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Decoding OBD-II Diagnostic Trouble Codes

What are… Diagnostic Trouble Codes

Modern cars (made from 1996 onward) are very clever, and will actually be able to tell you what’s wrong if they have a problem, thanks to the OBD-II system. If the car's computer ever encounters a problem, a fault code or Diagnostic Trouble Code (DTC), will be stored within the car’s ECU memory. With a scanner plugged into the car’s On-Board Diagnostics (OBD) port you can read the list of codes stored, and therefore find out what the problem is.

The codes follow a formula making it easy to generally know what the issue is before even looking at the chart below.

The First Letter…

The first letter denotes what part of the car is at fault.

P = Powertrain

B = Body

C = Chassis

U = Network

The First Number…

The first of the four numbers will be either a ‘0’ or a ‘1’.

0 = Standardized (SAE) fault codes

1 = Manufacturer specific codes

The Second Number…

The second digit denotes which of the car systems is at fault. There are eight different categories;

0 = Fuel and Air Metering and Auxiliary Emission Controls

1 = Fuel and Air Metering

2 = Fuel and Air Metering (injector circuit)

3 = Ignition systems or misfires

4 = Auxiliary emission controls

5 = Vehicle speed control & idle control systems

6 = Computer & output circuit

7 = Transmission

The Third And Fourth Numbers…

The third and fourth digits are simply used to define the exact fault code in question.

In our example we can see that the DTC is P0303.

P = Powertrain fault

0 = Standardized fault

3 = Ignition systems or misfire

03 – misfire on cylinder 3

What are… Diagnostic Trouble Codes

OBD II trouble code chart*

Code Code Identification
P0101 Mass air flow (MAF) sensor circuit, range or performance problem
P0102 Mass air flow (MAF) sensor circuit, low input
P0103 Mass air flow (MAF) sensor circuit, high input
P0106 Manifold absolute pressure (MAP) sensor circuit, range or performance problem
P0107 Manifold absolute pressure (MAP) sensor circuit, low input
P0108 Manifold absolute pressure (MAP) sensor circuit, high input
P0112 Intake air temperature (IAT) circuit, low input
P0113 Intake air temperature (IAT) circuit, high input
P0117 Engine coolant temperature (ECT) circuit, low input
P0118 Engine coolant temperature (ECT) circuit, high input
P0121 Throttle position sensor (TPS) circuit, range or performance problem
P0122 Throttle position sensor (TPS) circuit, low input
P0123 Throttle position sensor (TPS) circuit, high input
P0125 Insufficient coolant temperature for closed loop fuel control
P0131 Oxygen sensor circuit, low voltage (pre-converter sensor, left bank)
P0132 Oxygen sensor circuit, high voltage (pre-converter sensor, left bank)
P0133 Oxygen sensor circuit, slow response (pre-converter sensor, left bank)
P0134 Oxygen sensor circuit - no activity detected (pre-converter sensor, left bank)
P0135 Oxygen sensor heater circuit malfunction (pre-converter sensor, left bank)
P0137 Oxygen sensor circuit, low voltage (post-converter sensor, left bank)
P0138 Oxygen sensor circuit, high voltage (post-converter sensor, left bank)
P0140 Oxygen sensor circuit - no activity detected (post-converter sensor, left bank)
P0141 Oxygen sensor heater circuit malfunction (post-converter sensor, left bank)
P0143 Oxygen sensor circuit, low voltage (#2 post-converter sensor, left bank)
P0144 Oxygen sensor circuit, high voltage (#2 post-converter sensor, left bank)
P0146 Oxygen sensor circuit - no activity detected (#2 post-converter sensor, left bank)
P0147 Oxygen sensor heater circuit malfunction (#2 post-converter sensor, left bank)
P0151 Oxygen sensor circuit, low voltage (pre-converter sensor, right bank)
P0152 Oxygen sensor circuit, high voltage (pre-converter sensor, right bank)
P0153 Oxygen sensor circuit, slow response (pre-converter sensor, right bank)
P0154 Oxygen sensor circuit - no activity detected (pre-converter sensor, right bank)
P0155 Oxygen sensor heater circuit malfunction (pre-converter sensor, right bank)
P0157 Oxygen sensor circuit, low voltage (post-converter sensor, right bank)
P0158 Oxygen sensor circuit, high voltage (post-converter sensor, right bank)
P0160 Oxygen sensor circuit - no activity detected (post-converter sensor, right bank)
P0161 Oxygen sensor heater circuit malfunction (post-converter sensor, right bank)
P0171 System too lean, left bank
P0172 System too rich, left bank
P0174 System too lean, right bank
P0175 System too rich, right bank
P0300 Engine misfire detected
P0301 Cylinder number 1 misfire detected
P0302 Cylinder number 2 misfire detected
P0303 Cylinder number 3 misfire detected
P0304 Cylinder number 4 misfire detected
P0305 Cylinder number 5 misfire detected
P0306 Cylinder number 6 misfire detected
P0307 Cylinder number 7 misfire detected
P0308 Cylinder number 8 misfire detected
P0325 Knock sensor circuit malfunction
P0327 Knock sensor circuit, low output
P0336 Crankshaft position sensor circuit, range or performance problem
P0337 Crankshaft position sensor, low output
P0338 Crankshaft position sensor, high output
P0339 Crankshaft position sensor, circuit intermittent
P0340 Camshaft position sensor circuit
P0341 Camshaft position sensor circuit, range or performance problem
P0401 Exhaust gas recirculation, insufficient flow detected
P0404 Exhaust gas recirculation circuit, range or performance problem
P0405 Exhaust gas recirculation sensor circuit low
P0410 Secondary air injection system
P0418 Secondary air injection pump relay control circuit
P0420 Catalyst system efficiency below threshold, left bank
P0430 Catalyst system efficiency below threshold, right bank
P0440 Evaporative emission control system malfunction
P0441 Evaporative emission control system, purge control circuit malfunction
P0442 Evaporative emission control system, small leak detected
P0446 Evaporative emission control system, vent system performance
P0452 Evaporative emission control system, pressure sensor low input
P0453 Evaporative emission control system, pressure sensor high input
P0461 Fuel level sensor circuit, range or performance problem
P0462 Fuel level sensor circuit, low input
P0463 Fuel level sensor circuit, high input
P0500 Vehicle speed sensor circuit
P0506 Idle control system, rpm lower than expected
P0507 Idle control system, rpm higher than expected
P0601 Powertrain Control Module, memory error
P0602 Powertrain Control module, programming error
P0603 Powertrain Control Module, memory reset error
P0604 Powertrain Control Module, memory error (RAM)
P0605

Powertrain Control Module, memory error (ROM)

 Not all codes apply to all models