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Home >> Toyota >> 2001 >> Corolla CE, Automatic >> Repair and Diagnosis >> Engine Performance >> System >> Engine Control System Self-Diagnostics >> Diagnostic Tests >> DTC P1656: Oil Control 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 Oil Control Valve (OCV) harness connector and note idle speed. OCV is located in each cylinder head, underneath lower intake manifold. Engine idle speed should not change. Using jumper wires, apply battery voltage and ground to OCV. Engine should idle rough or stall. If OCV operates as specified, go to next step. If OCV does not operate as specified, replace OCV.
  2. Access ECM below stereo, behind instrument panel, just in front of center console. See Figure. Using oscilloscope, backprobe ECM harness connector. On models with 4A/T transmission, connect oscilloscope between terminals No. 23 (Red wire) and No. 24 (Black wire) at ECM harness connector E7. See Figure. On models without 4A/T transmission, connect oscilloscope between terminals No. 1 (Red wire) and No. 2 (Black wire) at ECM harness connector E4. See Figure. On all applications, 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 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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