The Diagnostic Trouble Code system is a huge help to the home mechanic. That's because the car will be able to tell you what’s wrong through 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 denotes what part of the car is at fault.
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 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
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
| 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) |
