Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
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HOMESERVICE MANUALSCADILLAC1991SEVILLE STSREPAIR AND DIAGNOSIS (SINGLE PAGE)ENGINE PERFORMANCESYSTEMENGINE CONTROLS - TESTS W/CODES
1991 Cadillac Seville STS
Engine Controls - Tests W/Codes
1991 Cadillac Seville STSSECTION Engine Controls - Tests W/Codes
- Introduction
- Self-Diagnostic System
- Entering Self-Diagnostics
- Displaying Trouble Codes
- BCM & Pcm Trouble Code Identification
- Operation Of Service Mode
- Diagnostic Parameters
- Specific Test Type Availability
- BCM Specific Data (BD) Tests
- BD20: Commanded Blower Voltage
- BD21: Coolant Temperature
- BD22: Commanded Air-Mix Door
- BD23: Actual Air-Mix Door Position
- BD24: Air Delivery Mode
- BD25: In-Car Temperature
- BD26: Actual Outside Air Temperature
- BD27: High Side Temperature Condenser Out
- BD28: Low Side Temperature (Evaporator In)
- BD32: Sun Load Temperature
- BD40: Actual Fuel Level
- BD42: Dimming Pot
- BD43: Twilight Delay Pot
- BD44: Twilight Photocell
- BD50: Battery Charge
- BD51: Alternator Field
- BD60: Vehicle Speed
- BD61: Engine Speed
- BD90: Option 1 EEPROM
- BD91: Option 2 EEPROM
- BD98: Ignition Cycle Counter
- BD99: BCM Prom Id
- BCM Specific Input (Bi) Tests
- Bi01: Courtesy Light Panel Switch
- Bi02: Parking Light Switch
- Bi03: Driver Front Door Ajar Switch
- Bi04: Passenger's Rear Door Ajar Switch
- Bi05: Door Jamb Switch
- Bi06: Door Handle Switch
- Bi07: Trunk Open Switch
- Bi08: A/C Low Refrigerant Pressure Switch
- Bi09: Windshield Washer Fluid Level Switch
- Bi30: Temp/Time Switch
- Bi51: Alternator Feedback
- Bi55: CCR Fault Line
- BCM Specific Output (BO) Tests
- BCM Specific Override (BS) Tests
- Pcm Specific Data (Ed) Tests
- Ed01: Throttle Position Sensor (TPS)
- Ed02: Manifold Air Pressure
- Ed03: Computed Barometric Pressure
- Ed04: Coolant Temperature
- Ed05: Manifold Air Temperature (Mat) Sensor
- Ed08: Spark Advance
- Ed10: Battery State Of Charge
- Ed11: Engine Speed
- Ed12: Vehicle Speed
- Ed30: Left Injector Pulse Width
- Ed31: Right Injector Pulse Width
- Ed32: Left Oxygen Sensor Voltage
- Ed33: Right Oxygen Sensor Voltage
- Ed34: Left Oxygen Sensor Cross Counts
- Ed35: Right Oxygen Sensor Cross Counts
- Ed36: Left Fuel Integrator
- Ed37: Right Fuel Integrator
- Ed38: Left Block Learn Display
- Ed39: Right Block Learn Display
- Ed70: Cruise Control Feedback
- Ed71: PRNDL 1 Status
- Ed72: PRNDL 2 Status
- Ed98: Ignition Cycles
- Ed99: Pcm Programmable Read Only Memory (Prom) Id Code
- Pcm Specific Input (EI) Tests
- Pcm Specific Output (EO) Tests
- Pcm Specific Override Tests
- BCM Specific Data (BD) Tests
- IPC System Self-Diagnostics
- Diagnostic Tests
- Self-Diagnostic System Check
- PFI Chart A-1, Inoperative Service Engine Soon Light
- PFI Chart A-2, No Start Or Stall After Start
- PFI Chart A-3, Service Engine Soon On (No Codes Present)
- PFI Chart A-4, Power Balance Test
- PFI Chart A-5, Fuel Pressure & Injector Flow (1 Of 2)
- PFI Chart A-5, Fuel Pressure & Injector Flow (2 Of 2)
- PFI Chart A-6, Oxygen Sensor Test
- PFI Chart A-7, Emissions Performance Test
- PFI Chart C-3, Canister Purge Diagnosis
- PFI Chart C-1, Pcm Replacement Check
- Chart B-1, Odometer Power/Ground Problem
- Chart B-2, BCM-To-IPC Communication Problem
- Chart B-3, CCDIC Problem
- Chart B-4, BCM-To-Cps Power/Ground Problem
- Chart B-5, Vacuum Fluorescent Power Supply Problem
- Chart B-6, IPC-To-Cps Power/Ground Problem
- Chart B-7, BCM-To-Cps Wake-Up Signal Problem
- Chart B-8, Power Loss From Cps To Other Components
- Chart C-1, CCDIC Symptom Diagnosis
- Chart C-2, CCDIC Completely Blank
- Chart C-3, CCDIC Display Reads System Problem
- Chart C-4, CCDIC Display Reads System Problem
- Pcm Chart A, Multiple Codes Stored (Hard)
- Pcm Code EO12, No Distributor (Tach) Signal
- Pcm Code EO13, Right Oxygen Sensor Not Ready
- Pcm Code EO14, Shorted Coolant Sensor Circuit
- Pcm Code EO15, Open Coolant Sensor Circuit
- Pcm Code EO16, Alternator Voltage Out Of Range
- Pcm Code EO17, Left Oxygen Sensor Not Ready
- Pcm Code EO19, Shorted Fuel Pump Circuit
- Pcm Code EO20, Open Fuel Pump Circuit (1 Of 3)
- Pcm Code EO20, Open Fuel Pump Circuit (2 Of 3)
- Pcm Code EO20, Fuel Pump Fuse Blown (3 Of 3)
- Pcm Code EO21, Shorted TPS Circuit (Signal Voltage High)
- Pcm Code EO22, Open TPS Circuit (Signal Voltage Low)
- Pcm Code EO23, Est Circuit Problem (1 Of 2)
- Pcm Code EO23, Est Circuit Problem (2 Of 2)
- Pcm Code EO24, Speed Sensor Circuit Problem
- Pcm Code EO26, Shorted Throttle Switch Circuit
- Pcm Code EO27, Open Throttle Switch Circuit
- Pcm Code EO30, ISC Rpm Out Of Range
- Pcm Code EO31, Shorted Map Sensor Circuit
- Pcm Code EO32, Open Map Sensor Circuit
- Pcm Code EO34, Map Signal Too High
- Pcm Code EO37, Shorted Mat Sensor Circuit
- Pcm Code EO38, Open Mat Sensor Circuit
- Pcm Code EO39, VCC Engagement Problem (1 Of 2)
- Pcm Code EO39, VCC Engagement Problem (2 Of 2)
- Pcm Code EO40, Open PSPS Circuit
- Pcm Code EO41, No Cam Sensor Signal
- Pcm Code EO42, Left O2 Sensor Lean Signal
- Pcm Code EO43, Left O2 Sensor Rich Signal
- Pcm Code EO44, Right O2 Sensor Lean Signal
- Pcm Code EO45, Right O2 Sensor Rich Signal
- Pcm Code EO46, Right To Left Bank Fueling Imbalance
- Pcm Code EO47, BCM-To-Pcm Data Problem
- Pcm Code EO48, EGR System Fault (1 Of 2)
- Pcm Code EO48, EGR System Fault (2 Of 2)
- Pcm Code EO51, Mem-Cal Error
- Pcm Code EO52, Pcm Memory Reset
- Pcm Code EO53, Distributor Signal Interrupt
- Pcm Code EO55, TPS Out Of Adjustment
- Pcm Code EO58, Pass Key Control Problem
- Pcm Code EO60, Cruise Control With Transmission Not In Drive
- Pcm Code EO61, Cruise Control Vent Solenoid Circuit
- Pcm Code EO62, Cruise Control Vacuum Solenoid Circuit
- Pcm Code EO63, Vehicle Speed/Set Speed Difference Too High
- Pcm Code EO64, Acceleration Too High
- Pcm Code EO65, Cruise Control Servo Position Sensor Failure
- Pcm Code EO66, Engine Rpm Too High With Cruise Engaged
- Pcm Code EO67, Set/Coast Or Resume/ACCEL Switch Shorted
- Pcm Code EO68, Cruise Control Command Problem
- Pcm Code EO70, Intermittent TPS Signal
- Pcm Code EO71, Intermittent Map Sensor
- Pcm Code EO73, Intermittent Coolant Sensor Signal
- Pcm Code EO74, Intermittent Mat Sensor Signal
- Pcm Code EO75, VSS Signal Interrupt
- Pcm Code EO80, Fuel System Rich
- Pcm Code EO85, Throttle Body Service Required
- Pcm Code EO90, VCC Brake Switch Input Problem
- Pcm Code EO91, Park/Neutral Switch Problem (1 Of 2)
- Pcm Code EO91, Park/Neutral Switch Problem (2 Of 2)
- Pcm Code EO92, Heated Windshield Request Problem
- Pcm Code EO96, Torque Converter Overstress
- Pcm Code EO97, Park/Neutral To Drive/Reverse At High Throttle Angle
- Pcm Code EO98, Park/Neutral To Drive/Reverse While Outside Of ISC Control Range
- Pcm Code EO99, Cruise Servo Applied Not In Cruise
- BCM Code B110, Outside Air Temperature Sensor Circuit
- BCM Code B111, A/C High Side Temperature Sensor Circuit
- BCM Code B112, A/C Low Side Temperature Sensor Circuit
- BCM Code B113, In-Car Temperature Sensor Circuit
- BCM Code B115, SUNLOAD Temperature Sensor
- BCM Code B119, Twilight Photocell Circuit
- BCM Code B120, Twilight Delay Pot Circuit
- BCM Codes B120 & B122, Twilight Delay & Panel Dimming
- BCM Code B121, Twilight Enable Switch
- BCM Code B122, Panel Light Dimming Pot Circuit
- BCM Code B123, Courtesy Light Switch Circuit
- Multiple Intermittent Codes
- BCM Code B333, Loss Of Sir (DERM) Data
- BCM Code B334, Loss Of Pcm Data
- BCM Code B335, Loss Of CCDIC Data
- BCM Code B336, Loss Of IPC Data
- BCM Code B337, Loss Of A/C-Heater Programmer Data
- BCM Code B410, Charging System Circuit
- BCM Codes B411 & B412, Battery Voltage Low Or High
- BCM Code B420, Relay Circuits (1 Of 5)
- BCM Code B420, Courtesy Light Relay Circuit (2 Of 5)
- BCM Code B420, Twilight Relays Circuit (3 Of 5)
- BCM Code B420, High/Low Beam Relays Circuit (4 Of 5)
- BCM Code B420, Retained Accessory Power Relays Circuit (5 Of 5)
- BCM Code B440, A/C-Heater Air Mix Door Circuit Problem
- BCM Codes B446 & B447, Low Refrigerant Pressure
- BCM Code B448, Low Refrigerant Pressure
- BCM Code B449, A/C-Heater High Side Temperature Too High
- BCM Code B450, HVAC Coolant Temperature Too High
- BCM Code B552, Keep Alive Memory Error
- BCM Code B556, Odometer EEPROM Error
- Summary
RENDER: 1.0x
NO RELATED
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.