Troubleshooting diagram
The Malfunction Indicator Lamp (MIL) displays Diagnostic Trouble Code (DTC) 21: VTEC Solenoid Circuit Problem.
* Testing on the road:
Accelerate in 1st gear until the engine speed exceeds 6,000 rpm. Hold 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 - MIL is illuminated, and code 21 is detected with the shorted SCS connector connected, then check the VTEC control system:
1. Perform the Engine Control Module (ECM) installation.
2. Start the engine.
3. Warm up the engine to normal operating temperature (the cooling fan turns on).
4. Perform a driving test on the road.
If the MIL does not light and does not detect code 21, then the VTEC valve wiring or the ECU is likely poorly connected.
If the MIL is illuminated and shows code 21, then check the VTEC solenoid.
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 body.
If the resistance is less than 14 ohms or more than 30 ohms, then the VTEC solenoid valve is probably 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 the open in the GRN/- YEL wire between the ECM (AZ) and the VTEC valve connector.
If there is continuity, then check the continuity between the VTEC valve connector contact and the body.
Repair short circuit in wire - GRNWEL between ECM (AB) and VTEC solenoid valve connector.
If there is no continuity, check the VTEC solenoid valve:
To do this:
1. Connect the VTEC solenoid valve connector.
2. Loosen the M10 bolt and install the special tools as shown.
3. Connect the tachometer.
4. Start the engine.
5. Warm up the engine to normal operating temperature (the cooling fan turns on).
6. Check the oil pressure at engine speeds of 1000, 3000 and 5000 rpm.
Note: Please keep the measurement time as short as possible, as the optimum 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 battery terminal to the GRNWEL terminal.
4. Start the engine and check the oil pressure at a crankshaft speed of 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 (ECM) and check again. If the fault disappears, replace the electronic control unit (ECM).
[Based on materials from the website «HONDABOOK»]