Stored codes are displayed by the flashing ECU LED. If the warning lamp "CHECK ENGINE" was lit or remains lit, remove the floor mat from the front right passenger side. The ECU is under a protective cover; the LED can be seen through a small window without removing the ECU cover. Set the ignition key to position "ON"; the LED will blink to display all stored codes. Additionally, if the service connector is shorted to Accord or 2.1L. Prelude, lamp "CHECK ENGINE" will display the saved codes in the same way. The 2-pin service connector is located on the right under the dash on the Accord or on the Prelude's thermal baffle, next to the control box.
Codes 1 to 9 are indicated by short flashes; in two-digit codes, the first significant digit is displayed with a series of longer flashes and then with shorter flashes, the least significant digit. For example, code 43 would be designated for "A" - long flashes, and "3" - short. Codes are separated by pauses between transmissions. The position of the codes during the output can be useful for diagnostic work. Multi-valued codes appearing in isolated order indicate unique cases; if the code 1-1-1-pause-9-9-9 was displayed on the set-diode, this indicates two problems or problems observed at different times. An alternating display, such as 1-9-1-9-1, indicates problems occurring at the same time.
When counting flashes to determine codes, a code that is not valid for the vehicle may be encountered. In this case, a recount is performed to confirm the correct count. If necessary, turn the ignition key to position "OFF", return to the original state and start counting again. If the code is again not standard for the vehicle, the ECU must be replaced.
Lamp S or S4 can be lit together with the lamp "CHECK ENGINE" on Accorde and Prelude with automatic transmission if codes 6, 7 or 17 are stored in memory. In this case, follow the troubleshooting procedures for the fuel injection system first. Clear the memory after the repair, then check the lamp S or S4 again.
Clearing codes in memory
Stored codes are cleared from memory when power is removed from the ECU. De-energizing also resets (or resets) memory used for other electronic devices such as watches and radios. For this reason, always make a note of the radio settings before clearing the system.
Since disconnecting the battery will also clear the memory, this is not a recommended procedure.
The memory can be cleared by removing the corresponding fuse for at least 10 seconds. In all cases, the memory clearing fuse is located under the hood in the fuse and relay box. On the Accord, this is the BACK-UP fuse; on the Prelude it is the CLOCK fuse (CLOCK).
Flashing self-diagnosis indicator
Fault codes - 1990-91 Accord
0 | ECU |
1 | Oxygen content |
3 | Manifold absolute pressure |
4 | Angle of rotation of the crankshaft |
6 | cooler temperature |
7 | Throttle angle |
8 | TDC position |
9 | Cylinder Position Number 1 |
10 | Intake air temperature |
12 | Exhaust gas recirculation system |
13 | Atmosphere pressure |
14 | Electronic air control |
15 | Ignition output |
14 | Fuel burner |
17 | Vehicle speed sensor |
20 | Electrical load detector |
30 | A/T FI signal A |
31 | A/T FI signal B |
41 | Oxygen heater sensor |
43 | Fuel supply system |
Fault codes - 1990-91 Prelude
0 | ECU |
1 | Oxygen content A*, Oxygen content** |
2* | Oxygen content B |
3 | Manifold absolute pressure |
5 | |
4 | Angle of rotation of the crankshaft |
6 | cooler temperature |
7 | Throttle angle |
8 | TDC position |
9 | Cylinder Position No.1 |
10 | Intake air temperature |
12 | Exhaust gas recirculation system |
13 | A1atmospheric pressure |
14 | Electronic air control |
15 | Ignition output |
16 | Fuel burner |
17 | Vehicle speed sensor |
41** | Oxygen heater sensor |
43** | Fuel supply system |
One asterisk denotes a 2.0L engine; a double asterisk indicates a 2.1L engine.