Not all OBDII codes cause an engine light, OBD codes or DTC (diagnostic trouble code) are stored by the ECU (Engine Control Unit) or PCM (Powertrain Control Module) to point the mechanic to the cause.  The engine light is an indicator of problems.  The engine light on its own does not provide details, but reading the stored DTC is a good pointer to where the issue is.

If a DTC is stored in your ECU, it doesn’t necessary mean that there will be an engine light.  In fact no other indicator may be present.  The engine light is typically reserved for drivability or emission problems.  If you’re a DIY person, you should invest in a good OBDII scanner, now available with bluetooth.

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OBD / OBDII DTC stored in the ECU (May be causing an engine light):

1. Body Codes (B0XXX – B3XXX)
   • B0100 – B0199: Airbags, Seat Belts
   • B0200 – B0299: Body Control Modules, Windows, Doors

Body Codes B0200 – B0299

• B0200 – Driver/Passenger Seat Occupant Sensor Circuit Open
  • causes: Open circuit, faulty occupant sensor, wiring or connector.
• B0201 – Driver/Passenger Seat Occupant Sensor Circuit Short to Battery
  • causes: Short circuit, faulty occupant sensor, wiring.
• B0202 – Driver/Passenger Seat Occupant Sensor Circuit Short to Ground
  • causes: Short circuit, faulty occupant sensor, wiring.
• B0203 – Driver/Passenger Seat Occupant Sensor Circuit Open/Short to Ground
  • causes: Open circuit, short circuit, faulty occupant sensor, wiring.
• B0204 – Driver/Passenger Seat Occupant Sensor Circuit Short to Voltage
  • causes: Electrical fault, faulty occupant sensor, wiring.
• B0205 – Driver/Passenger Seat Occupant Sensor Circuit Short to Ground/Short to Battery
  • causes: Short circuit, faulty occupant sensor, wiring.
• B0206 – Driver/Passenger Seat Occupant Sensor Circuit Resistance Low
  • causes: Faulty occupant sensor, wiring.
• B0207 – Driver/Passenger Seat Occupant Sensor Circuit Resistance High
  • causes: Faulty occupant sensor, wiring.
• B0208 – Driver/Passenger Seat Occupant Sensor Circuit Resistance Out of Range
  • causes: Faulty occupant sensor, wiring.
• B0209 – Driver/Passenger Seat Occupant Sensor Circuit Performance
  • causes: Faulty occupant sensor, wiring.

OBD / OBDII DTC B0210 – B0219

• B0210 – Driver/Passenger Seat Occupant Sensor Circuit Failure
  • causes: Faulty occupant sensor, wiring or connector.
• B0211 – Driver/Passenger Seat Occupant Sensor Calibration Not Performed
  • causes: Sensor not calibrated, faulty occupant sensor.
• B0212 – Driver/Passenger Seat Occupant Classification System Malfunction
  • causes: Faulty occupant classification system, sensor or control module.
• B0213 – Driver/Passenger Seat Occupant Classification System Performance
  • causes: Faulty occupant classification system, sensor or control module.
• B0214 – Driver/Passenger Seat Occupant Detection Circuit Short to Ground
  • Common causes: Short circuit, faulty occupant detection system, wiring.
• B0215 – Driver/Passenger Seat Occupant Detection Circuit Open
  • Common causes: Open circuit, faulty occupant detection system, wiring or connector.
• B0216 – Driver/Passenger Seat Occupant Detection Circuit Short to Battery
  • causes: Short circuit, faulty occupant detection system, wiring.
• B0217 – Driver/Passenger Seat Occupant Detection Circuit Short to Voltage
  • causes: Electrical fault, faulty occupant detection system, wiring.
• B0218 – Driver/Passenger Seat Occupant Detection Circuit Low
  • causes: Faulty occupant detection system, wiring or connector.
• B0219 – Driver/Passenger Seat Occupant Detection Circuit High
  • causes: Faulty occupant detection system, wiring.

OBD / OBDII DTC B0220 – B0229

• B0220 – Seat Occupant Detection Circuit Performance
  • causes: Faulty occupant detection system, sensor or control module.
• B0221 – Seat Occupant Detection Circuit Failure
  • causes: Faulty occupant detection system, wiring or connector.
• B0222 – Seat Occupant Detection Sensor
  • causes: Faulty occupant detection sensor, wiring or connector.
• B0223 – Seat Occupant Detection Sensor Circuit
  • causes: Faulty occupant detection sensor, wiring or connector.
• B0224 – Seat Occupant Detection Sensor Circuit Open
  • causes: Open circuit, faulty occupant detection sensor, wiring or connector.
• B0225 – Seat Occupant Detection Sensor Circuit Short to Ground
  • causes: Short circuit, faulty occupant detection sensor, wiring.
• B0226 – Seat Occupant Detection Sensor Circuit Short to Battery
  • causes: Short circuit, faulty occupant detection sensor, wiring.
• B0227 – Seat Occupant Detection Sensor Circuit Short to Voltage
  • causes: Electrical fault, faulty occupant detection sensor, wiring.
• B0228 – Seat Occupant Detection Sensor Circuit Low
  • causes: Faulty occupant detection sensor, wiring or connector.
• B0229 – Seat Occupant Detection Sensor Circuit High
  • Common causes: Faulty occupant detection sensor, wiring.

OBD / OBDII DTC B0230 – B0239

• B0230 – Driver/Passenger Seat Occupant Detection Sensor Performance
  • causes: Faulty occupant detection sensor, sensor or control module.
• B0231 – Driver/Passenger Seat Occupant Detection Sensor Failure
  • causes: Faulty occupant detection sensor, wiring or connector.
• B0232 – Airbag Deployment Indication Input Fault
  • causes: Faulty signal from the airbag deployment sensor, wiring or connector.
• B0233 – Airbag Deployment Indication Input Circuit Open
  • causes: Open circuit, wiring or connector.
• B0234 – Airbag Deployment Indication Input Circuit Short to Ground
  • causes: Short circuit, wiring.
• B0235 – Airbag Deployment Indication Input Circuit Short to Battery
  • causes: Short circuit, wiring.
• B0236 – Airbag Deployment Indication Input Circuit Short to Voltage
  • causes: Electrical fault, wiring
• B0237 – Airbag Deployment Indication Input Circuit Low
  • causes: Faulty airbag deployment indicator, wiring or connector.
• B0238 – Airbag Deployment Indication Input Circuit High
  • causes: Faulty airbag deployment indicator, wiring.
• B0239 – HVAC Temperature Sensor #1 (Driver) Circuit Range/Performance
  • causes: Faulty HVAC temperature sensor, wiring or connector.

OBD / OBDII DTC B0240 – B0249

• B0240 – HVAC Temperature Sensor #1 (Driver) Circuit Low
  • causes: Faulty HVAC temperature sensor, short to ground, wiring.
• B0241 – HVAC Temperature Sensor #1 (Driver) Circuit High
  • causes: Faulty HVAC temperature sensor, short to power, wiring.
• B0242 – HVAC Temperature Sensor #2 (Passenger) Circuit Range/Performance
  • causes: Faulty HVAC temperature sensor, wiring or connector.
• B0243 – HVAC Temperature Sensor #2 (Passenger) Circuit Low
  • causes: Faulty HVAC temperature sensor, short to ground, wiring.
• B0244 – HVAC Temperature Sensor #2 (Passenger) Circuit High
  • causes: Faulty HVAC temperature sensor, short to power, wiring.
• B0245 – HVAC Blend Door Actuator Circuit
  • causes: Faulty HVAC blend door actuator, wiring or connector.
• B0246 – HVAC Blend Door Actuator Circuit Range/Performance
  • causes: Faulty HVAC blend door actuator, wiring.
• B0247 – HVAC Blend Door Actuator Circuit Low
  • causes: Faulty HVAC blend door actuator, short to ground, wiring.
• B0248 – HVAC Blend Door Actuator Circuit High
  • causes: Faulty HVAC blend door actuator, short to power, wiring.
• B0249 – HVAC Air Distribution Door Actuator Circuit
  • causes: Faulty HVAC air distribution door actuator, wiring or connector.

OBD / OBDII DTC B0250 – B0259

• B0250 – HVAC Air Distribution Door Actuator Circuit Range/Performance
  • causes: Faulty HVAC air distribution door actuator, wiring.
• B0251 – HVAC Air Distribution Door Actuator Circuit Low
  • causes: Faulty HVAC air distribution door actuator, short to ground, wiring.
• B0252 – HVAC Air Distribution Door Actuator Circuit High
  • causes: Faulty HVAC air distribution door actuator, short to power, wiring.
• B0253 – HVAC Mode Door Actuator Circuit
  • causes: Faulty HVAC mode door actuator, wiring or connector.
• B0254 – HVAC Mode Door Actuator Circuit Range/Performance
  • causes: Faulty HVAC mode door actuator, wiring.
• B0255 – HVAC Mode Door Actuator Circuit Low
  • causes: Faulty HVAC mode door actuator, short to ground, wiring.
• B0256 – HVAC Mode Door Actuator Circuit High
  • causes: Faulty HVAC mode door actuator, short to power, wiring.
• B0257 – HVAC Recirculation Actuator Circuit
  • causes: Faulty HVAC recirculation actuator, wiring or connector.
• B0258 – HVAC Recirculation Actuator Circuit Range/Performance
  • causes: Faulty HVAC recirculation actuator, wiring.
• B0259 – HVAC Recirculation Actuator Circuit Low
  • causes: Faulty HVAC recirculation actuator, short to ground, wiring.

OBD / OBDII DTC B0260 – B0269

• B0260 – HVAC Recirculation Actuator Circuit High
  • causes: Faulty HVAC recirculation actuator, short to power, wiring.
• B0261 – HVAC Air Inlet Door Actuator Circuit
  • causes: Faulty HVAC air inlet door actuator, wiring or connector.
• B0262 – HVAC Air Inlet Door Actuator Circuit Range/Performance
  • causes: Faulty HVAC air inlet door actuator, wiring.
• B0263 – HVAC Air Inlet Door Actuator Circuit Low
  • causes: Faulty HVAC air inlet door actuator, short to ground, wiring.
• B0264 – HVAC Air Inlet Door Actuator Circuit High
  • causes: Faulty HVAC air inlet door actuator, short to power, wiring.
• B0265 – HVAC Air Flow Mode Door Actuator Circuit
  • causes: Faulty HVAC air flow mode door actuator, wiring or connector.
• B0266 – HVAC Air Flow Mode Door Actuator Circuit Range/Performance
  • causes: Faulty HVAC air flow mode door actuator, wiring.
• B0267 – HVAC Air Flow Mode Door Actuator Circuit Low
  • causes: Faulty HVAC air flow mode door actuator, short to ground, wiring.
• B0268 – HVAC Air Flow Mode Door Actuator Circuit High
  • causes: Faulty HVAC air flow mode door actuator, short to power, wiring.
• B0269 – HVAC Air Temperature Internal Sensor Circuit
  • causes: Faulty HVAC air temperature internal sensor, wiring or connector.

OBD / OBDII DTC B0270 – B0279

• B0270 – HVAC Air Temperature Internal Sensor Circuit Range/Performance
  • causes: Faulty HVAC air temperature internal sensor, wiring.
• B0271 – HVAC Air Temperature Internal Sensor Circuit Low
  • causes: Faulty HVAC air temperature internal sensor, short to ground, wiring.
• B0272 – HVAC Air Temperature Internal Sensor Circuit High
  • causes: Faulty HVAC air temperature internal sensor, short to power, wiring.
• B0273 – HVAC Air Temperature External Sensor Circuit
  • causes: Faulty HVAC air temperature external sensor, wiring or connector.
• B0274 – HVAC Air Temperature External Sensor Circuit Range/Performance
  • causes: Faulty HVAC air temperature external sensor, wiring.
• B0275 – HVAC Air Temperature External Sensor Circuit Low
  • causes: Faulty HVAC air temperature external sensor, short to ground, wiring.
• B0276 – HVAC Air Temperature External Sensor Circuit High
  • causes: Faulty HVAC air temperature external sensor, short to power, wiring.
• B0277 – HVAC Air Temperature External Sensor Circuit Open
  • causes: Open circuit, faulty HVAC air temperature external sensor, wiring or connector.
• B0278 – HVAC Mode Door Feedback Circuit Low Voltage
  • causes: Electrical issue, faulty HVAC mode door actuator, wiring.
• B0279 – HVAC Mode Door Feedback Circuit High Voltage
  • causes: Electrical issue, faulty HVAC mode door actuator, wiring.

OBD / OBDII DTC B0280 – B0289

• B0280 – HVAC Mode Door Feedback Circuit Short to Ground
  • causes: Short circuit, faulty HVAC mode door actuator, wiring.
• B0281 – HVAC Mode Door Feedback Circuit Short to Battery
  • causes: Short circuit, faulty HVAC mode door actuator, wiring.
• B0282 – HVAC Mode Door Feedback Circuit Failure
  • causes: Faulty HVAC mode door actuator, wiring or connector.
• B0283 – Rear Defrost Circuit Failure
  • causes: Faulty rear defrost system, wiring or connector, control module.
• B0284 – Rear Defrost Circuit High Voltage
  • causes: Electrical issue, faulty rear defrost system, wiring.
• B0285 – Rear Defrost Circuit Low Voltage
  • causes: Electrical issue, faulty rear defrost system, wiring.
• B0286 – Left Front Turn Signal Circuit
  • causes: Faulty turn signal bulb or assembly, wiring or connector.
• B0287 – Right Front Turn Signal Circuit
  • causes: Faulty turn signal bulb or assembly, wiring or connector.
• B0288 – Turn Signal Switch Circuit Low Voltage
  • causes: Electrical issue, faulty turn signal switch, wiring.
• B0289 – Turn Signal Switch Circuit High Voltage
  • causes: Electrical issue, faulty turn signal switch, wiring.

OBD / OBDII DTC B0290 – B0299+

• B0290 – Lost Communication With Body Control Module “A”
  • causes: Communication issue, faulty body control module, wiring or connector.
• B0291 – Lost Communication With Body Control Module “B”
  • causes: Communication issue, faulty body control module, wiring or connector.
• B0292 – Lost Communication With Body Control Module “C”
  • causes: Communication issue, faulty body control module, wiring or connector.
• B0293 – Door Ajar Lamp Circuit Failure
  • causes: Faulty door ajar switch, wiring or connector, instrument panel.
• B0294 – Door Ajar Lamp Circuit Open
  • causes: Open circuit, faulty door ajar switch, wiring or connector.
• B0295 – Door Ajar Lamp Circuit Short to Ground
  • causes: Short circuit, faulty door ajar switch, wiring.
• B0296 – Door Ajar Lamp Circuit Short to Battery
  • causes: Short circuit, faulty door ajar switch, wiring.
• B0297 – HVAC Control Module Requested MIL Illumination
  • causes: Issues requiring MIL illumination as detected by the HVAC control module, communication problems between modules.
• B0298 – HVAC Control Module
  • causes: Faulty HVAC control module, wiring or connector, software or calibration.
• B0299 – Outside Air Temperature Sensor Circuit Low
  • causes: Faulty outside air temperature sensor, short to ground, wiring or connector.
• B029A – Outside Air Temperature Sensor Circuit High
  • causes: Faulty outside air temperature sensor, short to power, wiring.
• B029B – Outside Air Temperature Sensor Circuit Open
  • causes: Open circuit, faulty outside air temperature sensor, wiring or connector.
• B029C – Outside Air Temperature Sensor Circuit Performance
  • causes: Faulty outside air temperature sensor, sensor or circuit calibration, wiring.
• B029D – Outside Air Temperature Sensor Circuit Failure
  • causes: Faulty outside air temperature sensor, wiring or connector.

Why is my Engine Light on?

On-Board Diagnostic (OBD / OBDII) codes are stored within the Engine Control Unit (ECU) or Powertrain Control Module (PCM). These modules store the codes, monitor and control engine performance and emissions. When the system detects a fault or irregularity, it generates a diagnostic trouble code (DTC), which is stored in the ECU/PCM’s memory. This code can be retrieved using an OBD scanner, providing insights into issues.

What Are These Codes in my ECU?

On-Board Diagnostic (OBD or OBDII ) codes are part of a vehicle’s self-diagnostic system.  The ECU and sensors work together to produce DTCs, sometimes resulting in an engine light.  The codes generated do not always cause an engine light.  The development of OBD systems began in the 1980s, driven by increasing environmental concerns and regulations, especially in California. The California Air Resources Board (CARB) played a key role in this, mandating the first OBD systems.  OBD, introduced in the 1980s, was the first system of its kind.  The evolution of OBD technology culminated in the universal OBDII standard in the mid-1990s.  It provided basic capabilities to monitor and diagnose vehicle functions, primarily for emissions control.  OBDII, introduced in the mid-1990s, is a more advanced and standardized system.  This OBDII advanced system was mandatory for all cars sold in the United States from 1996 onwards.  OBDII offers broader diagnostics, real-time data, and standardization across most vehicles.  This made it easier to diagnose and address issues.  OBDII’s standardized diagnostic trouble codes (DTC) and connector types are much better than the earlier OBD system, making it easier to diagnosis and repair.