The ECU constantly performs self-diagnosis for some control functions. The ECU language for indicating the source of the malfunction is diagnostic codes. Codes are two-digit numbers in the range from 12 to 61. The fault codes of different control units may differ slightly from each other. The table shows the decoding of the fault codes of the electronic control unit for the central fuel injection system with imported components.
When a fault is detected by the ECU, the code is stored in memory and the indicator lamp comes on "CHECK ENGINE". This does not mean that the engine should be stopped immediately, but the reason for the warning light coming on should be found at the earliest opportunity.
Electronic Control Unit Error Codes
12 | Diagnostic circuit of the control lamp is working properly |
13 | No signal from oxygen concentration transmitter |
14 | Low signal level of the coolant temperature sensor |
15 | Coolant Temperature Sensor High Signal |
21 | Throttle Position Sensor Signal Voltage Too High |
22 | Throttle Position Sensor Signal Voltage Low |
23 | High signal voltage from air temperature sensor |
24 | No signal from vehicle speed sensor |
25 | Insufficient signal voltage from the air temperature sensor |
33 | Absolute air pressure sensor signal voltage too high |
34 | Insufficient signal voltage from the absolute air pressure sensor |
35 | Idle speed deviation |
42 | Ignition control circuit malfunction |
44 | Lean mixture composition |
45 | Enriched composition of the mixture |
51 | Programmable Read Only Memory (PROM) Error |
53 | System supply voltage too high |
54 | Octane correction signal voltage too high or too low |
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 fault in the engine management system and the vehicle needs to be checked as soon as possible.
- issues diagnostic codes stored in the ECU memory to help the technician locate the fault.
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 the engine starts, the lamp should go out. If the lamp continues to light, then the self-diagnostic system has detected a malfunction. If the malfunction disappears, then the lamp usually goes out after 10 seconds, but the malfunction code will be stored in the ECU memory.
In case of "intermittent" nature of the fault, the lamp "CHECK ENGINE" will remain lit for about 10 seconds and then go out. However, the corresponding fault code will be stored in the ECU memory until its power supply is disconnected. When unexpected codes are detected during the code reading process, it can be assumed that these codes are generated by an intermittent fault and can help in diagnosing the system.