The ECU constantly performs self-diagnostics for some control functions. The language used by the ECU to indicate the source of the problem is diagnostic codes. Codes are two-digit numbers in the range from 12 to 61. For different control units, fault codes may differ slightly from each other. The table shows the decoding of fault codes for the electronic control unit for a central fuel injection system with imported components.
When a malfunction is detected by the ECU, the code is stored in memory and the control lamp turns on "CHECK ENGINE". This does not mean that the engine should be stopped immediately, but the cause of the warning light should be found as soon as possible.
Codes of malfunctions of the electronic control unit
12 | Serviceability of a diagnostic circuit of a control lamp |
13 | There is no signal from the oxygen concentration sensor |
14 | Low coolant temperature sensor signal |
15 | High coolant temperature sensor signal |
21 | Throttle position sensor signal voltage too high |
22 | Insufficient Throttle Position Sensor Signal Voltage |
23 | Overestimated signal voltage from the air temperature sensor |
24 | No signal from vehicle speed sensor |
25 | Insufficient signal voltage from the air temperature sensor |
33 | Overestimated signal voltage from the absolute air pressure sensor |
34 | Insufficient signal voltage from the absolute air pressure sensor |
35 | Idle speed deviation |
42 | Ignition control circuit malfunction |
44 | lean mixture |
45 | Enriched composition of the mixture |
51 | Programmable read-only memory error (PROM) |
53 | System supply voltage too high |
54 | Overestimated or insufficient voltage signal octane correction |
55 | Electronic control unit error |
Lamp "CHECK ENGINE"
The lamp is located on the instrument panel and performs the following functions:
- informs the driver that there is a malfunction in the engine management system and the vehicle needs to be checked as soon as possible.
- issues diagnostic codes stored in the computer's memory to help the technician find the problem.
When the ignition is turned on, the lamp lights up and, while the engine is not running, the lamp and systems are checked for serviceability. After starting the engine, the lamp should go out. If the lamp continues to burn, then the self-diagnosis system has detected a malfunction. If the fault disappears, then the lamp goes out usually after 10 seconds, but the fault code will be stored in the computer's memory.
When "fickle" lamp failure nature "CHECK ENGINE" will stay on for about 10 seconds and then turn off. However, the corresponding fault code will be stored in the memory of the computer until its power is turned off. When unexpected codes are found during the reading of codes, it can be assumed that these codes are created by an intermittent malfunction and can help in diagnosing the system.