or shorted fan motors).
4. Zero volts if both fan connectors are open.

The BCM will set code B441 if either of the following conditions exist

1. A) The BCM has commanded fans off, but feedback voltage remains low. The BCM will keep code B441 current for rest of ignition cycle and continue providing a normal control signal to cooling fans control module. The BCM will again test this condition during next ignition cycle to determine if malfunction has become intermittent.
2. B) The BCM has commanded fans on, but feedback voltage remains high. The BCM will command fans off to protect the system from possible stalled or shorted motor condition. If control temperatures (coolant and A/C high side) should drop below turn off points and later require the fans on, the BCM will repeat test to determine if malfunction has become intermittent. Both of the above conditions will result in illumination of "COOLANT TEMP/FAN" display on CCDIC whenever control temperatures require cooling fans operation.

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

1. The cooling fans override feature BS04 can be used to evaluate system operation. If either fan is off when high fans are commanded or if either fan is on when fans off is commanded, appropriate diagnostic path can be followed to isolate malfunction.
2. The cooling fans feedback input BI41 can be used to evaluate the feedback signal being received by BCM. If input does not agree with actual fans operation, circuit No. 791 must be investigated for possible malfunction. If input does agree with commanded fans operation within appropriate time period, then cause of code B441 is not currently present.

If intermittent code B441 is being set, manipulate related wiring while observing cooling fans feedback input BI41, and commanding high fans or fans off in override diagnostic mode. If failure is induced, fans status will not agree with commanded operation. This will help to isolate location of malfunction.

Code B441 Schematic, Cooling Fans Problem. Scheme 96

Code B441 Flow Chart, Cooling Fans Problem (1 Of 2). Scheme 97

Code B441 Flow Chart, Cooling Fans Problem (1 Of 2). Scheme 98

Code B441 Flow Chart, Cooling Fans Problem (2 Of 2). Scheme 99

Code B441 Flow Chart, Cooling Fans Problem (2 Of 2). Scheme 100

From Code B441 (1 Of 2). Scheme 101

BCM CODES B446, B447 & B448 - LOW REFRIGERANT PRESSURE

In the process of controlling compressor clutch, BCM monitors certain system inputs for an indication of low refrigerant charge. If system's refrigerant state of charge should fall below approximately 1/3 of its capacity, the BCM is capable of detecting this condition and will illuminate "LOW A/C REFRIGERANT-A/C COMPRESSOR OFF" on CCDIC panel to warn operator. BCM determines state of charge by low side temperature sensor and low refrigerant pressure switch. Since temperature and pressure are proportionally related in the A/C system, a low temperature is the same as low pressure. In addition to message, the BCM will store a diagnostic code B446, B447 or B448 in memory.

These codes all indicate that a low refrigerant condition was detected. If B447 or B448 is detected, compressor clutch will disengage and remain disengaged until diagnostic codes are cleared.

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

1. BCM input value BI08 displays voltage state of the circuit at BCM.
2. Checks if open circuit reading is caused by circuit or switch.
3. Checks if fault is on ignition side or BCM side of switch circuit.
4. Checks if fault is due to pressure switch or low refrigerant charge.

Codes B446, B447 & B448 Schematic, Low Refrigerant Pressure. Scheme 102

Codes B446, B447 & B448 Flow Chart, Low Refrigerant Pressure. Scheme 103

Note. Ambient temperature must be above 50°F.

Codes B446, B447 & B448 Flow Chart, Low Refrigerant Pressure. Scheme 104

BCM CODE B449 - A/C-HEATER HIGH SIDE TEMPERATURE TOO HIGH

Code is designed to disengage A/C compressor clutch in event high side refrigerant temperature exceeds 199°F (93°C). The A/C compressor will come back on when high side temperature falls below 199°F (93°C).

With engine running and A/C on, enter BCM code BD27. Record temperature displayed during A/C operation.

If code was stored or current temperature exceeds 199°F (93°C) and A/C pressure exceeds 380 psi, possible causes for excessive high A/C head pressure must be checked.

BCM CODE B450 - COOLANT HIGH TEMPERATURE (A/C)

If code EO14 is also stored, repair code EO14 first. Code B450 is designed to disengage A/C compressor clutch if engine coolant temperature exceeds 261°F (126°C), and re-engage when temperature falls below 248°F (120°C). With engine running enter BCM data code BD21. Display will be in degrees Celsius. Record coolant temperature.

Engine overheating may accompany this code. If coolant temperature exceeds normal operating range, check for sources of overheating. If coolant temperature displayed exceeds actual coolant temperature as measured with a radiator coolant temperature tester, sensor may be faulty.

BCM CODE B552 - KEEP ALIVE MEMORY ERROR

Code B552 does not indicate a fault but is a normal occurrence anytime power to BCM has been interrupted. Code cannot be cleared from memory in normal manner. Code can only be cleared if it is not current. Under normal conditions, code will become history by having key in "LOCK", wait 5 seconds and have key in "ON" position. Then, re-enter diagnostics. This code should now be history, and can be cleared in normal manner.

This code will also set if following conditions are met: ignition is cranked; and/or, no system voltage signal to BCM terminal "1C9". The purpose of crank circuit is to signal BCM to shut off when cranking so normal voltage variations during starting do not affect electronic devices.

Code B552 Schematic, Keep Alive Memory Error. Scheme 105

BCM CODE B556 - ODOMETER EEPROM ERROR

Along with code B556, "ERROR" will be displayed in odometer display. EEPROM contains specific vehicle information such as: Vehicle Identification Number (VIN), accumulated vehicle mileage, certain vehicle options and other pertinent information. Information is programmed for the specific vehicle it is installed and CANNOT be exchanged or used in any other vehicle. Replacement EEPROMs must be obtained through an authorized Delco Electronics Service Center.

Note. New EEPROM will have to be adjusted to current mileage by an authorized Delco Electronics Service Center.

EEPROM REPLACEMENT PROCEDURE

1. Remove instrument panel compartment door. Detach and move aside relay bracket assembly and fuse panel. With ignition off, disconnect BCM harness. Loosen BCM to bracket retaining nuts. Remove the BCM.
2. Remove 4 screws from EEPROM access cover. Remove cover. Using rocker type PROM remover, engage one end of carrier and press on vertical bar end of remover. Rock engaged end of EEPROM carrier up as far as possible. Engage opposite end of carrier and repeat process until EEPROM carrier is free of socket.
3. Carefully install new EEPROM (mounted in carrier) into BCM socket while aligning small notch in carrier with small notch in socket. Press on EEPROM (carrier only) until EEPROM is firmly seated in socket. To complete installation, reverse removal procedure.
4. Enter diagnostics and clear BCM code or codes. Start engine and observe odometer display. If "ERROR" continues to display, and EEPROM is properly installed, replace BCM.

Code B556, Odometer EEPROM Error - Location of EEPROM. Scheme 106

Eldorado & Seville BCM Wiring Diagram. Scheme 107