Troubleshooting diagram
Malfunction indicator lamp (MIL) issues a diagnostic fault code (DTC) 21: Problem in the VTEC solenoid valve circuit.
*Check while driving on the road:
Accelerate in 1st gear until the engine speed exceeds 6000 rpm. Record this speed for at least two seconds. If the MIL does not illuminate during the first road test, repeat this test two more times.
If the MIL illuminates and a code 21 is detected with the SCS connector connected, check the VTEC control system:
1. Install the engine control unit (ESM).
2. Start the engine.
3. Warm up the engine to normal operating temperature (cooling fan turns on).
4. Perform a road test.
If the MIL is not illuminated and does not detect a code 21, then there may be a poor connection to the VTEC valve or ECU wiring.
If the MIL is illuminated and sets code 21, then check the VTEC solenoid valve.
To do this, turn off the ignition, disconnect the VTEC solenoid valve connector and check the resistance between the VTEC valve connector contact and the housing.
If the resistance is less than 14 ohms or more than 30 ohms, then the VTEC solenoid valve is likely faulty.
If the resistance is 14-30 ohms, then check the wiring between the VTEC solenoid valve and terminal A8 of the electronic control unit.
If there is no continuity, repair open in the GRN/- YEL wire between the ECM (AZ) and VTEC valve connector.
If there is continuity, check continuity between the VTEC valve connector terminal and the body.
Repair short in wire - GRNWEL between ECM (AB) and VTEC solenoid/mag valve connector.
If there is no continuity, check the VTEC solenoid valve:
For this:
1. Connect the VTEC solenoid valve connector.
2. Remove the M10 bolt and install the special tools as shown.
3. Attach the tachometer.
4. Start the engine.
5. Warm up the engine to normal operating temperature (cooling fan turns on).
6. Check oil pressure at engine speeds of 1000, 3000 and 5000 rpm.
Note: Reduce the measurement time as much as possible, since optimal engine operation without load is less than one minute.
If the pressure is above 49 kPa (0.5 kgf/cm2), then replace the VTEC solenoid valve.
If the pressure is below 49 kPa (0.5 kgf/cm2), then check the VTEC solenoid valve.
1. Turn off the ignition.
2. Disconnect the VTEC valve connector.
3. Attach the positive terminal of the battery to the GRNWEL terminal.
4. Start the engine and check the oil pressure at 5000 rpm.
If the pressure is above 390 kPa (4.0 kgf/cm2), then replace the VTEC solenoid valve.
If the pressure is below 390 kPa (4.0 kgf/cm2), then replace with a known-good electronic control unit (ESM) and check again. If the fault disappears, replace the electronic control unit (ESM).