Engine Controls - Tests W/codes - BCM Oldsmobile Toronado Trofeo

DESCRIPTION

Toronado and Trofeo models use several electronic components which can be controlled by the service technician to provide valuable self-diagnostic information. The components are part of an electrical network designed to control various engine and body subsystems. This article will provide a description of the overall electronic network and the on-board diagnostic capabilities which have been designed to aid the service technician in system diagnosing and testing.

At the heart of the computer system is the Body Control Module (BCM). The BCM is located behind the glove box and has an integral microprocessor, which is the center for communication with all other components in the system. All sensors and switches are monitored by the BCM or by one of the following major components

1. Cathode Ray Tube Control (CRTC) (optional equipment)
2. Electronic Control Module (ECM)
3. Electronic Heater and A/C Control Panel (ECCP)
4. Instrument Panel Cluster (IPC)
5. Programmer-Heating and A/C (HVAC)
6. SIR Diagnostic Energy Reserve Module (DERM) controller

The Cathode Ray Tube (CRT) is a touch sensitive color "monitor" located in the climate control/radio center for setting temperature controls and accessing BCM diagnostic features. Non-CRT equipped units have an Electronic Climate Control Panel (ECCP) with LED digital display area for temperature and override mode values. Both CRT and ECCP are used to access BCM diagnostics and display them in the IPC information center's 20 character LED display bar.

OPERATION

A combination of inputs from the major components, sensors and switches, communicate together with the BCM. Various inputs to the BCM combine with program instructions within system memory, providing accurate control over all subsystems involved. When a subsystem circuit exceeds preprogrammed limits, a system malfunction is indicated and certain back-up functions may be provided. The BCM controls subsystems through direct outputs or through data transmitted along the serial data line to one of the other major components. The process of receiving, storing, testing and controlling information is continuous. The data communication also gives the BCM control over the ECM's self-diagnostic capabilities. Between the BCM and the other major components of the computer system, a data line communication process has been incorporated, that allows devices to share information and thereby provides additional control capability.

In order to access and control the BCM self-diagnostic features, 2 electronic components are used, the IPC and the ECCP (or the CRT monitor - optional equipment). See Figs. 1 and 2.

The Toronado/Trofeo "service mode" for diagnostic information incorporates a 20-character Driver Information Center (DIC) display. The DIC display is located on the instrument panel cluster. When a malfunction is sensed by the BCM computer system, one of the driver warning messages is illuminated on the DIC. When the "service mode" is entered, various BCM, ECM or IPC faults can be displayed. In addition to the parameters, fault codes, inputs and outputs, other features such as override commands, snapshot, display VIN and code clearing capabilities can be accessed and displayed when commanded through the CRTM or ECCP.

Certain system malfunctions cause computer controlled diagnostic messages and/or telltales to appear, indicating that service is required. When a subsystem circuit exceeds preprogrammed limits, a system malfunction is indicated and the BCM provides certain back-up functions known as "failsoft." A typical "failsoft" action would be the substitution of a fixed input value when a sensor is detected to be open or shorted.

The CRT monitor or ECC panel becomes the controller by which to enter diagnostics and access BCM self-diagnostics. By pressing or touching the appropriate buttons on the CRT monitor or ECC panel, data messages can be sent to the BCM, requesting specific diagnostic features. This communication process allows BCM to transfer any of its available diagnostic information to the instrument panel's 20 character DIC display during "service mode" operation. When in the override mode of BCM diagnostics, the information is displayed at the ECCP temperature LED display or on the CRT monitor. The following is a list of computer controlled subsystems.

1. Alternator/Starter System
2. Chime
3. Climate Control
4. Compass
5. Courtesy Lights
6. CRT Display
7. Cruise Control
8. Dimming (Lighting)
9. Driver Diagnostics
10. ECM Subsystems
11. Gauges
12. Illuminated Entry
13. Instrument Panel Displays
14. Phone
15. Radio
16. Self-Diagnostics System
17. Trip Data
18. Twilight Sentinel

IPC SEGMENT CHECK

1. Turn ignition switch to the ON position. On non-CRT equipped vehicles, simultaneously push OFF and WARM buttons on the Electronic Climate Control Panel (ECCP). On CRT equipped vehicles, simultaneously push the OFF button and touch WARM key on the CRT monitor control panel (CRTM). (Scheme 194)
2. On both non-CRT and CRT monitor equipped vehicles, continue to depress OFF and WARM button/key until all segments and bulbs of the IPC, the Driver Information Center (DIC) panel and ECCP illuminate. (Scheme 195) When all segments are lit, system has entered self-diagnostic mode. Release OFF and WARM button/key.
3. Illuminating the segments of the IPC, DIC and ECCP ensures all display segments are working properly. If all segments illuminate, proceed to DISPLAYING TROUBLE CODES in this article. Failure of any segment to illuminate may result in inaccurate test results. All inoperative segments of the display must be made to operate before proceeding with self-diagnostic procedures in this article.
4. Partial segment check is possible by depressing TEST button on IPC when vehicle is in Park or Neutral. Holding button depressed will light all vacuum fluorescent displays and all telltales on IPC in order to check for faulty bulbs or light panels.

Scheme 194

Scheme 195

EXIT SELF-DIAGNOSTICS

During self-diagnostic procedures, it is possible to exit service mode without erasing trouble codes. On non-CRT equipped vehicles, exit service mode by depressing BI-LEV button on the ECC panel and turning ignition switch to OFF position. On CRT monitor equipped vehicles, exit service mode by touching RTN key on the CRT monitor panel or exit by turning ignition switch to OFF position.

DISPLAYING TROUBLE CODES

1. The Electronic Control Module (ECM), Body Control Module (BCM), and Supplemental Inflatable Restraint (SIR) trouble codes automatically display after system enters self-diagnostics. ECM trouble codes are displayed first, followed by the BCM trouble codes and then SIR trouble codes.
2. All trouble codes appear in an ascending (3 digit) numerical order. ECM codes are prefixed with the letter "E", BCM Codes prefixed with the letter "B", and SIR codes prefixed with the letter "R".
3. In addition, all trouble codes are followed by the letter "C" or "H". Letter "C" stands for current and indicates a trouble code related fault presently exists. Letter "H" stands for history and indicates the system failure was not present the last time the code was accessed.
4. For example: code E016H is ECM trouble code number 016, set in response to a malfunction that occurred in the past (history). Code B410C is BCM trouble code number 410, set in response to a malfunction that is currently taking place.
5. If no ECM, BCM or SIR trouble codes are stored in memory, respectively, a NO E CODE, NO B CODE or NO R CODE message is displayed. Should the communication link between a component and the ECM or BCM fail, a NO ECM/BCM DATA message will be displayed.
6. Trouble code display can be by-passed at any time by pressing FAN DOWN button on EECP (Touch RTN key on CRT monitor).

BCM TROUBLE CODES

Note. To repeat trouble code display sequence, depress OFF button on ECC panel of NON-CRT equipped vehicles. On CRT equipped vehicles, touch LEVL key on the CRT monitor panel.

CLEARING TROUBLE CODES

See CLEAR CODES under TEST TYPE SELECTION.

MANUAL OPERATION OF SERVICE MODE

Note. Manual operation of service mode system is to be used with the TROUBLE CODE CHARTS section of this article. Prior to using flow charts, it will be necessary to become completely familiar with the procedures in MANUAL OPERATION OF SERVICE MODE.

SYSTEM SELECTION

1. After all trouble codes have been displayed (see DISPLAYING TROUBLE CODES in this article), the "service mode" system can be directed to perform specific system diagnostic tests. Following the trouble code display, the first system available for testing will automatically be displayed. For example: ECM? may now be present on the display.
2. To select the desired system, (ECM, BCM, IPC, or SIR), advance and stop the DIC display as follows: On NON-CRT equipped vehicles, depressing the FAN DOWN button on the ECC panel will cycle the system selection list. When the desired diagnostic system is displayed, depress FAN UP button on ECC panel and the displayed system will be selected for testing.
3. On CRTM equipped vehicles, touching the NO key on the CRT monitor panel will cycle the system selection list. When the desired diagnostic system is displayed on the DIC display panel, touch the YES key on the CRT monitor panel and the displayed system will be selected for testing. (Scheme 194)

Note. To cancel a system selection and activate a repeat of the system selection process, depress the OFF button on the ECC panel of NON-CRT equipped vehicles. On CRTM equipped vehicles, touch the LEVL key on the CRT monitor panel.

TEST TYPE SELECTION

1. After the diagnostic system has been selected for testing, 6 test types are now made available for selection. The menu choices are: CLEAR CODES?, DATA?, INPUTS?, OUTPUTS?, OVERRIDE? and SNAPSHOT?. The DIC display may be showing any one of these 6 test type choices.
2. To advance the display, depress FAN DOWN button on the ECCP of NON-CRT equipped vehicles. On CRTM equipped vehicles, touch NO key on the CRT monitor panel.
3. When the desired test type is displayed, depress the FAN UP button on the ECCP (NON-CRT equipped). On CRTM equipped vehicles, touch YES key on the CRT monitor panel.

Note. To cancel a test type selection and activate a repeat of the test type selection process, depress the OFF button on ECC panel for NON-CRT equipped vehicles or for CRTM equipped vehicles, touch LEVL key on the CRT monitor panel. To exit diagnostics without clearing codes, depress the BI-LEVEL button on ECCP or touch RTN key on the CRT monitor panel.

The 6 test types are explained as follows

CLEAR CODES

Selection of CLEAR CODES? will result in the message CODES CLEAR or CODES NOT CLEAR being displayed, indicating whether the codes were successfully cleared. This message appears for 3 seconds, indicating all stored trouble codes have been erased from that system's memory. After 3 seconds, the display will automatically return to the next test type available for testing.

Note. After a trouble code has been cleared, a complete ignition cycle and possibly a test drive should be made, after which a recheck for the code should be made to ensure code did not reset.

DATA

Data test displays compare the malfunctioning system's present specifications with the specifications of a properly functioning system. DIC displays Data values.

INPUTS

1. Input test displays the voltage level of that circuit tested as HI or LO. Input test display is shown on DIC panel.
2. HI or LO refers to input terminal voltage for the particular circuit. The display also indicates if an input reading has changed since the test was selected. This feature permits technician to activate or deactivate any listed device/circuit and then return to the display to see if voltage reading has changed.
3. If a voltage reading change occurs, an X will appear next to the HI/LO indicator; otherwise a 0 will remain displayed indicating no change occurred. The X will only appear once per selected input. The HI/LO indicator will continue to change as the input changes.

OUTPUTS

Output test displays the voltage level of selected device/circuit as HI or LO. After three seconds, this level will cycle between HI and LO voltage. Output test display is shown on DIC panel.

OVERRIDE

Override test is represented as a percentage of the tested functions' full range during its current operation. This percentage value is displayed in the ECC panel's temperature display area (NON-CRT), or on CRT monitor panel's "service mode" screen. The display will alternate between the override percentage value ("--") and the normal operation value. This alternating display is a reminder that the tested function IS NOT being overridden.

Pressing WARM and COOL buttons simultaneously on ECCP (NON-CRT) begins override of function. Touching SLEW ,L and SLEW ,O keys simultaneously on CRT monitor panel begins override of function. Alternating display will stop, and show override value.

Pressing WARM button increases value, pressing COOL button decreases value (NON-CRT). Touching SLEW ,L key on CRT monitor panel increases value, touching SLEW,O key decreases value.

Normal program control is resumed in one of the following 3 ways

1. 1 - Selection of another override will cancel current override.
2. 2 - Selection of another system (ECM, BCM, IPC or SIR) will cancel current override.
3. 3 - Overriding the value beyond either extreme (0 or 90) will display "----" momentarily before resuming value. Releasing control button while "----" is displayed will resume normal program and display will start alternating.

Override test is unique in that while in override test, another test (i.e. DATA, INPUTS, or OUTPUTS) can be selected and be active at the same time with override test. After selecting override test, press the OFF button (NON-CRT equipped) or touch LEVL key (CRT equipped), to allow selection of another test type. ECC panel (or CRT monitor) will continue to display selected override. By pressing OFF and WARM or COOL buttons at same time (NON-CRT equipped), or by touching LEVL and SLEW keys at the same time (CRT equipped) it is possible to monitor effect of override on different parameters.

To exit diagnostics without clearing codes, depress the BI-LEV button on ECCP (NON-CRT) or touch RTN key on CRT monitor panel.

SNAPSHOT

Snapshot is a test type that will record all BCM or ECM data and inputs at one instant for review at a later time. Snapshot permits a technician triggered recording of specific current ECM/BCM data and input parameters for review at a later time. BCM and ECM have slightly different types of snapshot.

Note. Proceed to ECM or BCM SNAPSHOT after selecting snapshot test type.

EXPLANATION OF SPECIFIC TEST SELECTION

Following test type selection, the first of many specific tests will be made available for selection. The 4 characters of this display represent a test code. The first 2 characters of the test code are alphabetic letters which identify both the system and test type already selected. Study the following examples

1. If the BCM system and DATA test type were selected, BD will be the first 2 characters of the display. BD stands for BCM DATA. The last 2 characters numerically identify the specific test selection. For example: BD51 designates BCM DATA, test 51.
2. If the ECM system and Data test type were selected, ED will be the first 2 characters of the display. ED stands for ECM DATA. The numerals following these 2 characters will represent the particular specific test selection.
3. When BI appears as the first 2 characters of the test code, this signifies the BCM system and INPUT test type were selected. The last 2 characters numerically identify the specific test selection. For example: BI51 designates BCM INPUT, test 51.

MAKING SPECIFIC TEST SELECTION

1. On NON-CRT equipped vehicles, scrolling to a lower specific test number is done by depressing the FAN DOWN button. Scrolling to a higher specific test number is done by depressing the FAN UP button. The system will automatically display the value for whatever specific test number is displayed.
2. On CRT monitor equipped vehicles, scrolling to a lower specific test number is done by touching the NO key on the CRT monitor control panel. Scrolling to a higher number is done by touching the YES key. The system will automatically display the value for whatever specific test number is displayed.

Note. To cancel a specific test type selection and activate a repeat of the specific test type selection process, depress the OFF button on ECC panel of NON-CRT equipped vehicles or touch LEVL key on the CRT monitor control panel of CRT equipped vehicles.

Scheme 196

BCM SNAPSHOT (NON-CRT EQUIPPED VEHICLES)

Note. If directed here from TEST TYPE SELECTION under MANUAL OPERATION OF SELF-DIAGNOSTICS in this article, go to step 2).

1. SNAPSHOT allows the recall of system operating specifications present at the exact time a BCM malfunction code was set. Up to 3 snapshots may be recalled. In addition, one snapshot may be triggered on demand by depressing FAN UP button when DO B SNAP is displayed. To enter snapshot complete the following: Enter self-diagnostics. See ENTERING SELF-DIAGNOSTICS under SELF-DIAGNOSTICS in this article. Display trouble codes stored in memory. See DISPLAYING TROUBLE CODES under SELF-DIAGNOSTICS in this article. Select BCM system for testing. See SYSTEM SELECTION under MANUAL OPERATION OF SELF-DIAGNOSTICS in this article. Select SNAPSHOT test type. See TEST TYPE SELECTION under MANUAL OPERATION OF SELF-DIAGNOSTICS in this article. NOTE: To cancel snapshot test type selection and activate a repeat of the specific test type selection process, depress the OFF button on ECC panel.
2. Immediately following the selection of SNAPSHOT?, the system will display CODE BXXX SNAP SHOT. B stands for BCM. XXX is used here to represent the 3 digit trouble code stored in BCM snapshot.
3. With BXXX displayed, depressing the FAN DOWN button on the ECC panel will permit scrolling through the list of BCM diagnostic codes for which the BCM has stored a snapshot. See BCM TROUBLE CODES under SELF-DIAGNOSTICS in this article for list of BCM trouble codes which may be present in snapshot. NOTE: A trouble code displayed during the trouble code display cycle may NOT be present as a snapshot trouble code. If this is the case, exit SNAPSHOT by depressing the OFF button on the ECCP. This will return the display to the next available system selection.
4. After display of the last BCM trouble code for which a snapshot does exist, pressing the FAN DOWN button on the ECC will result in the DO B SNAP display.
5. Responding to this display by depressing the FAN DOWN button on the ECCP will return the display to the first BXXX SNAP? display. Responding to the DO B SNAP display by depressing the FAN UP button with SNAP DATA? or SNAP INPUTS? displayed, will select that test type for display.
6. At this point the display is controlled as it would be for non-snapshot data and inputs display; however, all values and status information represents memorized vehicle conditions. See EXPLANATION OF SPECIFIC TEST SELECTION and MAKING SPECIFIC TEST SELECTION under MANUAL OPERATION OF SELF-DIAGNOSTICS in this article.
7. Depressing the FAN UP key again with DO B SNAP? displayed will change DIC to display the SNAP DONE message to indicate new information has been stored in memory.

BCM SNAPSHOT (CRT EQUIPPED VEHICLES)

Note. If directed here from TEST TYPE SELECTION, go to step 2).

1. SNAPSHOT allows the recall of system operating specifications present at the exact time a BCM malfunction code was set. Up to 3 snapshots may be recalled. In addition, one snapshot may be triggered on demand by touching YES key when TAKE BCM SNAPSHOT is displayed. To enter snapshot complete the following: Enter self-diagnostics. See ENTERING SELF-DIAGNOSTICS in this article. Display trouble codes stored in memory. See DISPLAYING TROUBLE CODES under SELF-DIAGNOSTICS in this article. Select BCM system for testing. See SYSTEM SELECTION under MANUAL OPERATION OF SELF-DIAGNOSTICS in this article. Select SNAPSHOT test type. See TEST TYPE SELECTION under MANUAL OPERATION OF SELF-DIAGNOSTICS in this article. NOTE: To cancel snapshot test type selection and activate a repeat of the specific test type selection process, touch the LEVL key on the CRT monitor.
2. Immediately following the selection of SNAPSHOT?, the system will display BXXX SNAPSHOT. "B" stands for BCM. XXX is used here to represent the 3 digit code stored in BCM snapshot.
3. With BXXX SNAPSHOT displayed, touching the NO key on the CRT monitor will permit scrolling through the list of BCM diagnostic codes for which the BCM has stored a snapshot. See BCM TROUBLE CODES under SELF-DIAGNOSTICS in this article for list of BCM trouble codes which may be present in snapshot. NOTE: A trouble code displayed during the trouble code display cycle may not be present as a snapshot trouble code. If this is the case, exit SNAPSHOT by touching the LEVL key on the CRT monitor. This will return the display to the next available system selection.
4. After display of the last BCM trouble code for which a snapshot does exist, touching the NO key on the CRT monitor will result in the TAKE BCM SNAPSHOT? display. Responding to this display by again touching the NO key will return the display to the first BXXX SNAPSHOT? display.
5. Responding to the TAKE BCM SNAPSHOT? display by touching the YES key on the CRT monitor with SNAP DATA? or SNAP INPUTS? displayed will select that test type.
6. At this point the display is controlled as it would be for non snapshot data and inputs displays; however all values and status information represent memorized vehicle conditions. See EXPLANATION OF SPECIFIC TEST SELECTION and MAKING SPECIFIC TEST SELECTION under MANUAL OPERATION OF SELF-DIAGNOSTICS in this article.
7. Touching the YES key again with TAKE BCM SNAPSHOT? displayed will change DIC to display the SNAP DONE message to indicate new information has been stored in memory.

ECM SNAPSHOT (NON-CRT EQUIPPED VEHICLES)

Note. If directed here from TEST TYPE SELECTION under MANUAL OPERATION OF SELF-DIAGNOSTICS in this article, go to step 2).

1. SNAPSHOT allows the recall of system operating specifications present at the exact time an ECM malfunction code was set. Up to 3 snapshots may be recalled. In addition, one snapshot may be triggered on demand. To enter snapshot, complete the following: Enter self-diagnostics. See ENTERING SELF-DIAGNOSTICS under SELF-DIAGNOSTICS in this article. Display trouble codes stored in memory. See DISPLAYING TROUBLE CODES under SELF-DIAGNOSTICS in this article. Select ECM system for testing. See SYSTEM SELECTION under MANUAL OPERATION OF SELF-DIAGNOSTICS in this article. Select SNAPSHOT test type. See TEST TYPE SELECTION under MANUAL OPERATION OF SELF-DIAGNOSTICS in this article. NOTE: To cancel snapshot test type selection and activate a repeat of the specific test type selection process, depress the OFF button on ECC panel.
2. Immediately following the selection of SNAPSHOT?, the system will display the message SNAP DONE. This message appears for 3 seconds to indicate all ECM data and inputs have been stored in memory. Following this 3 second information storage verification, the display will automatically proceed to the first available snapshot test type (i.e., SNAP DATA? or SNAP INPUTS?).
3. At this point, depressing the FAN DOWN button will display the next available snapshot test type. Display may be toggled between SNAP DATA? and SNAP INPUTS?.
4. Depressing the FAN UP button with SNAP DATA? or SNAP INPUTS? displayed will select that particular test type.
5. At this point, the display is controlled as it would be for non-snapshot data and inputs displays; however, all values and status information represents memorized vehicle conditions. See EXPLANATION OF SPECIFIC TEST SELECTION and MAKING SPECIFIC TEST SELECTION under MANUAL OPERATION OF SELF-DIAGNOSTICS in this article.
6. Depressing the FAN UP key with ECM SNAPSHOT? displayed will display the SNAPSHOT TAKEN message to indicate that new information has been stored in memory.

Scheme 197

ECM SNAPSHOT (CRT EQUIPPED VEHICLES)

Note. If directed here from TEST TYPE SELECTION, go to step 2).

1. SNAPSHOT allows the recall of system operating specifications present at the exact time an ECM malfunction code was set. Up to 3 snapshots may be recalled. In addition, one snapshot may be triggered on demand. To enter snapshot, complete the following: Enter self-diagnostics. See ENTERING SELF-DIAGNOSTICS under SELF-DIAGNOSTICS in this article. Display trouble codes stored in memory. See DISPLAYING TROUBLE CODES under SELF-DIAGNOSTICS in this article. Select BCM or ECM system (as desired) for testing. See SYSTEM SELECTION under MANUAL OPERATION OF SELF-DIAGNOSTICS in this article. Select SNAPSHOT test type. See TEST TYPE SELECTION under MANUAL OPERATION OF SELF-DIAGNOSTICS in this article. NOTE: To cancel snapshot test type selection and activate a repeat of the specific test type selection process, touch the LEVL key on the CRT monitor control panel.
2. Immediately following the selection of SNAPSHOT?, the system will display the message SNAP DONE. This message appears for 3 seconds to indicate all ECM data and inputs have been stored in memory. Following this 3 second information storage verification, the display will automatically proceed to the first available snapshot test type (i.e., SNAP DATA? or SNAP INPUTS?).
3. At this point, touching the NO key on the CRT monitor panel will display the next available snapshot test type. Display may be toggled between SNAP DATA? and SNAP INPUTS?.
4. Touching the YES key with SNAP DATA? or SNAP INPUTS? displayed will select that particular test type. From this point, the display is controlled as it would be for non-snapshot data and inputs displays; however, all values and status information represents memorized vehicle conditions. See EXPLANATION OF SPECIFIC TEST SELECTION and MAKING SPECIFIC TEST SELECTION under MANUAL OPERATION OF SELF DIAGNOSTICS in this article.
5. Touching the YES key on the CRT monitor panel with ECM SNAPSHOT? displayed will display the SNAPSHOT TAKEN message to indicate that new information has been stored in memory.

STATUS LIGHT INDICATORS

During self-diagnostics, the status light display on ECC Panel or CRT monitor is used to indicate switchable parameter status. Each parameter status is indicated by its status light being turned ON or OFF. Status light indicators are relative to system level being tested (BCM or ECM). (Scheme 198)

The following are brief summaries of each systems status light indicators, starting with the ECM status light indicators

1. LOOP light (CRT equipped) or HIGH light (ECCP equipped) is ON when ECM is in closed loop fuel control. Light comes ON only after coolant and O2 sensors reach operating temperature.
2. TCC light (CRT equipped) or MED light (ECCP equipped) only indicates whether operation is enabled or disabled by ECM. Actual working operation depends on TCC system being in working order.
3. Oxy light (CRT equipped) or LOW light (ECCP equipped) stays ON when oxygen sensor signals rich exhaust condition to ECM. Light will flash ON and OFF during warm engine, steady throttle, and proper fuel mix condition.
4. EGR light (CRT equipped) or LOWER ARROW light (ECCP equipped) is ON when ECM is directing one of the 3 EGR solenoids to be ON. Light will be OFF if no EGR solenoids are ON as during idle condition.
5. 4th Gear light (CRT equipped) or OFF light (ECCP equipped) will be ON when ECM senses 4th gear pressure switch open. Light should only be on in 4th gear.
6. 3rd Gear light (CRT equipped) or AUTO light (ECCP equipped) will be ON when ECM senses 3th gear pressure switch open. Light should only be on in 3rd or 4th gear.
7. 2nd Gear light (CRT equipped) or "°C" light (ECCP equipped) will be ON when ECM senses 2nd gear pressure switch open. Light should only be on in 2nd, 3rd or 4th gear.
8. A/C Compressor Command UPPER ARROW (ECCP equipped) or COMP light (CRT equipped) will be ON only when ECM allows A/C clutch engagement through A/C relay. Light will also be ON if BCM requests ECM to turn clutch ON during test sequence. Light should be OFF if ECM commands disengagement.

The following are brief summaries of BCM system status light indicators

1. PRESS light (CRT equipped) or LOWER ARROW light (ECCP equipped) will be ON if BCM senses low refrigerant pressure switch is open. Light will remain OFF if A/C system is fully charged and operational. (However, light will come ON when outside vehicle ambient temperature is less than -5°F (-21°C), this is due to temperature-pressure relationship of R-12 refrigerant.)
2. OFF light (ECCP equipped) or REC light (CRT equipped) will be ON when BCM commands air recirculation.
3. MED light (ECCP equipped) or A/C light (CRT equipped) will be ON when BCM commands air flow out A/C vents. Light should also be ON in A/C and BI/LEVEL modes.
4. AIR UP light (CRT equipped) or LOW light (ECCP equipped) will be ON when BCM commands air flow out defroster outlets. Light should also be ON in defrost and A/C modes.
5. AIR DOWN light (CRT equipped) or HIGH light (ECCP equipped) will be ON when BCM commands air flow out floor outlets. Light should be ON in heater mode.
6. Left side AUTO light (ECCP equipped) or COMP light (CRT equipped) will be ON when BCM requests ECM to engage A/C compressor clutch.

Scheme 198

DATA DISPLAY CODES

Brief summary of each DATA parameter is as follows

BCM DATA PARAMETERS

1. BD20 Commanded blower voltage (BLWR VOLTS) READ in volts from 0 to 18.0.
2. BD21 Coolant temperature (COOLANT TP) displayed in degrees Celsius (°C) from -40 to 151. This value is sent from ECM to BCM. If circuit malfunctions, ECM will send BCM a "failsoft" value for display.
3. BD22 Commanded air mix door position (COM MIX DR) displayed in percent. Value close to 0% represents cold air mix and value close to 100% represents warm air mix.
4. BD23 Actual air mix door position (ACT MIX DR) displayed in percent. This value should follow commanded air mix door position (BD22) except when door is commanded beyond its mechanical limits of travel.
5. BD24 Air delivery mode (AIR MODE) displayed as number from 0 to 12. Each number is code which represents following air delivery modes: 0 - Auto-Recirc Upper outlets 1 - Auto-outside Upper outlets 2 - Auto-Bi-Level outlets 3 - Auto-Heater-Defog outlets 4 - Auto-Lower outlets 5 - OFF 6 - Normal purge 7 - Cold (DEF) purge 8 - Defog 9 - Forced (FAN) Lower outlets 10 - Forced (FAN) Upper outlets 11 - Forced (FAN) Bi-level outlets 12 - Forced (FAN) De-fog outlets
6. BD25 In-car temperature (IN CAR TP) displayed in degrees Celsius (°C) from -40 to 102.
7. BD26 Actual outside temperature (OUTSIDE TP) displayed in degrees Celsius (°C) from -40 to 93. This value represents actual sensor temperature and is not buffered by software.
8. BD27 A/C High side temperature (HI SIDE TP) (condenser output) displayed in degrees Celsius (°C) from -40 to 215.
9. BD28 A/C Low side temperature (LO SIDE TP) (evaporator input) displayed in degrees Celsius (°C) from -40 to 93.
10. BD32 Sunload temperature sensor (SUN TP) displayed in degrees Celsius (°C) from -40 to 102.
11. BD40 Actual fuel level (FUEL LEVEL) read in gallons between 0 to 17.0. Value represents actual sensor position and is not restricted by features used to eliminate fuel slosh affects on IPC display value.
12. BD41 PRNDD21 (PRND321) displayed as four digit binary number as follows: P - 0110 R - 0011 N - 1010 D - 1001 D - 0000 2 - 0101 1 - 1100
13. BD42 Dimming pot (DIM POT) displayed in percent. Value close to 0% represents maximum dimming and value close to 100% represents maximum brightness.
14. BD43 Twilight delay pot (TWI POT) displayed in percent. Value close to 0% represents minimum delay time and value close to 100% represents maximum delay time.
15. BD44 Twilight Photocell (TWI PHOTO) displayed in percent. Value close to 0% represents daylight and value close to 100% represents darkness.
16. BD45 Phone Mode (PHONE MODE) displayed as number from 0 to 7, indicating the state of phone system. (Only used with factory installed phone.) 0 - No phone system present 1 - Phone power off, ignition on 2 - Phone power on 3 - Phone power on, no service 4 - Roam service 5 - Call in progress 6 - Call received 7 - System problem
17. BD50 Battery voltage (BATT VOLTS) read in volts between 0 and 25.5.
18. BD51 Generator field (GEN F TERM) displayed in percent. Value close to 0% represents minimum regulator on time and value close to 100% represents maximum regulator on time.
19. BD60 Vehicle speed (MPH) displayed in miles per hour from 0 to 159.
20. BD61 Engine speed (RPM) displayed in RPM from 0 to 6375.
21. BD70 Cruise servo position (C/C FBK) displayed in percent from 0 to 100%. Value close to 0% represents at rest position and value close to 100% represents wide open throttle.
22. BD71 Oil pressure sensor (OIL PRESS) displayed in psi from 0 to 80.
23. BD72 DIS KEY displays unique code (defined below) received at the BCM from switch pod for each switch held. This code is for communication between computers and DOES NOT MATCH printed numbers on keys. This parameter is on NON-CRT vehicles only. 2 - Disp ON/OFF 3 - System Monitor 4 - Econ 5 - Fuel 6 - Range 7 - Speed 8 - Eng Data 9 - Date 10 - Dist 11 - ETA 12 - Elap Time 13 - E/M 14 - Reset/Enter 15 - Odo/Trip 16 - Trip Reset
24. BD98 Ignition cycle (IGN CYCLES) value is the number of times that the BCM has been turned OFF since BCM trouble code was last detected. After 99 ignition cycles, where each OFF, CRANK, OFF cycle counts as 2, without any malfunction being detected, all BCM codes are cleared.
25. BD99 BCM PROM I.D. (PROM ID) displayed as number, up to four digits long, which can be used to verify that proper PROM was installed in BCM.

FOR CRT Control CODE

1. CD99 CRTC PROM I.D. (PROM ID) displayed as number up to four digits long, which can be used to verify that proper PROM was installed in the CRT monitor.

INPUT DISPLAY CODES

Brief summary of each systems INPUT parameters is as follows.

BCM INPUT PARAMETERS

1. BI01 PANEL LAMP switch display is LO when panel lamp switch is in off position.
2. BI02 PARK LAMP switch display is LO when parklamp switch is in off position.
3. BI03 Driver door ajar switch (LT DR AJAR) display is LO when drivers front door is ajar.
4. BI04 Passenger door ajar switch (RT DR AJAR) display is LO when passenger's rear door is open.
5. BI05 DOOR JAMB switch display is LO when any door is open.
6. BI06 Door handle switch (DOOR HNDLE) display is momentarily LO when either outside door handle button is depressed.
7. BI08 Low refrigerant pressure switch (A/C PRESS) display is LO when system is low on refrigerant.
8. BI09 Washer fluid level switch (WASH FLUID) display is LO when vehicle is low on washer fluid.
9. BI17 TURN SIGNAL input (BLANK DISPLAY) is HI when turn signal switch is in OFF position. When either directional is ON, input will toggle between LO and HI, with bulb illuminating in HI state.
10. BI18 Brake pressure (BRK PRESS) signal is LO when ABS brake pressure is below set value . This input has no meaning on non-ABS equipped vehicles.
11. BI21 Low brake fluid (BRK FLUID) display is LO when brake fluid is low.
12. BI22 PARK BRAKE switch display is LO when parking brake is applied.
13. BI24 FOGLAMP switch display is LO whenever switch is pressed.
14. BI25 SEAT BELT switch display is HI when drivers seatbelt is fastened.
15. BI51 GENERATOR FEEDBACK (I-TERM) display is LO when there is generator problem or engine is not running.
16. BI71 CRUISE CONTROL BRAKE SWITCH display is HI when cruise ON/OFF switch is ON and brake pedal is not depressed .
17. BI75 CRUISE CONTROL ON/OFF SWITCH display is HI when cruise ON/OFF switch is ON and set/coast switch is depressed.
18. BI76 CRUISE CONTROL SET/COAST SWITCH display is HI when cruise ON/OFF switch is ON and set/coast switch is pushed.
19. BI77 CRUISE CONTROL RESUME/ACCEL SWITCH display is HI when cruise ON/OFF switch is ON and Resume/Accel switch is pushed.
20. BI78 HEADLAMPS display is HI whenever headlamp switch is ON.
21. BI82 TWILIGHT display is LO whenever headlamp switch is ON.
22. BI83 HI BEAM display is LO whenever hi beam switch is ON.
23. BI88 LOW OIL display will be HI when engine oil level is low.

IPC INPUT PARAMETERS

1. II05 ENG/MET display is LO whenever english-metric button is pressed (CRT ONLY).
2. II06 SYS MON display is LO whenever system monitor button is pressed (CRT ONLY).
3. II07 ODO/TRIP display is LO whenever trip odometer button is pressed (CRT ONLY).
4. II08 FUEL GAUGE display is LO whenever gauge button is pressed (DIGITAL CLUSTER ONLY).
5. II09 TACH display is LO whenever tachometer button is pressed (DIGITAL CLUSTER ONLY).
6. II10 TRIP RESET display is LO whenever trip reset button is pressed.

OUTPUT DISPLAY CODES

Brief summary of each systems OUTPUT parameters is as follows.

BCM OUTPUT PARAMETERS

1. BO00 CYCLE NONE will display and will not show HI or LO. This is normal resting code where no outputs will be cycled.
2. BO01 Cruise control vent solenoid (C/C VENT) display is HI when vent solenoid is ON (energized). Cruise ON/OFF switch must be ON for output to cycle.
3. BO02 Cruise control vacuum solenoid (C/C VAC) display is HI when vacuum solenoid is ON (energized). Cruise ON/OFF switch must be ON for output to cycle.
4. BO04 Courtesy lamps (COURT LMPS) display is LO when relay is ON (energized).
5. BO05 Twilight relay (TWILIGHT) display is LO when relays are ON (energized).
6. BO10 CHIME 1 display is LO when fast chime is ON (sounding).
7. BO11 CHIME 2 display is LO when slow chime is ON (sounding).
8. BO12 DRL FG LMP display is LO when foglights (DRL) are ON.
9. BO13 DIS CLOCK display is LO when clock line voltage is LO.

OVERRIDE DISPLAY CODES

Brief summary of each OVERRIDE parameter is as follows.

Note. For CRT equipped vehicles, substitute SLEW 67,L and SLEW 67,O keys for WARM or COOL buttons in following parameters.

BCM OVERRIDE PARAMETERS

1. BS00 The NONE display will not show any value in display area on ECCP or CRT Monitor, as no overrides are active at this point. This is normal resting code where no overrides will be controlled. This code can be used to stop override control without having to go back to system selections.
2. BS01 PROGRAM NUMBER - As heating and A/C operating conditions change, program number will automatically change. Program number can be manually overridden using WARM and COOL buttons. WARM button will increase number at controlled rate until MAX HEAT mode value of "99" is reached. COOL button will decrease number at controlled rate until MAX A/C mode value of "0" is reached. Manual override will continue until override code is canceled. This manual override control allows technician to alter and observe reactions of system change on other BCM data parameters.
3. BS03 BULB DIM - As dimming switch position is moved, incandescent dimming number will automatically change (only if exterior lights are ON). Using override controls, WARM and COOL buttons, automatic dimming can be manually controlled. Using "99" to represent maximum brightness and "0" to represent maximum dimming of incandescent lighting, (exterior lights need not be on when overriding dimming).
4. BS05 C/C SERVO - With engine OFF and ignition ON. Cruise control switch must be ON to override automatic calculations for cruise control. Using "99" to represent maximum cruise position (WOT) and "0" to represent minimum cruise position (closed throttle). Manual override will continue until override code is canceled. This manual override control allows technician to alter cruise control position and observe reactions of data value for cruise servo position (BD70). The 2 parameters should agree within 3% except when servo is commanded beyond its mechanical travel limits. Remember that there is ONLY enough vacuum in storage tank to operate servo ONCE.
5. BS06 BLOWER SPEED - WARM button will override control of HVAC blower to full speed (99 representing maximum blower) and COOL button will slow blower to minimum speed (0 representing blower off).
6. BS07 OPTION CONTENT No. 1 - Option content No. 1 (OPTION 1) displayed as number from 0 to 255. Each number is a code which represents option content. BCM uses this value to determine how to operate the displays and electronic controls. Incorrect option values cause many different problems. To determine proper option value add up following options that vehicle is equipped with: U.S. vehicle (not Canadian or export model) - 128 Analog cluster - 64 Export displays (export car, option code NM8) - 32 Compass (option code UC3) - 4 Take total of actual options from above list and compare it with OPTION 1 value. If the two are different, correct OPTION 1 value using following procedure. To change option content number press WARM or COOL button for override control until desired number appears, (corresponding to total of actual options). Next, press and hold LOWER air mode and DEFROST buttons simultaneously for 5 seconds, (CRT equipped vehicles use DEFROST AND Rear DEFOG keys). This will reprogram BCM EEPROM to number of options displayed on the IPC.
7. BS08 OPTION CONTENT No. 2 (OPTION 2) is displayed as number from 0 to 255. Each number is a code which represents option content. BCM uses this value to determine how to operate the displays and electronic controls. Incorrect option values cause many different problems. To determine proper option value add up following options that vehicle is equipped with: Oil level sensor (all vehicles) - 64 Anti-lock brakes (option code JL9) - 16 Washer fluid level sensor (all vehicles) - 8 Trofeo model - 4 Take total of actual options from above list and compare it with OPTION 2 value. If the two are different, correct OPTION 2 value using following procedure. To change option content number press WARM or COOL button for override control until desired number appears, (number corresponding to total of actual options) Next, press and hold both LOWER air mode and DEFROST buttons for 5 seconds, (CRT equipped vehicles use DEFROST and Rear DEFOG keys). This will reprogram BCM EEPROM to number of options displayed on the IPC.

CHART A-1, NO SERVICE ENGINE SOON LIGHT

The SERVICE ENGINE SOON (SES) light is located in the IPC. Light is powered by Ignition 1, circuit No. 39 and ECM completes system ground to turn light ON. With ignition ON, engine not running, light should be ON. If with engine running light is ON steady, this indicates an ECM code is set. When system diagnostics are entered, light should flash, indicating service mode of ECM has been entered. The system monitor button does not affect SERVICE ENGINE SOON light.

Note. Test numbers refer to numbers on diagnostic chart.

Test Number 1) This step splits circuit into 2 sections. SERVICE ENGINE SOON light illuminating after grounding ALDL terminal "D" indicates open is on ECM side of circuit. SERVICE ENGINE SOON light staying OFF would indicate fault is on IPC side of circuit.

Test Number 2) With test light, check circuit No. 39 to ensure voltage is available to SES light bulb. Check body ignition 1 fuse No. 14 if test light does not light.

Test Number 3) If test light DID NOT illuminate when connected between ECM terminal BA 6 and ground, ECM is not getting power. This is result of an open or short to ground (blown fuse) in circuit No. 439.

Test Number 4) This step checks for open in IPC or circuit No. 419. IPC terminal D2 is 12 volts. When test light connected between terminals D2 and C9 illuminates, it indicates that circuit No. 419 is complete through ALDL terminal D , which has been grounded.

Test Number 5) This step checks for open in ECM or circuit No. 419. If test light illuminates when backprobed to ECM harness terminal YC11 (Brown/White wire), fault is from poor contact at terminal YC11 or a faulty ECM.

Diagnostic Aids

An intermittent fault may be caused by poor connection, rubbed through wire insulation or wire broken inside insulation.

1. Check for poor connection at ECM terminal YC11 or IPC connector. Inspect wire harness connectors for backed out terminals, improper mating, broken connector locks, improperly formed or damaged terminals and poor terminal to wire crimp connection.
2. Inspect wire harness thoroughly for damage. A flickering test light indicates intermittent fault location.

Chart A-1: Circuit Diagram. Scheme 199

Chart A-1: Flow Chart No SES Light. Scheme 200

CHART A-2, SERVICE ENGINE SOON LIGHT WILL NOT GO OUT OR FLASH

The SERVICE ENGINE SOON (SES) light is located in the IPC. Light is powered by Ignition 1, circuit No. 39 and ECM completes system ground to turn light ON. With ignition ON, engine not running, light should be ON. If with engine running light is ON steady, this indicates an ECM code is set. When system diagnostics are entered, light should flash, indicating service mode of ECM has been entered. The system monitor button does not affect SERVICE ENGINE SOON light.

Note. Test numbers refer to numbers on diagnostic chart.

Test Number 1) This step verifies SERVICE ENGINE SOON light remains ON with engine running and no ECM codes displayed.

Test Number 2) Disconnecting ECM harness Yellow connector determines if short to ground is in ECM or elsewhere in circuit. If SERVICE ENGINE SOON light remains ON, fault is not in ECM.

Test Number 3) Check for short to ground in the IPC or in circuit No. 419. If test light illuminates when connected between IPC harness connector terminals C9 and D2, fault is a short to ground in circuit No. 419.

An intermittent fault may be caused by poor connection, rubbed through wire insulation or wire broken inside insulation.

1. Check for poor connection at ECM terminal YC11 or IPC connector. Inspect wire harness connectors for backed out terminals, improper mating, broken connector locks, improperly formed or damaged terminals and poor terminal to wire crimp connection.
2. Inspect wire harness thoroughly for damage. A flickering test light indicates intermittent fault location.

Chart A-2: Flow Chart No SES Light Will Not Go Out Or Flash. Scheme 201

NON-CRT EQUIPPED SELF-DIAGNOSTIC SYSTEM CHECK

The Self-Diagnostic System Check is an organized approach for identifying problem caused by on-car computer controlled electronics. Understanding this chart and using it correctly will reduce diagnosis time and prevent unnecessary replacement of components. If you have not reviewed the basic information on how to use computer self-diagnostics, go to beginning of this article.

Non-CRT Equipped Self-Diagnostic System Check. Scheme 202

CHART A, LOSS OF IPC DISPLAY NON-CRT EQUIPPED

Loss of IPC display and messages can result from following

1. Loss of 12 volts to IPC
2. Loss of ground to IPC
3. Loss of 7 volts
4. Ground in 7 volt circuit No. 807
5. Internal fault in CPS, BCM or IPC

Note. Test numbers refer to numbers on diagnostic chart.

Test Number 1) This step checks to see if BCM is awake. If BCM is not awake, cause of blank display is power and/or ground related.

Test Number 2) This step checks CPS power and ground sources.

Test Number 3) This step checks to see if CPS lost power or ground.

Test Number 4) This step checks for ignition and CPS power, and ground to IPC. With Ignition ON, battery voltage should be present at these terminals.

Test Number 5) This step checks if fuse No. 5 is feeding power to CPS.

Test Number 6) This step checks if fuse No. 5 is blown due to short to ground in circuit No. 812.

Test Number 7) This step checks if short to ground is inside component or in circuit.

Test Number 8) This step checks if IPC is receiving 7 volts from CPS.

Chart A: Circuit Diagram. Scheme 203

Chart A: Flow Chart Loss of IPC Display Non-CRT Equipped. Scheme 204

CHART A-1, CENTRAL POWER SUPPLY (CPS) NON-CRT EQUIPPED

CPS provides filtered 12 volts, 7 volts, and ground for most major computers in system. BCM is continuously supplied 12 volts from CPS. When "wake-up" signal (such as opening door or turning ignition ON) is received at BCM, 12 volt signal is sent from BCM to CPS to turn ON 7 volt power supply. The 7 volts power various computers that control serial data communications.

The BCM needs a constant 12 volts from CPS and a good ground to function properly. BCM must supply wake-up signal to activate 7 volt supply in CPS.

Note. Test numbers refer to numbers on diagnostic chart.

Test Number 1) This step checks for wake-up signal back to CPS. If test light is illuminated, wake-up signal is occurring and fault is in 7 volt circuit. No illumination of test light indicates that wake-up is NOT occurring.

Test Number 2) This step checks if CPS is providing 7 volts.

Test Number 3) This step checks for source of short by testing all 7 volt circuits and components for short to ground.

Test Number 4) This step checks 12 volt power circuit from CPS to BCM.

Test Number 5) This step checks BCM for 12 volts into itself and for wake-up voltage coming out of BCM.

Test Number 6) This step checks for source of ignition at BCM. Ignition is wake-up signal source.

Test Number 7) This step checks BCM for crank signal. If 12 volts are on terminal 1C9 (crank circuit), BCM goes down and brings CPS down with it.

Chart A-1: Flow Chart Central Power Supply (CPS) Non-CRT Equipped. Scheme 205

CHART B, LOSS OF SERIAL DATA NON-CRT EQUIPPED

IPC indicates loss of serial data communication by displaying the message ELECTRICAL PROBLEM. All other segments are blank. If display is fully illuminated and ELECTRICAL PROBLEM message is displayed, enter diagnostics and proceed to appropriate code chart. Do not use CHART A. Loss of serial data communications can occur for the following reasons

1. Short to ground anywhere in circuit No. 800
2. Short to voltage anywhere in circuit No. 800
3. Two opens in circuit No. 800
4. Loss of 7 volt supply which powers serial communication
5. Internal BCM or IPC fault

Note. Test numbers refer to numbers on diagnostic chart.

Test Number 1) This step checks to see if ECC head has lost data communication along with IPC.

Test Number 2) Since IPC has lost data communications, shorting terminal M at ALDL connector should NOT remove data communications from ECC head. If this does happen, IPC is receiving data but is unable to communicate due to poor connection or an internal problem.

Chart B: Circuit Diagram. Scheme 206

Chart B: Flow Chart Loss of Serial Data Non-CRT Equipped. Scheme 207

CHART C, LOSS OF ECC COMMUNICATIONS NON-CRT EQUIPPED

When ECC communications are lost service diagnostics usually cannot be entered, but a quick scan of panel will usually help isolate source of fault. ECCP is powered by ignition. If power source is lost the secondary display will usually display segment check. Loss of serial data will result in 3 dashes being shown on panel VF display. This indicates power and ground are OK. If the panel displays normal outside or interior set temperature, power, ground and serial communications are being received thus panel replacement is indicated.

Note. Test numbers refer to numbers on diagnostic chart.

Test Number 1) This step checks for power and ground to panel. Test light should be ON for both power to ground checks.

Test Number 2) This step checks for serial data voltage. Normal voltage should be above 1 volt and varying. Steady voltage indicates second open exists, or ALDL cover is off.

Chart C: Flow Chart Loss of ECC Communications Non-CRT Equipped. Scheme 208

CHART D, LOSS OF COMMUNICATIONS NON-CRT EQUIPPED

Note. Test numbers refer to numbers on diagnostic chart.

Test Number 1) Zero volts indicate an open or grounded data line.

Test Number 2) This step checks for short to ground on data line.

Test Number 3) Since ECCP displays were lost, an open must exist between BCM and ECCP. This step determines which side of ECM open is on.

Chart D: Flow Chart Loss of Communications Non-CRT Equipped. Scheme 209

CHART D-1, GROUNDED SERIAL DATA CIRCUIT NON-CRT EQUIPPED

With grounded serial data circuit BCM will not be able to communicate with any other devices in system. Voltage measured anywhere along circuit will be zero. Display on IPC will be ELECTRICAL PROBLEM and ECC will display dashes "---".

Note. Test numbers refer to numbers on diagnostic chart.

Test Number 1) This step splits system in half to help isolate the source of grounded serial data line. If taking ECM out of system allows both halves of serial data line to rise above one volt the source of short has been located.

The remaining steps of chart follow same pattern in that the components are removed from serial data line until normal voltage range is again measured. When section of circuit is isolated, a simple check of wire for short to ground differentiates between a grounded wire or a ground in the device remote.

Chart D-1: Circuit Diagram. Scheme 210

Chart D-1: Flow Chart Grounded Serial Data Circuit Non-CRT Equipped. Scheme 211

CHART D-2, SERIAL DATA CIRCUIT SHORTED TO VOLTAGE, NON-CRT EQUIPPED

With shorted serial data circuit BCM will not be able to communicate with other devices in system. Voltage measured anywhere along circuit will be above 5 volts. IPC will display ELECTRICAL PROBLEM.

Note. Test numbers refer to numbers on diagnostic chart.

Test Number 1) This step splits system in half to help isolate source of short in serial data line. If taking ECM out of system allows both halves of serial data line to fall below 5 volts, source of short was in ECM.

The remaining steps follow same pattern in that components are removed from serial data line until normal voltage range is again measured.

Chart D-2: Flow Chart Serial Data Circuit Shorted to Voltage Non-CRT Equipped. Scheme 212

COLOR CRT SELF-DIAGNOSTIC SYSTEM CHECK - CRT EQUIPPED

The Self-Diagnostic System Check is an organized approach for identifying problem caused by on-car computer controlled electronics. Understanding this chart and using it correctly will reduce diagnosis time and prevent unnecessary replacement of components. If you have not reviewed the basic information on how to use computer self-diagnostics, go to beginning of this article.

Color CRT Self-Diagnostic Terminal Id. (CRT Equipped). Scheme 213

Color CRT Self-Diagnostic System Flow Chart (CRT Equipped). Scheme 214

CHART A, LOSS OF IPC DISPLAY (CRT EQUIPPED)

Loss of IPC display and messages can result from the following

1. Loss of 12 volts to IPC
2. Loss of ground to IPC
3. Loss of 7 volts to IPC
4. Ground in 7 volt circuit No. 807
5. Internal BCM or IPC fault

Note. Test numbers refer to numbers on diagnostic chart.

Test Number 1) This step checks to see if BCM is awake. If not awake, the cause of blank display is power and ground related.

Test Number 2) This step checks CPS power and ground sources.

Test Number 3) This step checks to see if CPS lost power or ground.

Test Number 4) This step checks for ignition source, CPS power and ground to IPC. With ignition ON, battery voltage should be present at listed terminals.

Test Number 5) This step checks if fuse No. 5 feeds power to the CPS.

Test Number 6) This step checks to see if fuse No. 5 failure is from a short to ground in circuit No. 812.

Test Number 7) This step checks to see if short to ground is inside a component or in circuit itself.

Test Number 8) This step checks to see if IPC is receiving 7 volts from CPS.

Chart A: Flow Chart Loss of IPC Display (CRT Equipped). Scheme 215

CHART A-1, CENTRAL POWER SUPPLY (CPS) CHECK - CRT EQUIPPED

CPS provides filtered 12 volts, 7 volts, and ground for most of major computers in system. BCM is continuously supplied 12 volts from CPS. When "wake-up" signal (such as opening door or turning ignition ON) is received at BCM, 12 volt signal is sent from BCM to CPS to turn ON 7 volt power supply. The 7 volts power various computers that control serial data communications.

The BCM needs a constant 12 volts from CPS and a good ground to function properly. BCM must supply wake-up signal to activate 7 volt supply in CPS.

Note. Test numbers refer to numbers on diagnostic chart.

Test Number 1) This step checks for wake-up signal back to CPS. If test light is ON, wake-up signal is occurring and fault is in 7 volt circuit. No light indicates that wake-up is NOT occurring.

Test Number 2) This step checks if CPS is providing 7 volts.

Test Number 3) This step checks for source of short by testing all 7 volt circuits and components for short to ground.

Test Number 4) This step checks 12 volt power circuit from CPS to BCM.

Test Number 5) This step checks BCM for 12 volts into itself and for wake-up voltage coming out of BCM.

Test Number 6) This step checks for source of ignition at BCM. Ignition is wake-up signal source.

Test Number 7) This step checks BCM for crank signal. If 12 volts are on terminal 1C9 (crank circuit), BCM goes down and brings CPS down with it.

Chart A-1: Flow Chart Central Power Supply (CPS) Check (CRT Equipped). Scheme 216

CHART B, COLOR CRT BLANK WITH IGNITION ON (CRT EQUIPPED)

Note. Test numbers refer to numbers on diagnostic chart.

Test Number 1) This step checks power supply to CPS and CRTC.

Test Number 2) This step determines if CRT/CRTC system is awake and operating.

Test Number 3) This step checks voltage on data line from CRTC to CRT. Normal voltage is between 1.5 and 4.5 volts with minor fluctuations.

Test Number 4) This step checks if CRT or CRTC are causing the low voltage reading on data line.

Chart B: Circuit Diagram (CRT Equipped). Scheme 217

Chart B: Flow Chart Color CRT Blank W/Ignition On (CRT Equipped). Scheme 218

CHART C, COLOR CRT UNABLE TO CONTROL ECCP (CRT EQUIPPED)

IPC indicates loss of serial data communication by displaying the message ELECTRICAL PROBLEM. All other segments are blank. If display is fully illuminated and ELECTRICAL PROBLEM message is displayed, enter diagnostics and proceed to appropriate code chart. Do not use CHART A. Loss of serial data communications can occur for the following reasons

1. Short to ground anywhere in circuit No. 800.
2. Short to voltage anywhere in circuit No. 800.
3. Two opens in circuit No. 800.
4. Loss of 7 volt supply which powers serial communication.
5. Internal BCM or IPC fault.

Note. Test numbers refer to numbers on diagnostic chart. Test Number 1) If climate control page is accessible, CRTC is receiving ignition power and should be capable of communicating with BCM. Test Number 2) This step checks to see if CRTC has lost communication with BCM. Test Number 3) This step checks to see if IPC has lost communication with BCM also. Test Number 4) This step checks continuity of the data line (circuit No. 800). Since data line is a loop, resistance around it should be close to zero ohms. Test Number 5) This step checks for short to ground on data line. Test Number 6) This step checks voltage on data line under normal operating conditions. Normal data line voltage is between 1 and 5 volts and continually fluctuating. Voltage above 5 volts or non-fluctuating voltage indicates a problem in data line causing entire communications network to be inoperative.

Chart C: Circuit Diagram (CRT Equipped). Scheme 219

Chart C: Flow Chart Color CRT Unable to Control ECCP (CRT Equipped). Scheme 220

CHART D, SERIAL DATA CIRCUIT OPEN (CRT EQUIPPED)

Serial data line is redundant at most of the devices it communicates with. Only one line need be connected to each device for that system to function. When making repairs both lines should be made operational. If when ALDL cover is removed the system shuts down, a single open existed before. Now a second open in circuit is being created by removing ALDL cover.

Note. Test numbers refer to numbers on diagnostic chart.

Test Number 1) This test and all subsequent tests are designed to subdivide data line. This is necessary to pinpoint location of open in data line. This is not the only way to pinpoint an open, but in this case, will most quickly lead to the open.

Chart D: Flow Chart Serial Data Circuit Open (CRT Equipped). Scheme 221

CHART D-1, GROUNDED SERIAL DATA CIRCUIT (CRT EQUIPPED)

With grounded serial data circuit, BCM will not be able to communicate with any other devices in system. Voltage measured anywhere in circuit will zero. IPC display will show ELECTRICAL PROBLEM, CRT will display normally and HVAC controls will not function.

Note. Test numbers refer to numbers on diagnostic chart.

Test Number 1) This step splits the system in half to help isolate source of grounded serial data line. If taking ECM out of the system allows both halves of serial data line to rise above one volt, source of short has been located.

Test Number 2) The remaining steps follow same pattern in that components are removed from serial data line until normal voltage range is again measured. When section of circuit is isolated, a simple check of wire for short to ground will differentiate between grounded wire or ground in a device remote.

Chart D-1: Flow Chart Serial Data Circuit (CRT Equipped). Scheme 222

CHART D-2, SERIAL DATA CIRCUIT SHORTED TO VOLTAGE (CRT EQUIPPED)

With a shorted serial data circuit, BCM will not be able to communicate with other devices in system. Voltage measured anywhere in circuit will be above 5 volts. IPC display showing only ELECTRICAL PROBLEM.

Note. Test numbers refer to numbers on diagnostic chart.

Test Number 1) This step splits system in half to help isolate the source of short in the serial data line. If taking ECM out of system allows both halves of serial data line to fall below 5 volts, source of short was in ECM.

Test Number 2) The remaining steps follow the same pattern in that components are removed from serial data line until normal voltage range is again measured.

Chart D-2: Flow Chart Serial Data Circuit Shorted to Voltage (CRT Equipped). Scheme 223

Chart E: Circuit Diagram (CRT Equipped). Scheme 224

Chart E: Flow Chart Color CRT Abnormalities (CRT Equipped). Scheme 225

CODE B110, OUTSIDE TEMP SENSOR CIRCUIT

The outside air temperature sensor is a thermistor that controls signal voltage to BCM. The BCM applies and monitors voltage on circuit No. 735 to sensor. When sensor is cold, its resistance is high, therefore BCM will see a high monitored 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 ignition is on and signal voltage indicates less than -36°F (-38°C), which is open circuit voltage or greater than 131°F (55°C), which is shorted circuit voltage. During time failure is present, a substitute temperature reading will be used to allow continued operation of the climate control system, and continuous compressor at idle will be disabled. The outside air temperature reading BD26 display will indicate the actual sensor reading.

Note. Test numbers refer to numbers on diagnostic chart.

Test Number 1) 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.

Test Number 2) By applying a ground to various points in the circuits, an open can be isolated by observing whether parameter display can be changed from open reading to shorted reading.

Test Number 3) Checks to see if shorted circuit reading is due to circuit or sensor. If shorted circuit reading changes to an open circuit reading after disconnecting sensor, BCM and wiring are okay.

Note On Intermittents

If ambient temperature drops to less than about -36°F (-38°C), this code should be ignored. If B110 is set with any of the following codes: B119, B120, B122, B132 or B440, the most likely cause is an intermittent open circuit No. 736.

If an intermittent Code B110 is being set, manipulate related wiring while observing BD26 display. If failure is induced, reading will jump from its normal value to a reading outside the range of -36°F (-38°C) to 131°F (55°C).

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

Code B110: Circuit Diagram. Scheme 226

Code B110: Flow Chart Outside Temp Sensor Circuit. Scheme 227

CODE B111, A/C HIGH SIDE TEMP SENSOR CIRCUIT

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

Code B111 will set if ignition is on, outside temperature sensor has not failed and reads greater than 32°F (0°C), and signal voltage indicates less than -30°C, which is open circuit voltage or greater than 184°C, which is shorted circuit voltage. During time failure is present, a substitute temperature reading will be used to allow continued operation of climate control system. The A/C high side temperature reading BD27 display will indicate actual sensor reading.

Note. Test numbers refer to numbers on diagnostic chart.

Test Number 1) 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 terminal, BCM and wiring are okay.

Test Number 2) 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.

Test Number 3) Checks to see if shorted circuit reading is due to circuit or sensor. If shorted circuit reading changes to an open circuit reading after disconnecting sensor, BCM and wiring are okay.

If an intermittent Code B111 is being set, check Code B111 snap data value for high side temperature, BD27 display. If BD27 display value is less than -30°C, code was caused by an open in circuit No. 732, circuit No. 736 or high side temperature sensor. If BD27 display is greater than 184°C, code resulted from a short to ground on circuit No. 732 or a shorted high side temperature sensor. Manipulate related wiring while observing BD27 display. If failure is induced, reading will jump from its normal value to a reading outside the range of -30°C to 184°C.

If value displayed by BD27 display is not reasonably close to corresponding gauge pressure reading, check for poor terminal contact or replace sensor.

Code B111: Flow Chart A/C High Side Temp Sensor Circuit. Scheme 228

CODE B112, A/C LOW SIDE TEMP SENSOR CIRCUIT

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

Code B112 will set if ignition is on, outside temperature sensor has not failed and reads greater than 32°F (0°C), and signal voltage indicates less than -29°F (-34°C), which is open circuit voltage or greater than 201°F (94°C), which is shorted circuit voltage. During time failure is present, a substitute temperature reading (same value as outside air temperature) will be used to allow continued operation of climate control system and compressor clutch will be disabled. The A/C low side temperature reading BD28 display will display actual sensor reading.

Note. Test numbers refer to numbers on diagnostic chart.

Test Number 1) 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.

Test Number 2) 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.

Test Number 3) Checks to see if shorted circuit reading is due to circuit or sensor. If shorted circuit reading changes to an open circuit reading after disconnecting sensor, BCM and wiring are okay.

If an intermittent Code B112 is being set, manipulate related wiring while observing BD28 display. If failure is induced, reading will jump from its normal value to a reading outside the range of -34°F (-29°C) to 201°F (94°C).

If value indicated by BD28 display is not reasonably close to corresponding gauge pressure reading, check for poor terminal contact or replace sensor.

Code B112: Flow Chart A/C Low Side Temp Sensor Circuit. Scheme 229

CODE B113, IN-CAR TEMP SENSOR CIRCUIT

The in-car temperature sensor is a thermistor that controls signal voltage to BCM. The BCM applies and monitors voltage on circuit No. 734 to sensor. When sensor is cold, its resistance is high; therefore, BCM will see a high monitored voltage. As sensor warms, its resistance becomes less and monitored 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 has not failed and reads greater than 32°F (0°C), and signal voltage indicates less than -29°F (-34°C), which is open circuit voltage or greater than 206°F (97°C), which is shorted circuit voltage. During time failure is present, a substitute temperature reading will be used to allow continued operation of climate control system. The in-car temperature reading BD25 display will indicate actual sensor reading.

Note. Test numbers refer to numbers on diagnostic chart.

Test Number 1) 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.

Test Number 2) 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.

Test Number 3) Checks to see if shorted circuit reading is due to circuit or sensor. If shorted circuit reading changes to an open circuit reading after disconnecting sensor, BCM and wiring are okay.

If an intermittent Code B113 is being set, manipulate related wiring while observing BD25 display. If failure is induced, reading will jump from its normal value to a reading outside the range of -29°F (-34°C) to 209°F (85°C).

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

Code B113: Flow Chart In-Car Temp Sensor Circuit. Scheme 230

CODE B115, SUN LOAD SENSOR CIRCUIT

The sun load sensor is a thermistor that controls signal voltage to BCM. The BCM applies and monitors voltage on circuit No. 590 to sensor. When sensor is cold, its resistance is high; therefore, BCM will see a high monitored voltage. As sensor warms, its resistance becomes less and monitored voltage is pulled low through sensor ground, circuit No. 736. This monitored voltage will vary between 5 volts (open circuit) and zero volts (shorted circuit). Code B115 will set if ignition is on, outside temperature sensor has not failed and reads greater than 32°F (0°C), and signal voltage indicates less than -29°F (-34°C), which is open circuit voltage, or greater than 201°F (94°C), which is shorted circuit voltage. During time failure is present, a substitute temperature reading will be used to allow continued operation of climate control system. The sun load temperature reading BD32 display will indicate actual sensor reading.

Note. Test numbers refer to numbers on diagnostic chart.

Test Number 1) 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.

Test Number 2) 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.

Test Number 3) Checks to see if shorted circuit reading is due to circuit or sensor. If shorted circuit reading changes to an open circuit reading after disconnecting sensor, BCM and wiring are okay.

If an intermittent Code B115 is being set, check B115 snap data value for sun load temperature, BD32 display. If the BD32 display value is less than -35°C, code resulted from an open in circuit No. 590, circuit No. 736 or sun load temperature sensor. If BD32 display value is greater than 94°C, code resulted from a short to ground on circuit No. 590 or shorted sun load temperature sensor. Manipulate related wiring while observing BD32 display. If failure is induced, reading will jump from its normal value to a reading outside the range of -29°F (-34°C) to 201°F (94°C).

If value displayed by BD32 display is not reasonably close to a corresponding thermometer reading, check for poor terminal contact or replace sensor.

Code B115: Flow Chart Sun Load Sensor Circuit. Scheme 231

CODE B119, TWILIGHT PHOTOCELL CIRCUIT

Note. Ensure nothing is covering sensor before following this procedure.

The twilight sensor uses a photocell to control signal voltage to BCM. The BCM applies and monitors voltage on circuit No. 278 to sensor. When sensor detects darkness, its resistance is high; therefore, BCM will see a high monitored voltage. As sensor detects light, its resistance becomes less and monitored voltage is pulled low through ground circuit No. 736. This signal voltage will vary between 5 volts (open circuit) and zero volts (shorted circuit).

Code B119 will set if ignition is on and signal voltage indicates more than 97 percent, open circuit voltage or less than 2 percent, which is shorted circuit voltage). During time failure is present, a substitute light reading (indicating darkness) will be used to allow continued operation of headlights. The measure of light reading, BD44 display, will indicate actual sensor reading.

Note. Test numbers refer to numbers on diagnostic chart.

Test Number 1) Checks to see if open circuit 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.

Test Number 2) 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.

Test Number 3) Checks to see if shorted circuit reading is due to circuit or sensor. If shorted circuit reading changes to an open circuit reading after disconnecting sensor, BCM and wiring are okay.

If an intermittent Code B119 is being set, manipulate related wiring while observing BD44 display. If failure is induced, reading will jump from its normal value to a reading outside the range of 3-97 percent. Make certain owner is aware not to cover sensor.

Code B119: Circuit Diagram. Scheme 232

Code B119: Flow Chart Twight Photocell Circuit. Scheme 233

CODE B120, TWILIGHT DELAY POTENTIOMETER CIRCUIT

The twilight sentinel uses a potentiometer to indicate desired time delay to BCM. The BCM supplies 5 volts on circuit No. 705 and ground on circuit No. 736 to resistor in left switch assembly. The delay wiper provides variable voltage signal to BCM on circuit No. 271. When slider is moved toward maximum position (maximum delay), resistance is low, therefore BCM will see a high signal voltage. As slider is moved toward minimum position (minimum delay), its resistance increases and signal voltage decreases. This signal voltage will vary between zero volts (open or grounded circuit) and 5 volts (shorted to voltage circuit).

Code B120 will set if ignition is on and signal voltage indicates less than 2 percent (open or grounded circuit) or greater than 98 percent (shorted to voltage). During time failure is present, a substitute delay time (minimum delay) will be implemented, allowing continued operation of twilight system. The reading from potentiometer BD43 display will indicate actual reading.

Note. Test numbers refer to numbers on diagnostic chart.

Test Number 1) Checks to see if open or grounded circuit reading is due to circuit or switch assembly. If open or grounded circuit reading changes to short to voltage reading after jumpering switch assembly terminals, BCM and wiring are okay.

Test Number 2) Measuring voltage between circuit No. 705 and circuit No. 271 checks to see if circuit No 271 is open or shorted to ground.

Test Number 3) Checks to see if short to voltage circuit reading is due to the circuit or switch assembly. If short to voltage reading changes to an open circuit after disconnecting switch, BCM and wiring are okay.

If an intermittent Code B120 is being set, check B120 snap data value for twilight delay BD43 display. If BD43 display value is greater than 98 percent, code resulted from an open in circuit No. 271, circuit No. 736 or left switch pod. If BD43 display value is less than 2 percent, code resulted from a short in left switch pod. Manipulate related wiring while observing BCM data parameter BD43 display. If failure is induced, reading will jump from its normal value to a reading outside range of 2-98 percent.

Code B120: Flow Chart Twight Delay Potentiometer Circuit (1 of 2). Scheme 234

CODES B120 & B122 TWILIGHT DELAY & PANEL DIMMING SIMULTANEOUSLY

Since both potentiometers use same power and ground, problem is in power or ground circuit when both codes B120 and B122 are stored.

Note. Test numbers refer to numbers on diagnostic chart.

Test Number 1) Checks to see if open or grounded circuit reading is due to circuit or switch. If voltage can be read across circuits No. 705 and 736 after disconnecting switch assembly, BCM and wiring are okay.

Test Number 2) Check for 5 volt reference at switch. If 5 volts is present, circuit No. 736 is open. If circuit No. 736 is open, open will be between terminal No. A3 on left switch and cavity G3 on dash-IP transition connector.

Test Number 3) If circuit No. 705 is suspected of being grounded, remove HVAC programmer and BCM connectors prior to making ground check.

Test Number 4) If there is no ground in circuit No. 705 replace HVAC programmer or BCM.

If an intermittent Code B120 and B122 are being set, check B120 snap data value for twilight delay BD43 display. If BD43 display value is greater than 98 percent, code resulted from an open in circuit No. 736 or left switch pod. If BD43 display value is less than 2 percent, code resulted from an open in circuit No. 705 or short in left switch pod. Manipulate related wiring while observing BD43 display. If failure is induced, reading will jump from its normal value to a reading outside the range of 2-98 percent.

Code B120 & 122: Flow Chart Twight Delay & Panel Dimming Simultaneously (2 of 2). Scheme 235

CODE B121, TWILIGHT ENABLE SWITCH CIRCUIT

The twilight enable switch uses the same physical control as delay pot. Inside left switch assembly, enable switch contacts close as soon as time delay slider is moved off of its extreme minimum (off) position. The BCM supplies a voltage on circuit No. 304 to switch. When slider is moved from off position, switch contacts close and signal voltage is pulled low through ground circuit No. 804.

Code B121 will set if vehicle is equipped with twilight sentinel, twilight delay pot has not failed (Code B120), and signal voltage is high when delay slider is greater than 2 seconds (twilight sentinel on), or signal voltage is low when delay slider is less than 3 seconds (twilight sentinel off). During time failure is present, twilight sentinel will operate based on delay input. Whenever delay is greater than 2 seconds, BCM will assume twilight sentinel is on.

Note. Test numbers refer to numbers on diagnostic chart.

Test Number 1) BI82 displays voltage state of circuit at BCM. These conditions can be observed in BI82 display as readings of HI or LO when slider is moved.

Test Number 2) Checks to see if HI reading is due to circuit or switch assembly. If display changes from HI to LO after jumping switch assembly terminals, BCM and wiring are okay.

Test Number 3) Checks to see if LO reading is due to circuit or switch assembly. If display changes from LO to HI when switch assembly is disconnected, both BCM and wiring are okay.

If an intermittent Code B121 is being set, manipulate related wiring. When BCM BI82 displays change-of-state, an "X" will be indicated. Check circuit for an intermittent open or short.

Code B121: Flow Chart Twight Enable Switch Circuit. Scheme 236

CODE B122, PANEL DIMMING POTENTIOMETER CIRCUIT

The panel dimmer is a potentiometer that indicates desired display intensity to BCM. The BCM supplies voltage on circuit No. 705 and a ground on circuit No. 736 to potentiometer in left switch assembly. The wiper provides voltage signal to BCM on circuit No. 686, indicating position of slider and delay time. When slider is moved toward minimum position, its resistance increases and signal voltage decreases.

Code B122 will set if signal voltage indicates less than 2 percent (open or grounded circuit), or greater than 98 percent (shorted to voltage). During time failure is present, a substitute delay time will be implemented to allow continued operation of interior lighting. The reading from potentiometer BD42 display will indicate actual reading.

Note. Test numbers refer to numbers on diagnostic chart.

Test Number 1) Checks to see if open or grounded circuit reading is due to circuits or switch assembly. If open or grounded circuit reading changes to a short to voltage reading, after jumpering switch assembly terminals, BCM and wiring are okay.

Test Number 2) Measuring voltage between circuit No. 705 (5 volts) and circuit No. 686 will determine if circuit No. 686 is open or shorted to ground.

Test Number 3) Checks to see if short to voltage circuit reading is due to 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 an intermittent Code B122 is being set, check B122 snap data value for twilight delay BD42 display. If BD42 display value is greater than 98 percent, code resulted from an open in circuit No. 271, circuit No. 736 or left switch pod. If BD42 display value is less than 2 percent, code resulted from a short in left switch pod. Manipulate related wiring while observing BD42 display. If failure is induced, reading will jump from its normal value to a reading outside the range of 2-98 percent.

Code B122: Flow Chart Panel Dimming Potentiometer Circuit. Scheme 237

CODE B123, PANEL LAMP SWITCH CIRCUIT

Inside left switch assembly, panel lamp switch contacts close when dimming slider is moved to its extreme maximum position. The BCM supplies a voltage on circuit No. 685 to switch. When signal is pulled to ground, BCM turns courtesy light on.

Code B123 will set if panel dimming pot has not failed and BCM sees circuit No. 685 grounded while dimmer switch position was less than a value for maximum panel light brightness. A grounded circuit No. 685 will not only set Code B123, but will also turn courtesy lights on at all times and drain battery.

Note. Test numbers refer to numbers on diagnostic chart.

Test Number 1) BI01 display, dimmer switch input, will read LO if dimming slider is at maximum up position. BI01 display will read HI if dimming slider is not at maximum position.

Test Number 2) By removing switch assembly, a shorted switch can be detected by observing BI01 display.

Test Number 3) By removing BCM connector, short to ground can be isolated as being wire or BCM.

If circuit No. 685 was intermittently grounded, Code B123 could be stored. Manipulate circuit No. 685 while observing BI01 display with dimmer at a low setting. If short occurs, value will switch from HI to LO.

Also check BD42 display. Cycle panel dimming control from minimum to maximum. If BD42 display does not range between 2-98 percent, or never reads more than 75 percent, replace left switch assembly.

Code B123: Flow Chart Panel Lamp Switch Circuit. Scheme 238

CODE B124, VEHICLE SPEED SENSOR (VSS) CIRCUIT PROBLEM

The vehicle speed sensor uses a Permanent Magnet (PM) generator to generate an electrical signal representative of vehicle speed. This signal is sent to ECM through circuit No. 400 (VSS high) and circuit No. 401 (VSS low), where ECM buffers and amplifies signal. Output voltage of generator can be read by using a digital voltmeter on 2-volt AC scale while rotating generator drive (front wheels).

Code B124 will set if following conditions are present for 30 seconds

1. Ignition on
2. No Code B334
3. Transaxle in 4th gear
4. Vehicle speed is zero
5. Engine RPM greater than 1300
6. Condition occurs for at least 2 seconds

Or if following conditions exist

1. Ignition on
2. No Code B334
3. Vehicle speed is zero
4. Code B124 currently set

During time failure is present, cruise control and continuous compressor at idle will be disabled. Vehicle speed reading BD60 display will indicate actual sensor reading.

Note. Test numbers refer to numbers on diagnostic chart.

Test Number 1) Since ECM amplifies and buffers speed signal before it is sent to BCM, Code EO24 in ECM may set along with Code B124 in BCM. If Code B124 sets with a Code EO24, refer to diagnosis for Code EO24.

Test Number 2) Since Code EO24 is not set, problem is not actual sensor. Problem must be with ECM, BCM or dedicated speed data line circuit No. 437 between ECM and BCM.

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

Code B124: Circuit Diagram & Flow Chart VSS Circuit Problem. Scheme 239

CODE B127, GEAR SELECTOR SWITCH CIRCUIT

The gear selector switch (or PRNDD21) is mounted on transaxle assembly. It is a multi-signal switch sending information relative to gear selector position to BCM and ECM. The PRNDD21 switch assembly also contains neutral safety switch. The PRNDD21 switch uses 4 discrete circuits to pull 4 BCM voltages low in various combinations to indicate each gear range. The voltage level of each of circuits is represented in BD41 display as "0" equals grounded and "1" equals not grounded. The 4 digits displayed represent decoder A, B, C and parity inputs in sequence.

The PRNDD21 switch also provides Park/Neutral inputs to ECM in a similar manner using one discrete input. This can be seen using EI74, where HI or LO represent voltage level of input terminal. Code B127 will set if following conditions occur

1. PRNDD21 switch input indicates Park/Neutral, but ECM input does not.
2. PRNDD21 switch input does not indicate Park/Neutral, but ECM input does.
3. Decoder and parity inputs do not agree with possible combinations per BD41 display value chart found in BCM DATA PARAMETERS in introduction portion of this article.

If Code B127 is set, Driver Information Center (DIC) will display warning message GEAR SELECT FAULT and IPC PRNDD21 display will flash.

Note. Test numbers refer to numbers on diagnostic chart.

Test Number 1) Checks BCM inputs when only decoder A and parity circuit are pulled low.

Test Number 2) Checks BCM inputs when only decoder B and C inputs are pulled low. This will complete HI/LO check of all 4 BCM inputs.

Test Number 3) This step is to check gear selector switch problem in other gear ranges.

Test Number 4) Checks to see if code is due to discrepancy between ECM and BCM inputs.

Test Number 5) Checks for short to ground in gear selector switch to BCM circuits.

Test Number 6) Checks for open in circuits to BCM.

Test Number 7) Circuit shorted to ground will result in a "0" for that circuit.

Test Number 8) Checks for open PRNDD21 sensor ground.

Test Number 9) Circuit with open will result in a "1" for that circuit.

Test Number 10) The snap data value of BD41 display will be value that BCM recognized when code was set. This is used to determine whether this value is valid. If it is a valid value, ECM Park/Neutral input must be incorrect to set code.

Test Number 11) If snap value of BD41 display is invalid, it should be determined which of digits are invalid. If all digits read "1", PRNDD21 ground is open. If only one digit is incorrect, that circuit, either in switch or harness, was shorted or open when code was set.

Manipulate related ECM and BCM wiring in each gear range while looking for a change in BD41 or ED74 display values to check for intermittent open or short to ground. Also check terminals for good contact at ECM, BCM and PRNDD21 switch. If good contact exists and Code B127 continues to set, replace PRNDD21 switch.

Code B127: Circuit Diagram. Scheme 240

Code B127: Flow Chart Gear Selector Switch Circuit (1 of 3). Scheme 241

Code B127: Flow Chart Gear Selector Switch Circuit (2 of 3). Scheme 242

Code B127: Flow Chart Gear Selector Switch Circuit (3 of 3). Scheme 243

CODE B132, ENGINE OIL PRESSURE SENSOR CIRCUIT FAULTY

The oil pressure indicator is a variable resistor used to indicate oil pressure to BCM. The BCM supplies voltage on circuit No. 313 to sensor. When the engine is not running (oil pressure low), sensor resistance is low. When the engine is running (increased oil pressure), sensor resistance becomes high. The signal voltage will vary between 5 volts (open circuit) and zero volts (short circuit). Code 132 will set if engine is running and the signal voltage indicates greater than 80 psi for at least 2 seconds. As actual engine oil pressure will never be that high, code indicates an open circuit, faulty sensor or faulty BCM.

Note. Test numbers refer to numbers on diagnostic chart.

Test Number 1) 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.

Test Number 2) By applying a ground to various points in the circuits, an open can be isolated by observing whether the parameter display changes to a short circuit reading.

If an intermittent Code B132 is being set, manipulate the related wiring while observing BCM data parameter BD71. If the failure is induced, the reading will change to a high oil pressure.

Code B132: Ckt Diagram & Flow Chart Eng Oil Pressure Sens Ckt Faulty. Scheme 244

CODE B140, PHONE SYSTEM FAULT

The BCM receives phone status information directly from the phone transceiver on circuit No. 902 and from CRT controller across serial data line. The phone status input to BCM is a pulse width modulated signal that indicates what state the phone is in. The phone status input from the CRT controller is a discrete indication of whether CRT is able to communicate with the phone transceiver across E & C data line.

Code B140 will set if either of the following sets of conditions are met for more than 2 seconds

1. Code B335 is not set
2. CRT controller indicates a phone communication failure

Code B140 will also set if phone status input, BD45 is 7, indicating zero percent pulse width signal (a ground).

Note. For diagnosis of Code B140 cellular telephone will require servicing.

Code B140: Circuit Diagram Phone System Fault. Scheme 245

Circuit Diagram Serial Data Circuit Multiple Intermittent Data Codes. Scheme 246

Flow Chart Serial Data Circuit, Multiple Intermittent Data Codes. Scheme 247

CODE B332, LOSS OF COMPASS DATA

Code B332 will set if communication between the compass and BCM is lost. If Code B332 is set, an ELECTRICAL PROBLEM message will be displayed and the compass will display the last direction indicated until compass communication resumes.

Note. Test numbers refer to numbers on diagnostic chart.

Test Number 1) Checks to see if other data line components are experiencing communications problems.

Test Number 2) Checks status of data line at compass module. Normal data line voltage is between .1 and 4.5 volts.

If an intermittent Code B332 is stored, manipulate the related wiring at compass module and up to splice. An ELECTRICAL PROBLEM message indicates a loss of data and may help locate fault.

Code B332: Flow Chart Loss of Compass Data. Scheme 248

CODE B333, LOSS OF SIR DATA

Code B333 will set if communication between DERM (SIR controller) and BCM is lost. If code B333 is set, ELECTRICAL PROBLEM and INFLATABLE RESTRAINT telltales will be lit.

Note. Test numbers refer to numbers on diagnostic chart.

Test Number 1) Checks to see if other data line components are experiencing communications problems.

Test Number 2) Checks status of data line at compass module. Normal data line voltage is between .1 and 4.5 volts.

If an intermittent code B333 is being stored, manipulate related wiring at DERM. An ELECTRICAL PROBLEM message indicates a loss of data and may help locate fault.

Code B333: Flow Chart Loss of SIR Data. Scheme 249

CODE B334, LOSS OF ECM DATA

Code B334 will set if communication between ECM and BCM is lost. If the BCM remains powered and only serial communication is lost, the vehicle will still run, with ignition key on (engine not running), a LOW OIL PRESSURE message will be displayed followed by an ELECTRICAL PROBLEM message about 25 seconds later.

Note. Test numbers refer to numbers on diagnostic chart.

Test Number 1) If the ECM loses power or ground, code will set since ECM cannot communicate. It is important to note that engine will not start.

Test Number 2) Since prior checks eliminated an open circuit, fault is poor terminal contact at ECM terminal "A8", a faulty CALPAK connection or a faulty ECM.

If an intermittent Code B334 is being set, manipulate the related wiring at ECM. With the ignition key on (engine not running), a LOW OIL PRESSURE message will indicate loss of ECM communication, and possibly help to isolate the intermittent without having to look for the code. Also check ECM and CALPAK connections.

Code B334: Flow Chart Loss of ECM Data. Scheme 250

CODE B335, LOSS OF ECC OR CRTC SERIAL DATA

This code can only be viewed as a history code, because if it was current, service diagnostics could not be entered. Most likely the ECC controls for heating and A/C will also be inoperative when the loss of serial data occurs. Since the serial data lines are redundant, a double open in the circuit No. 800 has to occur to set this code. However, the code will also set for a single open in the power or ground supply to the ECC.

Code B335: Connector Identification Loss of ECC Or CRTC Serial Data. Scheme 251

CODE B336, LOSS OF IPC SERIAL DATA

This code can only be viewed as a history code because if it was current, service diagnostics could not be entered. Since serial data (7 volts) and ground terminals are redundant, it would take a double open in any of those circuits to set the code. A single intermittent open in circuit No. 343 would also set the code.

If codes are intermittent, careful checking of all terminal contacts is required prior to any parts being replaced.

Code B336: Connector Identification Loss of IPC Serial Data. Scheme 252

CODE B337, LOSS OF HVAC PROGRAMMER DATA

Code B337 will set if communication between the programmer and BCM is lost. This can occur if the HVAC loses ignition, ground or both serial data circuits.

Note. Test numbers refer to numbers on diagnostic chart.

Test Number 1) Checks for power and ground up to the programmer. The test light should be on when connected from ignition source to both grounds.

Test Number 2) Since power and ground are available to the programmer, the source for failure is either a double open in the circuit No. 800 or faulty terminal contacts.

Code B337: Flow Chart Loss of HVAC Programmer Data. Scheme 253

CODE B410, CHARGING SYSTEM CIRCUIT FAULT

The generator on this vehicle has fault detection capability built into the regulator. The BCM supplies 12 volts on circuit No. 25 and monitors the field voltage on circuit No. 23.

Code B410 will set if the following conditions exist

1. Engine running
2. Generator enable line is low

Or if the following conditions exist

1. Engine running
2. Generator enable line high
3. Generator field input is less than 2 percent

Or if the following conditions exist

1. Ignition on, engine not running
2. Generator enable line is high

Or if the following conditions exist

1. Ignition on, engine not running
2. Generator enable line is low
3. Generator field input is less than 2 percent

Code B410 will cause the GENERATOR PROBLEM message to be displayed on the DIC and the NO CHARGE telltale to light on the IPC.

Note. Test numbers refer to numbers on diagnostic chart.

Test Number 1) BI51 displays generator signal voltage as HI or LO, depending on the voltage state at BCM. Normally, with key on and engine off, circuit No. 25 voltage will be pulled low by the generator and BI51 will read LO.

Test Number 2) Checks to see if low reading is due to circuit No. 25 or the generator. If display reading changes from LO to HI when the generator is disconnected with engine running, BCM and circuit No. 25 are okay.

Test Number 3) Checks to see if fault is due to BCM or circuit No. 25.

Test Number 4) BD51 displays the amount of generator field activity. Under normal conditions, a reading less than 7 percent would indicate a fault in field circuit at BCM.

Test Number 5) Removing the generator connector will determine if fault is due to generator or an open in circuit No. 25, including BCM and interface connector.

If an intermittent condition exists, check B410 snap data parameters BD61 and BI51. Also check for the following conditions

1. If BD61 is under 500 RPM and BI51 is high, check for an intermittent open in circuit No. 25.
2. If BD61 is under 500 RPM and BI51 is low, check for an intermittent short to ground in circuit No. 23.
3. If BD61 is over 500 RPM and BI51 is high, check for an intermittent short to ground in circuit No. 23.
4. If BD61 is over 500 RPM and BI51 is low, check for an intermittent short to ground in circuit No. 25.

Also perform the battery and charging system checks, to ensure proper operation of these components.

Code B410: Circuit Diagram. Scheme 254

Code B410: Flow Chart Charging System Circuit Fault. Scheme 255

CODE B411 OR B412 BATTERY VOLTAGE TOO HIGH OR TOO LOW

The BCM monitors ignition 1 voltage on terminal No. 3C11 as a reference for fuel control. Code B411 will set when ignition is on, engine RPM is greater than 800 and the BCM sees an ignition 1 reference voltage of less than 10.6 volts. Code B412 will be set if the BCM sees voltage over 16 volts. Both B411 and B412 will cause the GENERATOR PROBLEM message to be displayed on the IPC.

Note. Test numbers refer to numbers on diagnostic chart.

Test Number 1) BD50 displays battery voltage. The normal range is 10.6-16 volts.

Test Number 2) Checks to see if low voltage reading is due to circuit or battery. With engine running, if voltage is less than 10 volts, BCM and wiring are okay.

Test Number 3) Checks to see if low voltage reading is due to circuit or BCM. If voltage reading at BCM is less than 10.6 volts, BCM is okay.

Test Number 4) Checks to see if high voltage reading is due to generator or faulty BCM.

Test Number 5) Checks to see if charging voltage goes too high with higher engine RPM or electrical load.

If an intermittent Code B411 or B412 is being set, observe BD50 display. This battery voltage reading is monitored from 15-amp ISO IGN 1 fuse, fuel reference voltage. If code is being set due to a high current draw in a certain vehicle component, this can be observed by reading BD50 display. Operate various components while watching for reading to drop to less than 10 volts or increase to greater than 16 volts.

Code B411 or B412: Circuit Diagram. Scheme 256

Code B411 or B412: Flow Chart Battery Voltage Too High or Too Low. Scheme 257

CODE B420, RELAY CIRCUITS

BCM operates twilight, courtesy light and fog light relays by providing a ground for relay coils. When relay(s) are on, BCM output will be low and when relay(s) are off, BCM output will be high. BCM also provides an alternating high/low clock signal to Driver Information System (DIS) switch pod to facilitate communications.

Code B420 will be set if ignition is on and output voltage at BCM is not what has been commanded.

Note. Test numbers refer to numbers on diagnostic chart.

Test Number 1) To determine if courtesy light system has failed.

Test Number 2) To determine if twilight system has failed.

Test Number 3) To determine if fog light system has failed.

Test Number 4) To determine if Driver Information System clock signal has failed.

Code B420: Circuit Diagram. Scheme 258

Code B420: Flow Chart Relay Circuit. Scheme 259

CODE B420 (A), COURTESY LAMP RELAY CIRCUITS

BCM operates courtesy lamp relay by providing ground for relay coil. When relay is on, BCM output will be low and when relay is off, BCM output will be high.

Code B420 will set if ignition is on and output voltage at BCM is not what has been commanded.

Note. Test numbers refer to numbers on diagnostic chart.

Test Number 1) Determines which way system has failed.

Test Number 2) Checks to see if short or ground is due to circuit or BCM.

Test Number 3) Verifies relay signal from BCM.

Test Number 4) Checks to see if open circuit is on power or ground side of relay.

Test Number 5) Checks to see if open circuit is on ground side of relay or in relay.

Code B420 (A): Flow Chart Courtesy Lamp Relay Circuit. Scheme 260

CODE B420 (B), TWILIGHT RELAY CIRCUITS

If headlights and parking lights did not cycle on and off when BO05 was selected, this is the system that set Code B420.

Note. Test numbers refer to numbers on diagnostic chart.

Test Number 1) Checks to see if fault is due to an open circuit or a short to ground in circuit. If headlights are always on, there is a short to ground in control circuit. If headlights never turn on, there is an open in one of the circuits.

Test Number 2) Checks to see if short to ground is due to circuit or BCM.

Test Number 3) Checks to see if open circuit is due to circuit or BCM.

Test Number 4) Checks to see 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 (B): Flow Chart Twilight Relay Circuit. Scheme 261

CODE B420 (C), FOG LIGHT RELAY CIRCUIT

If fog lights did not cycle on and off when BO12 was selected, then this is system that set code B420.

Note. Test numbers refer to numbers on diagnostic chart.

Test Number 1) Checks to see if fault is due to an open circuit or a short to ground in circuit. If fog lights are always on, then there is a short to ground in control circuit and if fog lights never turn on, then there is an open in one of the circuits.

Test Number 2) Isolates BCM from circuit problems.

Test Number 3) Checks to see if open circuit is on power or ground side of relay.

If an intermittent code B320 is being set, manipulate related wiring in output function and watch for relays to cycle.

Code B420 (C): Flow Chart Fog Light Relay Circuit. Scheme 262

CODE B420 (D), DIS CLOCK CIRCUIT

If DIS is not functioning correctly, then this is the system that set code B420.

Note. Test numbers refer to numbers on diagnostic chart.

Test Number 1) Checks to see if fault is due to an open circuit or a short to ground in circuit. If test light is always on, then there is a short to voltage in control circuit. If test light never turns on, then there is an open or short to ground in circuit.

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

Code B420 (D): Flow Chart DIS Clock Circuit. Scheme 263

CODE B440, AIR MIX VALVE (DOOR) CIRCUIT PROBLEM

Code B440 is set by BCM if commanded air mix door position is between 30 percent and 80 percent, but actual air mix door position is not within 2 percent of commanded position for 60 seconds. The BCM commands the programmer to move air mix valve (door) over data circuit No. 800. With ignition on, BCM supplies 5 volts on circuit No. 705 and ground on circuit No. 736. A motor in programmer drives air mix valve (door). The BCM monitors door position through a feedback pot on DC motor which varies between zero and 5 volts depending on air mix door position. If air mix valve (door) feedback indicates it is near hot or cold extreme, code will not set since mix door may be at its limit of travel and not able to reach commanded door position.

Operation of air mix valve (door) can be evaluated in BCM display by actual air mix valve (door) position (BD23 display ACT MIX DR) while changing the programmer number (override BS01 display PROGRAM NO).

Note. Test numbers refer to numbers on diagnostic chart.

Test Number 1) BD23 display indicates actual air mix valve (door) position. The normal range is 1-99 percent. BCM override value BS01 display is for program number.

Test Number 2) Checks to see if fault could be due to 5-volt reference and ground circuit, or sensor circuit.

Test Number 3) Checks to see if fault is due to programmer or sensor circuit.

Test Number 4) Checks to see if fault is due to circuit or BCM.

Test Number 5) This step checks to see if open circuit reading is due to circuit No. 736 or circuit No. 705.

If an intermittent Code B440 is being set, check B440 snap data BD23 display. If it was zero percent, check for an intermittent open in circuit No. 736. If it was 100 percent, check for an intermittent open in circuit No. 733 or circuit No. 705. If it was 1-99 percent, check for binding door movement throughout range of door travel and check for a poor ground circuit No. 803. Manipulate related wiring while observing actual air mix door position (BD23 display) movement. If failure is induced, valve (door) position will either stop or jump to an extreme value (zero to 100 percent). This will assist in isolating location of malfunction.

Exit diagnostics and select Max Heat (90°F) and Max Cool (60°F) using normal HVAC controls, waiting a minimum of 2 minutes in each mode to see if code sets.

Code B440: Circuit Diagram. Scheme 264

Code B440: Flow Chart Air Mix Valve (Door) Circuit Problem. Scheme 265

CODES B446, B447 & B448 REFRIGERANT SYSTEM PROBLEM (1 of 2)

Code B446 will set if the low side temperature drops too quickly during compressor engagement. Code B447 will set if low side temperature drops much too quickly during compressor engagement or the low refrigerant pressure switch opens during compressor engagement. Code B448 will set if the low refrigerant pressure switch remains open for greater than 3 minutes.

Note. Test numbers refer to numbers on diagnostic chart.

Test Number 1) BCM input value BI08 displays voltage state of circuit at BCM.

Test Number 2) Checks to see if open circuit reading is due to circuit or switch.

Test Number 3) Checks to see if fault is on ignition side or BCM side of switch circuit.

Test Number 4) This step checks to see if fault is due to pressure switch or a low refrigerant charge.

It has been determined from previous chart that problem is not in low refrigerant pressure switch circuit.

Code B446, 447 & 448: Circuit Diagram. Scheme 266

Code B446, 447 & 448: Flow Chart Refrigerant Sys Problem (1 of 2). Scheme 267

CODES B446, B447 & B448 (2 of 2)

Note. Test numbers refer to numbers on diagnostic chart.

Test Number 1) This is a test to determine if A/C low refrigerant pressure switch opens while compressor is running. If BI08 display remains high during compressor engagement, then system fault is due to refrigerant.

Test Number 2) This checks if switch is opening due to low refrigerant pressure charge or switch.

If Codes B446 and B447 are both set, check low side temperature sensor and circuitry. If okay, evacuate and recharge system. If Codes B447 and/or B448 are both set, check low refrigerant pressure switch and circuit.

Code B446, 447 & 448: Flow Chart Refrigerant Sys Problem (2 of 2). Scheme 268

CODE B449, HIGH SIDE TEMPERATURE TOO HIGH

Code B449 is designed to disengage A/C compressor clutch in the event the high side refrigerant temperature exceeds 199°F (93°C). The A/C compressor clutch will reactivate once high side temperature falls to less than 199°F (93°C). Possible causes for excessively high A/C head pressures should be checked. Diagnose A/C system for refrigerant system performance.

Code B449: Circuit Diagram. Scheme 269

CODE B450, COOLANT TEMPERATURE TOO HIGH

Code B450 is designed to disengage A/C compressor clutch if engine coolant temperature exceeds 261°F (126°C) and re-engage clutch when coolant temperature falls to less than 248°F (120°C). If Code EO14 is also stored, follow diagnosis for that code first. Engine overheating may accompany this code. If coolant temperature exceeds normal operating range, check for sources of overheating. Carefully check all sources of intermittent engine overheating, such as improper coolant fan operation, faulty belt or tension, low coolant level and restrictions or faulty hoses and/or routing.

CODE B482, ANTI-LOCK PRESSURE PROBLEM

This code indicates that brake pressure switch has indicated a low pressure condition to BCM. If Code B482 is set and braking problems are experienced, diagnose ABS and normal braking system. Code B482 sets whenever circuit No. 933 is pulled low to ground and remains low for 50 seconds. As soon as circuit No. 933 goes low, the Red brake telltale will illuminate. The warning message on the Digital Instrument Cluster (DIC) for low brake pressure will not illuminate until after 50 seconds. The amber ANTI-LOCK telltale in the IPC is controlled only by ABS control unit.

Diagnosis

Enter diagnostics and note status of BI18. If BI18 is high, see NOTE ON INTERMITTENTS. If BI18 is low, disconnect 5-pin hydraulic switch connector at ABS pump. If BI18 remains low, repair short to ground in circuit No. 933. If BI18 changes to high, diagnose ABS and normal braking system.

If this code is set as History and you are not experienced braking problems, look for a short to ground in circuit No. 933. Shorted condition would have to be present for at least 50 seconds.

Code B482: Circuit Diagram. Scheme 270

CODE B552, BCM KEEP ALIVE MEMORY ERROR

Code B552 does not necessarily indicate a fault, but is a normal occurrence anytime battery power or ground to BCM has been interrupted. Code B552 cannot be cleared from memory in the normal manner. Code B552 can only be cleared if it is not current. Under normal conditions, code will become history under the following conditions

1. Ignition in lock position
2. Wait for 5 seconds
3. Ignition key on, re-enter diagnosis

After the above conditions have taken place, code should now be history, and can be cleared in the normal manner. This code could be set if the system voltage drops to less than 8 volts at BCM terminal No. 1C9. Possible causes for this are faulty charging system, starter system, extreme cold weather and jump starting vehicle.

Note. Test numbers refer to numbers on diagnostic chart.

Test Number 1) This step is to change Code B552 from current to history.

Test Number 2) Checks to see if Code B552 was set due to a fault during cranking mode.

Test Number 3) Checks for adequate system voltage at BCM terminal No. 1C10. System voltage must not drop to less than 8 volts during engine cranking. By removing fuel pump fuse, engine will not start and voltage during engine cranking can be observed.

Code B552: Circuit Diagram & Flow Chart BCM Keep Alive Memory Error. Scheme 271

CODE B556, ODOMETER (EE) PROM ERROR

Code B556 indicates that EEPROM, which records elapsed odometer mileage, is not being read by BCM. Usually along with Code 556, ERROR will be displayed in the odometer display. The EEPROM contains specific vehicle information such as vehicle ID number, season odometer mileage and certain vehicle options. Since this information is programmed for the specific vehicle in which it is installed, an EEPROM cannot be transferred from one vehicle to another. Check for proper EEPROM installation. If the EEPROM is properly installed, no bent pins, but Code B556 persists, replace EEPROM. Replacement EEPROMs must be obtained through an authorized Delco Service Center.

Code B556: BCM Assembly. Scheme 272

CODE B660, CRUISE CONTROL NOT IN DRIVE

Code B660 will set if cruise control is engaged and BCM detects that gear selector is in Park, Reverse or Neutral. This is done by the BCM based on ECM's input for Park and Neutral, and through circuit No. 24 feeding directly to BCM for Reverse gear status (HI on circuit No. 24 indicates Reverse). During time failure is present, BCM will disengage cruise control.

This code was designed to prevent cruise control operation when vehicle is not in forward gear. If Code B127 is also set or there is complaint of flashing PRNDD21 display, refer to Code B127 diagnosis first. This code can be set if operator selects Neutral while cruise control is engaged. If operator describes this condition but did not move gear selector out of forward gears, check adjustment of PRNDD21, or for looseness in switch mounting or connections that could cause intermittent signals to BCM. Advise operator that shifting gears with cruise control engaged may cause this code to set.

Code B660: Circuit Diagram Cruise Control Not in Drive. Scheme 273

CODE B663, CRUISE SPEED DIFFERENCE BETWEEN ACTUAL & SET IS TOO LARGE

Code B663 will set and disengage cruise control if actual speed is 30 MPH higher or lower than set speed. This code is used to set upper and lower limits for operation of the cruise control system, and can be set under normal conditions if operator accelerates using accelerator pedal and drives 30 MPH greater than set speed. If operator experiences cruise drop out with this code set but did not accelerate 30 MPH greater than set speed, a mechanical problem is indicated.

Note. Test numbers refer to numbers on diagnostic chart.

Test Number 1) BS05 displays a value representing servo position. The commanded range is normally 0-99 percent. If servo will not go to full stroke, vacuum supply, servo or vacuum brake release circuit is leaking.

Test Number 2) This step checks to see if vacuum leak is due to brake release valve and circuit, or servo and source of vacuum.

Test Number 3) This step checks to see if vacuum leak is due to vacuum source or servo.

Test Number 4) This step checks to see if fault is due to intermittent or slow vacuum leak.

Test Number 5) This step checks to see if fault is servo or brake vacuum release circuit.

If Code B663 is setting intermittently, advise vehicle operator that overrunning the cruise control set speed by more than 30 MPH will cause this code to set. Check vacuum source and brake release vacuum lines for proper connections or slow leaks.

Code B663: Circuit Diagram. Scheme 274

Code B663: Flow Chart Cruise Speed Difference Between Actual & Set is Too Late. Scheme 275

CODE B664, CRUISE - ACCELERATION TOO HIGH

This code will set and disengage the cruise control if vehicle acceleration exceeds a preset rate calibrated in the BCM. This could occur on slippery pavement or for some mechanical problems such as transmission slippage. Under these conditions, this code is normal. It should be cleared and vehicle operator should be advised of this.

CODE B667, SET/COAST OR RESUME/ACCEL CIRCUIT SHORTED

Code B667 is designed to catch shorted set/coast and resume/accel switches. Code will set if any of the following conditions are met

1. Set/coast signal is high within one second of cruise on/off switch activation
2. Resume/accel signal is high within one second of cruise on/off switch activation
3. Set/coast signal is high within one second of ignition keying on
4. Resume/accel signal is high within one second of ignition keying on

If set/coast or resume/accel switches were stuck or their signal wires to BCM were shorted to voltage, vehicle could begin cruise operation. To prevent this, Code B667 will set and disable cruise control. If conditions above are met, cruise control will be disabled until BCM sees a low on both of these circuits.

If an intermittent code B667 is being set, manipulate related wiring while observing BCM inputs BI76 and BI77. If failure is induced reading will jump from low to high with switch off. This code can also be set by operator if cruise on/off switch is turned on, or on/off switch was left on when ignition key is turned on and operator was depressing either set/coast or resume/accel switches.

Code B667: Circuit Diagram. Scheme 276

Code B667: Flow Chart Set/Coast or Resume/Accel Circuit Shorted. Scheme 277

CODE B671, CRUISE SERVO POSITION SENSOR CIRCUIT

Code B671 will set if ignition is on and the servo position sensor signal is less than 3 percent. During time failure is present cruise control will be disengaged.

Note. Test numbers refer to numbers on diagnostic chart.

Test Number 1) BD70 display indicates servo position. Normal range is greater than 3 percent.

Test Number 2) Check to see if fault is due to short or open in feedback circuits. Normal resistance across feedback coil should be 15-30 ohms.

Test Number 3) Checks to see if open circuit is due to servo or circuits.

Test Number 4) Checks to see if problem is intermittent. BD70 display will not go as low or high as BS05 display, because of its mechanical limits of travel. It should never go to less than 3 percent.

If an intermittent Code B671 is being set, manipulate related wiring while observing BD70 display. If failure is induced, reading will jump from its normal value to a reading less than 3 percent.

Code B671: Flow Chart Cruise Servo Position Sensor Circuit. Scheme 278

CODE B672, CRUISE VENT SOLENOID CIRCUIT PROBLEM

The cruise control vent solenoid receives pulsed voltage signals from BCM to control the amount of time solenoid is energized. While time output is HI, solenoid is energized and vacuum is not vented from servo. Code B672 will set if cruise is ON, brake is not depressed and BCM output is HI. Under either of these conditions, BCM will disable cruise control until it sees proper output signals. These determinations are made internal to BCM and may, or may not, affect HI or LO reading displayed during service mode. An output display of LO indicates circuit No. 403 should be de-energized (vent solenoid off) and an output display of HI indicates circuit No. 403 should be energized (vent solenoid on).

Circuit No. 403 will be HI when solenoid is energized, as BCM is providing voltage to vent solenoid which has its own full time ground. Circuit No. 403 will be LO when the solenoid is de-energized, as BCM removes voltage feed to solenoid.

Note. Test numbers refer to numbers on diagnostic chart.

Test Number 1) BO01 cycles vent solenoid.

Test Number 2) Checks to see if fault is due to servo or circuit.

Test Number 3) Checks to see if fault is due to open ground circuit or control circuit, including servo solenoid.

Test Number 4) Checks to see if fault is shorted servo or control circuit.

If an intermittent Code B672 is being set, manipulate related wiring while in BO01 display and listen for solenoid to cycle (or stop cycling). This will have to be done slowly as this function cycles the solenoid on and off every 3 seconds. Ensure intermittent condition can be induced a few times during the on (or HI) output interval.

Code B672: Flow Chart Cruise Vent Solenoid Circuit Problem. Scheme 279

CODE B673, CRUISE VACUUM SOLENOID CIRCUIT PROBLEM

The cruise control vent solenoid receives pulsed voltage signals from BCM to control the amount of time solenoid is energized. While time output is HI, solenoid is energized and vacuum is not vented from in servo. Code B673 will set if cruise is ON, brake is not depressed and BCM output is HI. Under either of these conditions, BCM will disable cruise control until BCM sees proper output signals. These determinations are made internal to BCM and may or may not affect HI or LO reading displayed during service mode. An output display of LO indicates circuit No. 403 should be de-energized (vent solenoid off) and an output display of HI indicates circuit No. 402 should be energized (vent solenoid on).

Circuit No. 402 will be HI when solenoid is energized as BCM is providing voltage to vent solenoid which has its own full time ground. Circuit No. 402 will be LO when the solenoid is de-energized as the BCM removes voltage feed to solenoid.

Note. Test numbers refer to numbers on diagnostic chart.

Test Number 1) BO02 cycles vacuum solenoid.

Test Number 2) Checks to see if fault is due to servo or circuit.

Test Number 3) Checks to see if fault is due to open ground circuit or control circuit, including servo solenoid.

Test Number 4) Checks to see if fault is shorted servo or control circuit. If vacuum solenoid is shorted (less than 25 ohms) BCM replacement will also be necessary.

If an intermittent Code B673 is being set, manipulate related wiring while in BO02 display and listen for solenoid to cycle (or stop cycling). This will have to be done slowly as this function cycles the solenoid on and off every 3 seconds. Be aware that solenoid could be at end of 3 second interval. Ensure intermittent condition can be induced a few times during the on (or HI) output interval.

Code B673: Flow Chart Cruise Vacuum Solenoid Ckt Problem. Scheme 280

CODE C710, CRTC SWITCHING CIRCUIT PROBLEM

Note. Test numbers refer to numbers on diagnostic chart.

Test Number 1) CRT monitor needs communication from the CRTC to initially illuminate. Therefore, if CRT monitor lights initially, it is receiving signals from CRTC.

Test Number 2) If CRT is blank at times and Code C710 is set, monitor is not receiving data intermittently.

Test Number 3) Checks voltage on CRTC to CRT data line. Normal voltage is between 1.5 and 4.5 volts and fluctuates some.

Test Number 4) Checks whether CRT or CRTC are causing low voltage reading on data line.

Check connections at CRT monitor and controller. If both connections are clean and tight, either CRT monitor or controller could be at fault.

Code C710: Circuit Diagram. Scheme 281

Code C710: Flow Chart CRTC Switching Circuit Problem. Scheme 282

LEFT DOOR OPEN MESSAGE

BCM supplies and monitors voltage on circuit 3C12. If voltage is sensed as being low (door ajar), BCM will display LEFT DOOR OPEN message under the following conditions

1. PRNDD21 is okay (no Code B127 set)
2. Engine is running
3. Transmission not in Park or Neutral
4. Left door ajar switch input is low

Or if the following conditions exist

1. LEFT DOOR OPEN message already set
2. Left door ajar switch input is low

Left Door Open Message Circuit Diagram. Scheme 283

Left Door Open Message Flow Chart. Scheme 284

RIGHT DOOR OPEN MESSAGE

BCM supplies and monitors voltage on circuit 3C14. If voltage is sensed as being low (door ajar), BCM will display RIGHT DOOR OPEN message under the following conditions

1. PRNDD21 is okay (no Code B127 set)
2. Engine is running
3. Transmission in Park or Neutral
4. Right door ajar switch input is low
5. Vehicle speed over 5 MPH

Or if the following conditions exist

1. RIGHT DOOR OPEN message already set
2. Right door ajar switch is closed

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

Right Door Open Message Flow Chart. Scheme 285

FUEL LEVEL IS LOW MESSAGE

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

Fuel Level Is Low Message Circuit Diagram. Scheme 286

WASHER FLUID IS LOW MESSAGE

The BCM supplies and monitors voltage at terminal 2A4. When fluid level circuit is open, BCM will sense high voltage. When fluid level circuit is closed (low washer fluid), BCM will sense low voltage and illuminate WASHER FLUID IS LOW message. BCM will illuminate message if low washer fluid exist for at least 15 seconds.

Washer Fluid Is Low Message Circuit Diagram. Scheme 287

SEAT BELT TELLTALE & CHIME

BCM supplies and monitors voltage on circuit 3C15. If voltage is sensed as being low (seat belt unbuckled), BCM will display SEAT BELT message under the following conditions

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

Seat Belt Telltale & Chime Circuit Diagram. Scheme 288

Seat Belt Telltale & Chime Flow Chart. Scheme 289

KEY IN IGNITION WARNING CHIME

The BCM supplies and monitors voltage at terminal 3C13. When ignition switch circuit is closed (ignition key in lock position) voltage is pulled low, BCM will display KEY IN IGNITION message under the following conditions

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

FLASHING OR FULL HOT COOLANT GAUGE & FAST CHIME

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

1. Engine coolant temperature greater than 126°C

Or the following conditions.

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

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

Flashing or Full Hot Coolant Gauge & Fast Chime Circuit Diagram. Scheme 290

HEADLIGHTS ARE ON CHIME

BCM monitors terminal 2B7. When parking light switch is closed, voltage is sensed by BCM through circuit No. 308. When parking light switch is open, zero voltage will be sensed by the BCM. BCM will display HEADLAMPS ARE ON message under the following conditions

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

Headlights Are On Chime Circuit Diagram. Scheme 291

PARK BRAKE ON MESSAGE

The BCM supplies and monitors voltage from parking brake switch at terminal 1C5. When parking brake is pulled, switch is closed (grounded). BCM senses voltage being pulled low and illuminates PARK BRAKE ON message. BCM will display message under the following failure conditions

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

Park Brake On Message Circuit Diagram. Scheme 292

BRAKE FLUID IS LOW MESSAGE

The BCM supplies and monitors voltage from brake fluid level switch at terminal 1C2. When brake fluid level is low (switch closed), BCM senses voltage being pulled low, and will illuminate BRAKE FLUID IS LOW message if condition exists for at least 5 seconds. On vehicles without ABS, a brake fluid pressure switch is also used and functions the same as brake fluid level switch.

Brake Fluid Is Low Message Circuit Diagram. Scheme 293

OIL PRESSURE LOW MESSAGE

Oil pressure sensor is a variable resistor the changes resistance proportional to oil pressure. BCM monitors resistance at terminal 3D9. If oil pressure drops to less than 6 psi, BCM will illuminate LOW OIL PRESSURE message. This will occur after engine has been running for at least 5 seconds and if the following conditions exist

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

Or if the following conditions exist

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

Oil Pressure Low Message Circuit Diagram. Scheme 294

OIL LEVEL IS LOW MESSAGE

The BCM supplies and monitors voltage at terminal 1D1. When oil level switch is closed (normal oil level), BCM will sense low voltage. If oil level switch is open (low oil level), BCM will sense high voltage and illuminate OIL LEVEL IS LOW message. This will occur under the following conditions

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

Oil Level Low Message Circuit Diagram. Scheme 295

HOT - IDLE ENGINE MESSAGE

ECM provides 5 volts to coolant temperature sensor circuit. ECM supplies and internally monitors voltage level of coolant temperature circuit at pin C10. If failure conditions for Flashing Coolant Gauge exists for more than 120 seconds, or calculated coolant temperature reaches 130°C and all other failure conditions have been met, BCM will cause temperature gauge bars to flash and send HOT - IDLE ENGINE message to IPC and activate fast paced chime.

Hot - Idle Engine Message Circuit Diagram. Scheme 296

HOT - STOP ENGINE MESSAGE

ECM provides 5 volts to coolant temperature sensor circuit. ECM supplies and internally monitors voltage level of coolant temperature circuit at pin C10. If failure conditions for Flashing Coolant Gauge exist for more than 240 seconds, or calculated coolant temperature reaches 135°C and all other failure conditions have been met, BCM will cause temperature gauge bars to flash and send HOT - STOP ENGINE message to IPC and activate fast paced chime.

TURN SIGNAL ON MESSAGE

Turn signal flasher is provides voltage through turn signal fuse whenever ignition is on. When turn signal switch closes, flasher alternately opens and closes. BCM monitors circuit No. 16 to determine if turn signal switch is closed and turn signal lights are on. If turn signals are left on for more than a quarter mile, BCM will send TURN SIGNAL ON message to DIC.

Turn Signal On Message Circuit Diagram. Scheme 297

ANTILOCK TELLTALE ON

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

Antilock Telltale On Circuit Diagram. Scheme 298

HEADLAMPS SUGGESTED MESSAGE

BCM monitors headlamp switch, twilight sentinel and photocell then compares various voltage inputs and determines whether or not headlights should be on. If message appears with headlights on, check for possible open in circuit No. 953. If there is no message, check circuit No. 278 for short to ground or circuit No. 953 for short to voltage or a shorted photocell. If message appears in daylight, check circuit No. 278 for open or an open in photocell.

Headlamps Suggested Message Circuit Diagram. Scheme 299