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 P0800 – P0899

• P0800 – Transfer Case Control System (MIL Request)
  • causes: Faulty transfer case control module, wiring or connector issues, mechanical problems in the transfer case.
• P0801 – Reverse Inhibit Control Circuit Malfunction
  • causes: Faulty transmission control module, wiring or connector, internal transmission.
• P0802 – Transmission Control System MIL Request Circuit/Open
  • causes: Faulty transmission control module, wiring or connector.
• P0803 – 1-4 Upshift (Skip Shift) Solenoid Control Circuit Malfunction
  • causes: Faulty upshift solenoid, wiring or connector, transmission control module.
• P0804 – 1-4 Upshift (Skip Shift) Lamp Control Circuit Malfunction
  • causes: Faulty indicator lamp, wiring or connector, transmission control module.
• P0805 – Clutch Position Sensor Circuit Malfunction
  • causes: Faulty clutch position sensor, wiring or connector, transmission control module.
• P0806 – Clutch Position Sensor Circuit Range/Performance
  • causes: Faulty sensor, wiring, transmission control module.
• P0807 – Clutch Position Sensor Circuit Low
  • causes: Short to ground, faulty sensor, wiring.
• P0808 – Clutch Position Sensor Circuit High
  • causes: Short to power, faulty sensor, wiring.
• P0809 – Clutch Position Sensor Circuit Intermittent
  • causes: Faulty sensor, intermittent electrical connections, wiring.

OBD / OBDII DTC P0810 – P0819

• P0810 – Clutch Position Control Error
  • causes: Mechanical failure in the clutch assembly, faulty clutch position sensor, transmission control module.
• P0811 – Excessive Clutch Slippage
  • causes: Worn clutch components, hydraulic in the clutch system, transmission control module.
• P0812 – Reverse Input Circuit
  • causes: Faulty transmission range sensor, wiring or connector, transmission control module.
• P0813 – Reverse Output Circuit
  • causes: Faulty transmission components, wiring or connector, transmission control module.
• P0814 – Transmission Range Display Circuit
  • causes: Faulty transmission range display, wiring or connector, transmission control module problems.
• P0815 – Upshift Switch Circuit
  • causes: Faulty upshift switch, wiring or connector, transmission control module.
• P0816 – Downshift Switch Circuit
  • causes: Faulty downshift switch, wiring or connector, transmission control module.
• P0817 – Starter Disable Circuit
  • causes: Faulty starter disable relay, wiring or connector, security system.
• P0818 – Driveline Disconnect Switch Input Circuit
  • causes: Faulty driveline disconnect switch, wiring or connector, transfer case control module.
• P0819 – Up and Down Shift Switch to Transmission Range Correlation
  • Correlation problem between the up and down shift switch and the transmission range indications.
  • causes: Faulty shift switches, transmission range sensor, wiring or connector problems, transmission control module (TCM).

OBD / OBDII DTC P0820 – P0829

• P0820 – Gear Lever X-Y Position Sensor Circuit
  • causes: Faulty gear position sensor, wiring or connector, TCM or gear selector.
• P0821 – Gear Lever X Position Circuit
  • causes: Same as P0820, but specific to the X-axis of the gear position sensor.
• P0822 – Gear Lever Y Position Circuit
  • causes: Same as P0820, but specific to the Y-axis of the gear position sensor.
• P0823 – Gear Lever X Position Circuit Intermittent
  • causes: Intermittent electrical connections, faulty gear position sensor, wiring.
• P0824 – Gear Lever Y Position Circuit Intermittent
  • causes: Same as P0823, but specific to the Y-axis.
• P0825 – Gear Lever Push-Pull Switch (Shift Anticipate)
  • Problem with the gear lever push-pull switch, also known as shift anticipate switch.
  • causes: Faulty gear lever switch, wiring or connector, TCM.
• P0826 – Up and Down Shift Switch Circuit
  • causes: Faulty shift switches, wiring or connector, TCM.
• P0827 – Up and Down Shift Switch Circuit Low
  • causes: Short to ground, faulty shift switches, wiring.
• P0828 – Up and Down Shift Switch Circuit High
  • causes: Short to power, faulty shift switches, wiring.
• P0829 – 5-6 Shift
  • causes: Internal transmission mechanical faults, faulty shift solenoids, TCM.

OBD / OBDII DTC P0830 – P0839

• P0830 – Clutch Pedal Switch ‘A’ Circuit
  • causes: Faulty clutch pedal switch, wiring or connector, ECM or TCM.
• P0831 – Clutch Pedal Switch ‘A’ Circuit Low
  • causes: Short to ground, faulty clutch pedal switch, wiring.
• P0832 – Clutch Pedal Switch ‘A’ Circuit High
  • causes: Short to power, faulty clutch pedal switch, wiring.
• P0833 – Clutch Pedal Switch ‘B’ Circuit
  • causes: Faulty clutch pedal switch, wiring or connector, ECM or TCM.
• P0834 – Clutch Pedal Switch ‘B’ Circuit Low
  • causes: Short to ground, faulty clutch pedal switch, wiring.
• P0835 – Clutch Pedal Switch ‘B’ Circuit High
  • causes: Short to power, faulty clutch pedal switch, wiring.
• P0836 – Four Wheel Drive (4WD) Switch Circuit
  • causes: Faulty 4WD switch, wiring or connector, transfer case control module.
• P0837 – Four Wheel Drive (4WD) Switch Circuit Range/Performance
  • causes: Faulty 4WD switch, wiring problems, transfer case control module.
• P0838 – Four Wheel Drive (4WD) Switch Circuit Low
  • causes: Short to ground, faulty 4WD switch, wiring or connector.
• P0839 – Four Wheel Drive (4WD) Switch Circuit High
  • causes: Short to power, faulty 4WD switch, wiring or connector.

OBD / OBDII DTC P0840 – P0849

• P0840 – Transmission Fluid Pressure Sensor/Switch ‘A’ Circuit
  • causes: Faulty transmission fluid pressure sensor/switch, wiring or connector, hydraulic problems in the transmission.
• P0841 – Transmission Fluid Pressure Sensor/Switch ‘A’ Circuit Range/Performance
  • causes: Same as P0840.
• P0842 – Transmission Fluid Pressure Sensor/Switch ‘A’ Circuit Low
  • causes: Short to ground, faulty sensor/switch, wiring.
• P0843 – Transmission Fluid Pressure Sensor/Switch ‘A’ Circuit High
  • causes: Short to power, faulty sensor/switch, wiring.
• P0844 – Transmission Fluid Pressure Sensor/Switch ‘A’ Circuit Intermittent
  • causes: Intermittent electrical connections, faulty sensor/switch, wiring.
• P0845 – Transmission Fluid Pressure Sensor/Switch ‘B’ Circuit
  • causes: Same as P0840, but specific to sensor/switch ‘B’.
• P0846 – Transmission Fluid Pressure Sensor/Switch ‘B’ Circuit Range/Performance
  • causes: Same as P0841, but specific to sensor/switch ‘B’.
• P0847 – Transmission Fluid Pressure Sensor/Switch ‘B’ Circuit Low
  • causes: Same as P0842, but specific to sensor/switch ‘B’.
• P0848 – Transmission Fluid Pressure Sensor/Switch ‘B’ Circuit High
  • causes: Same as P0843, but specific to sensor/switch ‘B’.
• P0849 – Transmission Fluid Pressure Sensor/Switch ‘B’ Circuit Intermittent
  • causes: Same as P0844, but specific to sensor/switch ‘B’.

OBD / OBDII DTC P0850 – P0859

• P0850 – Park/Neutral Switch Input Circuit
  • causes: Faulty park/neutral switch, wiring or connector, transmission control module.
• P0851 – Park/Neutral Switch Input Circuit Low
  • causes: Short to ground, faulty switch, wiring.
• P0852 – Park/Neutral Switch Input Circuit High
  • causes: Short to power, faulty switch, wiring.
• P0853 – Drive Switch Input Circuit
  • causes: Faulty drive switch, wiring or connector, transmission control module.
• P0854 – Drive Switch Input Circuit Low
  • causes: Short to ground, faulty switch, wiring.
• P0855 – Drive Switch Input Circuit High
  • causes: Short to power, faulty switch, wiring.
• P0856 – Traction Control Input Signal
  • causes: Faulty traction control switch, wiring or connector, traction control system.
• P0857 – Traction Control Input Signal Range/Performance
  • causes: Faulty traction control system, sensor, wiring or connector.
• P0858 – Traction Control Input Signal Low
  • causes: Short to ground, faulty sensors or switches, wiring.
• P0859 – Traction Control Input Signal High
  • causes: Short to power, faulty sensors or switches, wiring.

OBD / OBDII DTC P0860 – P0869

• P0860 – Gear Shift Module Communication Circuit
  • causes: Faulty gear shift module, wiring or connector, CAN bus.
• P0861 – Gear Shift Module Communication Circuit Low
  • causes: Short to ground, faulty gear shift module, wiring.
• P0862 – Gear Shift Module Communication Circuit High
  • causes: Short to power, faulty gear shift module, wiring.
• P0863 – TCM Communication Circuit
  • causes: Faulty TCM, wiring or connector, CAN bus communication.
• P0864 – TCM Communication Circuit Range/Performance
  • causes: Same as P0863.
• P0865 – TCM Communication Circuit Low
  • causes: Short to ground, faulty TCM, wiring.
• P0866 – TCM Communication Circuit High
  • causes: Short to power, faulty TCM, wiring.
• P0867 – Transmission Fluid Pressure
  • causes: Transmission fluid, faulty pressure sensors or solenoids, hydraulic problems within the transmission.
• P0868 – Transmission Fluid Pressure Low
  • causes: Low transmission fluid level, faulty pressure sensors or solenoids, hydraulic problems.
• P0869 – Transmission Fluid Pressure High
  • causes: Blocked fluid passages, faulty pressure sensors or solenoids, transmission mechanical.

OBD / OBDII DTC P0870 – P0879

• P0870 – Transmission Fluid Pressure Sensor/Switch ‘C’ Circuit
  • causes: Faulty sensor/switch, wiring or connector, hydraulic problems in transmission.
• P0871 – Transmission Fluid Pressure Sensor/Switch ‘C’ Circuit Range/Performance
  • causes: Same as P0870.
• P0872 – Transmission Fluid Pressure Sensor/Switch ‘C’ Circuit Low
  • causes: Short to ground, faulty sensor/switch, wiring.
• P0873 – Transmission Fluid Pressure Sensor/Switch ‘C’ Circuit High
  • causes: Short to power, faulty sensor/switch, wiring.
• P0874 – Transmission Fluid Pressure Sensor/Switch ‘C’ Circuit Intermittent
  • causes: Intermittent electrical connections, faulty sensor/switch, wiring.
• P0875 – Transmission Fluid Pressure Sensor/Switch ‘D’ Circuit
  • causes: Same as P0870, but specific to sensor/switch ‘D’.
• P0876 – Transmission Fluid Pressure Sensor/Switch ‘D’ Circuit Range/Performance
  • causes: Same as P0870, but specific to sensor/switch ‘D’.
• P0877 – Transmission Fluid Pressure Sensor/Switch ‘D’ Circuit Low
  • causes: Short to ground, faulty sensor/switch, wiring.
• P0878 – Transmission Fluid Pressure Sensor/Switch ‘D’ Circuit High
  • causes: Short to power, faulty sensor/switch, wiring.
• P0879 – Transmission Fluid Pressure Sensor/Switch ‘D’ Circuit Intermittent
  • causes: Intermittent electrical connections, faulty sensor/switch, wiring.

OBD / OBDII DTC P0880 – P0889

• P0880 – TCM Power Input Signal
  • causes: Faulty TCM, wiring or connector, power supply.
• P0881 – TCM Power Input Signal Range/Performance
  • causes: Same as P0880.
• P0882 – TCM Power Input Signal Low
  • causes: Short to ground, faulty TCM, wiring.
• P0883 – TCM Power Input Signal High
  • causes: Short to power, faulty TCM, wiring.
• P0884 – TCM Power Input Signal Intermittent
  • causes: Intermittent electrical connections, TCM, wiring.
• P0885 – TCM Power Relay Control Circuit/Open
  • causes: Faulty TCM power relay, wiring or connector, TCM.
• P0886 – TCM Power Relay Control Circuit Low
  • causes: Short to ground, TCM power relay, wiring.
• P0887 – TCM Power Relay Control Circuit High
  • causes: Short to power, TCM power relay, wiring.
• P0888 – TCM Power Relay Sense Circuit
  • causes: Faulty TCM power relay, wiring or connector, TCM.
• P0889 – TCM Power Relay Sense Circuit Range/Performance
  • causes: Same as P0888.

OBD / OBDII DTC P0890 – P0899

• P0890 – TCM Power Relay Sense Circuit Low
  • causes: Short to ground, faulty TCM power relay, wiring.
• P0891 – TCM Power Relay Sense Circuit High
  • causes: Short to power, faulty TCM power relay, wiring.
• P0892 – TCM Power Relay Sense Circuit Intermittent
  • causes: Intermittent electrical connections, faulty TCM power relay, wiring.
• P0893 – Multiple Gears Engaged
  • causes: Internal transmission mechanical, solenoids or valves, TCM.
• P0894 – Transmission Component Slipping
  • causes: Worn clutches or bands, hydraulic problems, transmission fluid.
• P0895 – Shift Time Too Short
  • causes: Transmission fluid problems, faulty solenoids, internal transmission mechanical, TCM.
• P0896 – Shift Time Too Long
  • causes: Transmission fluid (e.g., low level or dirty fluid), shift solenoids, internal transmission mechanical problems, TCM.
• P0897 – Transmission Fluid Deteriorated
  • causes: Old or contaminated transmission fluid, lack of regular maintenance, internal transmission wear.
• P0898 – Transmission Control System MIL Request Circuit Low
  • Low signal in the circuit requesting the malfunction indicator lamp (MIL) to illuminate for a transmission control system issue.
  • causes: Short to ground, faulty wiring or connectors, transmission control module (TCM) problems.
• P0899 – Transmission Control System MIL Request Circuit High
  • High signal in the circuit requesting the malfunction indicator lamp (MIL) to illuminate for a transmission control system issue.
  • causes: Short to power, faulty wiring or connectors, transmission control module (TCM) problems.

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.