Use the car’s OBD reader to identify the engine or fuel fault code, then repair the affected part rather than relying on code clearing. The main engine and fuel faults are misfires, injector problems, incorrect fuel, glow-plug faults, and ECU communication failure. A cleared code can return after a specific distance, and clearing a limp-mode fault while its cause remains can make the engine wear three times faster.
Read the engine and fuel codes
- Right-click the car and open
OBD. Connecting takes about three seconds. - Choose
Diagnosisto view codes. Orange codes are active; grey codes are only stored history; red indicates a critical fault. - Use the reader from outside a stationary car, or as the driver while stopped. A passenger may operate it while the car is moving.
The ECU checks the car approximately once per second. Some faults activate limp mode, which normally limits engine power to 40 percent and turns on the amber CHECK lamp. For the first five seconds after starting, limp mode is temporarily inactive; it returns if the ECU detects the fault again.
Engine and fuel fault codes
| Code | Meaning and effect | Repair |
|---|---|---|
P0300 | Random misfire; engine condition is below 75 percent. Power is limited to the engine’s condition. Below 45 percent, the engine may stutter and stall. | Replace the engine. The engine cannot be repaired; the Keratatek additive only helps protect against future wear. |
P0301-P0308 | Misfire on cylinder 1 through 8, caused by a spark plug below 35 percent. This normally does not activate limp mode. A plug below 10 percent can leave the cylinder dead, produce black smoke, and damage the catalytic converter or DPF. | Replace the indicated spark plug with the toolbox. |
P0201-P0208 | Injector circuit malfunction on cylinder 1 through 8. Expect higher fuel use and rough running. A severely failed injector can make its cylinder dead and turn on CHECK. | Replace the affected injector; injectors cannot be repaired. |
P0169 | Incorrect fuel composition: at least 5 percent of the tank contains the wrong fuel. The lamp is the direct warning, but the mixed fuel causes stuttering, power loss, injector damage, or a no-start condition at higher concentrations. | Use fuel-system additive for up to 5 litres of wrong fuel, or drain the tank on a lift. |
P0380 | Diesel glow-plug circuit malfunction. More than half the glow plugs are below 10 percent, so a cold diesel may crank longer or fail to start. | Replace the glow plugs. |
U0100 | Critical loss of communication with the ECU. The starter cranks, but the engine does not fire. This can follow a failed or interrupted flash, an invalid engine file, or an unlicensed tuned feature. | Write a valid flash matching the fitted engine. This code cannot be disabled. |
Clear codes only after understanding the cause
Clear codes in the OBD reader takes about five seconds and removes both active codes and history. It does not repair anything. If the fault remains, the code returns after the following first-clear distance:
| Code | Returns after clearing |
|---|---|
P0169 | 2 km |
P0201-P0208 or P0301-P0308 | 4 km |
P0380 | 6 km |
P0300 | 8 km |
U0100 | Immediately |
Every additional clear halves the return distance. If a cleared limp-mode fault is still present, the car has full power temporarily but the engine wears three times faster. Treat clearing as an emergency measure for reaching help, not as a repair. For P0169, switch the ignition off after correcting the fuel problem because that code remains latched until ignition is turned off.