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. Powertrain Codes (P0XXX, P2XXX, P34XX – P39XX)
   • P0001 – P0099: Fuel and Air Metering
   • P0100 – P0199: Fuel and Air Metering
   • P0200 – P0299: Fuel and Air Metering (Injector Circuit)
   • P0300 – P0399: Ignition System or Misfire
   • P0400 – P0499: Auxiliary Emissions Controls
   • P0500 – P0599: Vehicle Speed Controls and Idle Control System
   • P0600 – P0699: Computer Output Circuit
   • P0700 – P0799: Transmission
   • P0800 – P0899: Transmission
   • P0900 – P0999: clutch and auxiliary emission control
   • P1XXX: Manufacturer-specific codes

Powertrain Codes P0500 – P0509

• P0500 – Vehicle Speed Sensor ‘A’ Malfunction
  • causes: Faulty vehicle speed sensor, wiring or connector, malfunctioning instrument cluster or ECM.
• P0501 – Vehicle Speed Sensor ‘A’ Range/Performance
  • causes: Faulty sensor, wiring problems, drivetrain.
• P0502 – Vehicle Speed Sensor ‘A’ Circuit Low Input
  • causes: Short to ground, faulty sensor, wiring.
• P0503 – Vehicle Speed Sensor ‘A’ Intermittent/Erratic/High
  • causes: Faulty sensor, intermittent electrical, wiring.
• P0504 – Brake Switch ‘A’/’B’ Correlation
  • Discrepancy between brake ‘A’ and ‘B’.
  • Common causes: Faulty brake light switch, wiring or connector, alignment problem with brake switch.
• P0505 – Idle Control System Malfunction
  • causes: Faulty idle air control valve, vacuum leaks, throttle body.
• P0506 – Idle Control System RPM Lower Than Expected
  • causes: Vacuum leaks, dirty throttle body, faulty idle air control valve.
• P0507 – Idle Control System RPM Higher Than Expected
  • causes: Vacuum leaks, stuck idle air control valve, throttle body.
• P0508 – Idle Air Control System Circuit Low
  • causes: Short to ground, faulty idle air control valve, wiring.
• P0509 – Idle Air Control System Circuit High
  • causes: Short to power, faulty idle air control valve, wiring.
• P0510 – Closed Throttle Position Switch Malfunction
  • causes: Faulty throttle position sensor/switch, wiring or connector, ECM.

OBD / OBDII DTC P0511 – P0519

• P0511 – Idle Air Control Circuit
  • causes: Faulty idle air control valve, wiring or connector, ECM.
• P0512 – Starter Request Circuit
  • causes: Faulty starter relay, ignition switch, wiring or connector.
• P0513 – Incorrect Immobilizer Key
  • causes: Faulty immobilizer system, incorrect or damaged key, ECM/PCM.
• P0514 – Battery Temperature Sensor Circuit Range/Performance
  • causes: Faulty battery temperature sensor, wiring or connector, charging system.
• P0515 – Battery Temperature Sensor Circuit
  • causes: Faulty sensor, wiring or connector.
• P0516 – Battery Temperature Sensor Circuit Low
  • causes: Short to ground, faulty sensor, wiring.
• P0517 – Battery Temperature Sensor Circuit High
  • causes: Short to power, faulty sensor, wiring.
• P0518 – Idle Air Control Circuit Intermittent
  • causes: Faulty idle air control valve, intermittent electrical connections, wiring.
• P0519 – Idle Air Control System Performance
  • causes: Dirty or sticking idle air control valve, vacuum leaks, throttle body.

OBD / OBDII DTC P0520 – P0529

• P0520 – Engine Oil Pressure Sensor/Switch Circuit Malfunction
  • causes: Faulty oil pressure sensor/switch, wiring or connector, mechanical problems affecting oil pressure.
• P0521 – Engine Oil Pressure Sensor/Switch Circuit Range/Performance
  • causes: Faulty sensor/switch, incorrect oil viscosity, mechanical issues affecting oil pressure.
• P0522 – Engine Oil Pressure Sensor/Switch Circuit Low Voltage
  • causes: Short to ground, faulty sensor/switch, wiring.
• P0523 – Engine Oil Pressure Sensor/Switch Circuit High Voltage
  • causes: Short to power, faulty sensor/switch, wiring.
• P0524 – Engine Oil Pressure Too Low
  • causes: Low oil, faulty oil pump, blocked oil filter, internal engine problems.
• P0525 – Cruise Control Servo Control Circuit Range/Performance
  • causes: Faulty cruise control servo, wiring or connector, cruise control system.
• P0526 – Fan Speed Sensor Circuit
  • causes: Faulty fan speed sensor, wiring or connector, fan motor.
• P0527 – Fan Speed Sensor Circuit Range/Performance
  • causes: Same as P0526.
• P0528 – Fan Speed Sensor Circuit No Signal
  • causes: Faulty fan speed sensor, wiring or connector issues, fan motor failure.
• P0529 – Fan Speed Sensor Circuit Intermittent
  • causes: Faulty fan speed sensor, intermittent electrical connections, wiring.

OBD / OBDII DTC P0530 – P0539

• P0530 – A/C Refrigerant Pressure Sensor Circuit Malfunction
  • causes: Faulty A/C refrigerant pressure sensor, wiring or connector, A/C system.
• P0531 – A/C Refrigerant Pressure Sensor Circuit Range/Performance
  • causes: Same as P0530.
• P0532 – A/C Refrigerant Pressure Sensor Circuit Low Input
  • causes: Short to ground, faulty sensor, wiring.
• P0533 – A/C Refrigerant Pressure Sensor Circuit High Input
  • causes: Short to power, faulty sensor, wiring.
• P0534 – Air Conditioner Refrigerant Charge Loss
  • causes: Refrigerant leaks, faulty A/C components, improper refrigerant charge.
• P0535 – A/C Evaporator Temperature Sensor Circuit
  • causes: Faulty A/C evaporator temperature sensor, wiring or connector.
• P0536 – A/C Evaporator Temperature Sensor Circuit Range/Performance
  • Same as P0535.
• P0537 – A/C Evaporator Temperature Sensor Circuit Low Input
  • causes: Short to ground, faulty sensor, wiring.
• P0538 – A/C Evaporator Temperature Sensor Circuit High Input
  • causes: Short to power, faulty sensor, wiring.
• P0539 – A/C Evaporator Temperature Sensor Circuit Intermittent
  • causes: Faulty sensor, intermittent electrical connections, wiring.

OBD / OBDII DTC P0540 – P0549

• P0540 – Intake Air Heater ‘A’ Circuit
  • causes: Faulty intake air heater, wiring or connector, control circuit.
• P0541 – Intake Air Heater ‘A’ Circuit Low
  • causes: Short to ground, faulty intake air heater, wiring.
• P0542 – Intake Air Heater ‘A’ Circuit High
  • causes: Short to power, faulty intake air heater, wiring.
• P0543 – Intake Air Heater ‘A’ Circuit Open
  • causes: Faulty intake air heater, disconnected or broken wiring, connector.
• P0544 – Exhaust Gas Temperature Sensor Circuit (Bank 1 Sensor 1)
  • causes: Faulty exhaust gas temperature sensor, wiring or connector.
• P0545 – Exhaust Gas Temperature Sensor Circuit Low (Bank 1 Sensor 1)
  • causes: Short to ground, faulty sensor, wiring.
• P0546 – Exhaust Gas Temperature Sensor Circuit High (Bank 1 Sensor 1)
  • causes: Short to power, faulty sensor, wiring.
• P0547 – Exhaust Gas Temperature Sensor Circuit (Bank 2 Sensor 1)
  • causes: Same as P0544, but Bank 2, Sensor 1.
• P0548 – Exhaust Gas Temperature Sensor Circuit Low (Bank 2 Sensor 1)
  • causes: Same as P0545, but Bank 2, Sensor 1.
• P0549 – Exhaust Gas Temperature Sensor Circuit High (Bank 2 Sensor 1)
  • causes: Same as P0546, but Bank 2, Sensor 1.

OBD / OBDII DTC P0550 – P0559

• P0550 – Power Steering Pressure Sensor Circuit Malfunction
  • causes: Faulty power steering pressure sensor, wiring or connector.
• P0551 – Power Steering Pressure Sensor Circuit Range/Performance
  • causes: Faulty sensor, wiring, power steering system.
• P0552 – Power Steering Pressure Sensor Circuit Low Input
  • causes: Short to ground, faulty sensor, wiring.
• P0553 – Power Steering Pressure Sensor Circuit High Input
  • causes: Short to power, faulty sensor, wiring.
• P0554 – Power Steering Pressure Sensor Circuit Intermittent
  • causes: Faulty sensor, intermittent electrical connections, wiring.
• P0555 – Brake Booster Pressure Sensor Circuit
  • causes: Faulty brake booster pressure sensor, wiring or connector.
• P0556 – Brake Booster Pressure Sensor Circuit Range/Performance
  • causes: Same as P0555.
• P0557 – Brake Booster Pressure Sensor Circuit Low Input
  • causes: Short to ground, faulty sensor, wiring.
• P0558 – Brake Booster Pressure Sensor Circuit High Input
  • causes: Short to power, faulty sensor, wiring.
• P0559 – Brake Booster Pressure Sensor Circuit Intermittent
  • causes: Faulty sensor, intermittent electrical connections, wiring.

OBD / OBDII DTC P0560 – P0569

• P0560 – System Voltage Malfunction
  • causes: Battery, alternator malfunction, electrical system.
• P0561 – System Voltage Unstable
  • causes: Alternator, poor battery, electrical system.
• P0562 – System Voltage Low
  • causes: Weak or dead battery, faulty alternator, wiring.
• P0563 – System Voltage High
  • causes: Faulty alternator, electrical system, battery.
• P0564 – Cruise Control Multi-Function Input ‘A’ Circuit
  • causes: Faulty cruise control switches, wiring or connector, cruise control module.
• P0565 – Cruise Control On Signal Malfunction
  • causes: Faulty cruise control switches, wiring or connector, control module.
• P0566 – Cruise Control Off Signal Malfunction
  • causes: Same as P0565.
• P0567 – Cruise Control Resume Signal Malfunction
  • causes: Faulty cruise control switches, wiring or connector, control module.
• P0568 – Cruise Control Set Signal Malfunction
  • causes: Same as P0565.
• P0569 – Cruise Control Coast Signal Malfunction
  • causes: Faulty cruise control switches, wiring or connector, control module.

OBD / OBDII DTC P0570 – P0579

• P0570 – Cruise Control Accelerate Signal Malfunction
  • causes: Same as P0565.
• P0571 – Cruise Control/Brake Switch ‘A’ Circuit Malfunction
  • causes: Faulty brake switch, wiring or connector, cruise control system.
• P0572 – Cruise Control/Brake Switch ‘A’ Circuit Low
  • causes: Short to ground, faulty brake switch, wiring.
• P0573 – Cruise Control/Brake Switch ‘A’ Circuit High
  • causes: Short to power, faulty brake switch, wiring.
• P0574 – Cruise Control System – Vehicle Speed Too High
  • causes: Driver error, malfunctioning vehicle speed sensor, cruise control system.
• P0575 – Cruise Control Input Circuit Malfunction
  • causes: Faulty cruise control switches, wiring or connector, control module.
• P0576 – Cruise Control Input Circuit Low
  • causes: Short to ground, faulty switches, wiring.
• P0577 – Cruise Control Input Circuit High
  • causes: Short to power, faulty switches, wiring.
• P0578 – Cruise Control Multi-Function Input ‘A’ Circuit Stuck
  • causes: Faulty cruise control switches, wiring or connector, cruise control module.
• P0579 – Cruise Control Multi-Function Input ‘A’ Circuit Range/Performance
  • causes: Faulty cruise control switches, wiring or connector, control module.

OBD / OBDII DTC P0580 – P0589

• P0580 – Cruise Control Multi-Function Input ‘A’ Circuit Low
  • causes: Short to ground, faulty switches, wiring.
• P0581 – Cruise Control Multi-Function Input ‘A’ Circuit High
  • causes: Short to power, faulty switches, wiring.
• P0582 – Cruise Control Vacuum Control Circuit/Open
  • causes: Faulty vacuum control solenoid, vacuum leaks, wiring or connector.
• P0583 – Cruise Control Vacuum Control Circuit Low
  • causes: Short to ground, faulty vacuum control solenoid, wiring.
• P0584 – Cruise Control Vacuum Control Circuit High
  • causes: Short to power, faulty vacuum control solenoid, wiring.
• P0585 – Cruise Control Switch Malfunction
  • causes: Faulty cruise control switches, wiring or connector, control module.
• P0586 – Cruise Control Vent Solenoid Circuit/Open
  • causes: Faulty vent solenoid, wiring or connector, cruise control system.
• P0587 – Cruise Control Vent Solenoid Circuit Low
  • causes: Short to ground, faulty vent solenoid, wiring.
• P0588 – Cruise Control Vent Solenoid Circuit High
  • causes: Short to power, faulty vent solenoid, wiring.
• P0589 – Cruise Control Multi-Function Input ‘B’ Circuit
  • causes: Faulty cruise control switches, wiring or connector, control module.

OBD / OBDII DTC P0590 – P0599

• P0590 – Cruise Control Multi-Function Input ‘B’ Circuit Stuck
  • causes: Faulty cruise control switches, wiring or connector, control module.
• P0591 – Cruise Control Multi-Function Input ‘B’ Circuit Range/Performance
  • Same as P0589.
• P0592 – Cruise Control Multi-Function Input ‘B’ Circuit Low
  • causes: Short to ground, faulty switches, wiring.
• P0593 – Cruise Control Multi-Function Input ‘B’ Circuit High
  • causes: Short to power, faulty switches, wiring.
• P0594 – Cruise Control Servo Actuator Circuit/Open
  • causes: Faulty cruise control servo, wiring or connector, control module.
• P0595 – Cruise Control Servo Actuator Circuit Low
  • causes: Short to ground, faulty servo, wiring.
• P0596 – Cruise Control Servo Actuator Circuit High
  • causes: Short to power, faulty servo, wiring.
• P0597 – Thermostat Heater Control Circuit/Open
  • causes: Faulty thermostat heater, wiring or connector, control module.
• P0598 – Thermostat Heater Control Circuit Low
  • causes: Short to ground, faulty thermostat heater, wiring.
• P0599 – Thermostat Heater Control Circuit High
  • causes: Short to power, faulty thermostat heater, wiring.

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.

Are These Codes Causing an Engine Light?

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.