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Home >> Toyota >> 2001 >> Celica GT-S, Standard >> Repair and Diagnosis >> Engine Performance >> System >> Engine Control System Self-Diagnostics >> Diagnostic Tests >> DTC P1656: Oil Control For VVT Valve Malfunction >> Diagnosis & Repair (Using OBD-II Scan Tool)

Diagnosis & Repair (Using OBD-II Scan Tool)

  1. Start engine and allow it to idle. Disconnect Variable Valve Timing (VVT) Oil Control Valve (OCV) harness connector and note idle speed. VVT OCV is located on timing chain side of cylinder head. Engine idle speed should not change. Using jumper wires, apply battery voltage and ground to VVT OCV. Engine should idle rough or stall. If VVT OCV operates as specified, go to next step. If VVT OCV does not operate as specified, replace VVT OCV.
  2. Turn ignition off. Connect VVT OCV harness connector. Access ECM in driver's side of engine compartment, next to battery. See Figure. Using oscilloscope, backprobe ECM harness connector. Connect oscilloscope between terminals No. 23 (White wire) and No. 24 (Green/Orange wire) at ECM harness connector E4. See Figure. Start engine and let idle. Ensure oscilloscope pattern is as shown in illustration. See Figure. As engine speed is increased, waveform frequency ("A") should lengthen. If waveform pattern is as shown, go to next step. If waveform pattern is not as shown, replace ECM.
  3. Check for an open or short in wiring between VVT OCV and ECM. If problem exists, repair wiring as necessary. If problem does not exist, problem is intermittent. Check component and ECM connections.
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