Common OBD error codes and what they mean for your car.

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Will Kerr

Error codes are designed to let you know when there’s something wrong with you car. Which is great – but only if you know what they mean. So let’s get into it.

What are OBD error codes?

When something’s up with your car, you’ll usually see warning lights on your dashboard. But these won’t give you the exact nature of the problem. To get a more detailed understanding of the issue you need the ODB code (also known as a DTC or Diagnostic Trouble Code).

To get this five digit code from your car, you’ll need a piece of kit called an ODB scanner. Unless, of course, you’re with By Miles and have a Miles Tracker installed. If you do, you can simply pop into our app and use the Car Medic feature to scan for error codes. ‘Appy days!


Understanding ODB codes. 

As mentioned, these codes always have five characters. The first is a letters, followed by 4 numbers. Running through these one by one will help you narrow down the problem. 

The first character.

This gives you the general area where the issue lies: 

P: Powertrain system. 

B: Body.

C: Chassis. 

U: Network communications. 

The second character.

This will tell you if the code is generic (something that could apply in almost any car) or manufacturer specific. 

Generic codes are:

P0, P2, P34-P39, B0, B3, C0, C3, U0, and U3, 

Manufacturer specific codes are:

 P1, P30-P33, B1, B2, C1, C2, U1, and U2.

The third character.

This will tell you the system that’s having trouble: 

1: Fuel or air metering.

2: Fuel or air metering injection.

3: Ignition.

4: Emissions.

5: Speed and idle control.

6: Computer output circuit.

7, 8, 9: Transmission.

The final two characters.

These will give you the particular problem. You might find what they mean in the common codes below. If not, you can look up the code from an online directory of OBD codes

Some common OBD error codes.

Check engine light: P0101, P0420, P0171.

The ‘check engine’ light can come on for all sorts of reasons. Some of the most common error codes you’ll get for engine trouble include P0101 (Mass or Volume Air Flow Circuit Range/Performance Problem), P0420 (Catalyst System Efficiency Below Threshold), and P0171 (System Too Lean Bank 1).

These error codes often point to problems with the engine’s fuel and emissions systems, such as a faulty oxygen sensor, a malfunctioning catalytic converter, or a vacuum leak. If these codes come up, you’ll want a mechanic’s help as a high priority.

engine trouble

ABS warning light: C1234, C0110, U0121.

The ABS (Anti-Lock Braking System) warning light is another one commonly seen flashing on the dash. Error codes associated with the ABS warning light include C1234 (Speed Wheel Rear Left Input Signal Missing), C0110 (Pump Motor Circuit Malfunction), and U0121 (Lost Communication With Anti-Lock Brake System Control Module). 

These error codes can mean problems with wheel speed sensors, the ABS pump motor, or communication issues between your ABS and other systems. Again, these should be looked at urgently. 

Airbag warning light:  B0011, B0021, B0081.

Common error codes you might find when the airbag warning light comes on include B0011 (Driver Frontal Deployment Loop Stage 1 Open), B0021 (Driver Side Deployment Loop Resistance High), and B0081 (Passenger Presence System Performance). 

These codes can mean problems with airbag sensors, deployment loops, or passenger presence sensors. It goes without saying you want your airbags to be working, so it’s important to act if these come up.

Transmission warning light: P0700, P0715, P0760.

If the transmission warning light is on, the codes you’re most likely to find include P0700 (Transmission Control System Malfunction), P0715 (Input/Turbine Speed Sensor Circuit Malfunction), and P0760 (Shift Solenoid C Malfunction). 

These error codes may indicate problems with transmission sensors, solenoids, or control modules. To keep your gears happy, be sure to get the problem looked at. 

Fuel system warning light: P0180, P0193, P0455.

The fuel system warning light indicates issues with the vehicle’s fuel system, which is responsible for storing, delivering, and regulating fuel for the engine. Common error codes associated with the fuel system warning light include P0180 (Fuel Temperature Sensor A Circuit Malfunction). 

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