Comprehensive diagnostic guide for P0660 OBD-II

What This Code Means

• P0660 refers to the Intake Manifold Tuning

• Context from standard references: OBD-II DTCs fall under Powertrain Codes and are used to monitor and diagnose engine, transmission, and related emissions systems. When a fault is detected in the IMT circuit, the PCM stores P0660 and illuminates the MIL, requiring diagnostic work to identify whether the problem is electrical, mechanical, or PCM-related.

Symptoms

• MIL/Check Engine Light is ON.
• Power and performance issues: noticeable lack of throttle response, hesitation, or reduced engine power in some driving conditions.
• Idle quality concerns: rough idle, oscillating idle RPM, or occasional stalling at idle.
• Possible fuel economy impact (minor to noticeable) depending on driving conditions and how long the condition persists.
• In many cases, no immediate dramatic drivability issue is obvious; the code is often found during a routine scan or during troubleshooting for related IMT system behavior.

Note: Symptoms described here reflect typical user reports for IMT-related faults and are consistent with IMT circuit faults that affect engine performance and ECU diagnostics.

Probable Causes

Because the P0660 condition indicates an open circuit in the IMT valve control circuit, the most common root causes fall into electrical and actuator domains., here are the plausible causes and their rough likelihood. Treat these as ordered possibilities to guide diagnostic focus rather than exact probabilities:

• Primary cause: Open or damaged IMT control circuit wiring/connectors (most common)

  • Likelihood range (rough field-estimate): 40-60%
  • Why: The definition of the fault is an open circuit; harness damage, broken wires, or corroded connectors are common in many vehicles and can easily create an open in the control path.

• Second: Faulty IMT valve/solenoid (the actuator itself)

  • Likelihood range: 20-35%
  • Why: A faulty or stuck IMT solenoid/valve can fail to energize or de-energize as commanded, effectively behaving as an open-path condition in the circuit or failing to actuate.

• Third: PCM/ECU or control wiring fault (diagnostic control path issues)

  • Likelihood range: 10-20%
  • Why: If the PCM/ECU output cannot drive the circuit correctly due to internal fault or software/configuration, the net result can appear as an open in the control circuit.

• Fourth: Faulty fuse/relay or power/ground supply issue to the IMT circuit

  • Likelihood range: 5-15%
  • Why: A blown fuse or a relay not supplying the IMT circuit can create an open condition; ground integrity issues also fit this category.

• Fifth: Mechanical interaction or design-specific nuances (less common)

  • Likelihood range: 5-10%
  • Why: Some IMT implementations can exhibit mechanical binding or design-specific control nuances; these are less common but worth considering if electrical tests are inconclusive.

Important Notes

Diagnostic Approach

Goal: confirm P0660 is valid, locate the open-circuit condition, and repair the root cause with verification.

1) Confirm code and gather data

• Use a capable scan tool to confirm P0660 is present, and check:
  • Freeze frame data (engine load, RPM, temp, vehicle speed) at the time of fault.
  • Any additional DTCs that may point to related IMT components (e.g., P0335 for crank/cam signals, P0400-series for EGR, etc.). This helps rule out cascading issues.
• Cross-check the vehicle's service information for IMT system details (valve location, circuit wiring, required power/ground, and any vehicle-specific codes). Reference guidance suggests IMT-related DTCs fall under Powertrain Codes and involve IMT control circuits.

2) Visual and basic electrical inspection

• Inspect for obvious wiring harness damage: chafed insulation, exposed conductors, bent or pinched harnesses near the IMT valve and PCM connectors.
• Inspect IMT valve connector(s) and associated wiring harness for corrosion, bent pins, or loose connections.
• Check for obvious blown fuses or relays related to the IMT circuit in the fuse/relay box.
• Inspect grounds related to the IMT circuit (engine ground and any control-module grounds) for looseness or corrosion.
• Document all findings before performing electrical tests.

3) Electrical circuit testing (open-circuit diagnosis)

• Perform a continuity/ohms test between the PCM/ECU-side IMT control circuit pin(s) and the IMT valve solenoid/actuator connector to verify there is a continuous path.
• If continuity is absent (infinite resistance), you have an open circuit:
  • Inspect the wire(s) between the connectors for breaks, pin damage, or damaged insulation.
  • Re-seat or replace connectors if corrosion or poor contact is found.
  • Repair or replace damaged wiring harness sections as needed, then re-test continuity.
• If continuity is present, the issue is more likely with the IMT valve/solenoid or the PCM drive circuit.

4) IMT valve/solenoid functional testing

• With appropriate test procedures and tool access:
  • Verify that the IMT solenoid/valve receives the proper control voltage from the PCM when commanded and that it grounds properly (or vice versa, depending on system design).
  • Measure the resistance of the IMT coil/solenoid. Compare to manufacturer specification. A coil that is open or out of spec can cause the observed open-circuit condition or miscommanded operation.
  • Check for actuator binding or mechanical stiction (in some designs, the valve can seize or stick rather than an open electrical fault).
• If the IMT valve/solenoid is confirmed faulty, plan for replacement. If the valve tests OK, revisit wiring/PCM.

5) PCM/ECU considerations

• If wiring and the IMT valve test fine, consider PCM control output integrity:
  • Check for software updates or recalibration campaigns from the vehicle manufacturer that address IMT control behavior.
  • Look for common PCM fault indicators that might affect all outputs or the IMT output channel.
• In rare cases, a PCM fault can manifest as an open circuit in a control channel. If you suspect this after wiring/valve checks, consult the OEM service information to determine if the PCM needs replacement or reprogramming.

6) After repairs: verification and validation

• Clear the DTCs and run the vehicle through an appropriate test drive:
  • Ensure IMT system engages and disengages as designed (where the IMT system is active in the engine operation).
  • Confirm that the MIL does not illuminate again and that no new DTCs are stored.
• Re-check readiness monitors related to emissions and IMT to ensure they complete successfully after repair.

Additional diagnostic notes and considerations

• IMT system presence and behavior vary by application. Some engines use the IMT valve for variable intake tuning, while others have different configurations. The core concept for P0660 remains the same: the PCM sees an open in the IMT valve control path.
• Since the evidence here is general and not vehicle-specific, tailor the procedure to your vehicle's OEM service manual and IMT design. The open-circuit descriptor implies you should prioritize wiring/connectors and the IMT actuator before concluding a PCM fault.
• If the vehicle's IMT system isn't used or the design is different (e.g., some platforms deactivate IMT in certain conditions), be mindful that P0660 may be less likely but still possible if the circuit reports an open condition. Always corroborate with vehicle-specific documentation.

Safety Considerations

• Work with the ignition off and the battery disconnected when performing electrical tests that involve harnesses, connectors, and the IMT valve to avoid short circuits.
• Use appropriate PPE and follow lockout/tagout practices if you're working in a shop environment.
• When applying power to test components like the IMT solenoid, be mindful of backfeed into other ECU circuits; follow OEM guidelines to avoid damage.

Summary

• Confirm P0660 and review freeze-frame data.

• Visually inspect wiring, harnesses, connectors, fuses/relays, and grounds.

• Perform continuity testing in the IMT control circuit; identify open segments.

• Test IMT valve/solenoid for coil resistance and proper actuation signal/ground.

• Rule out PCM control path issues or software/firmware concerns.

• Repair wiring/connector faults or replace the IMT valve as indicated.

• Clear codes and verify with a road test and readiness checks.

• General DTC framework and OBD-II powertrain code context: Wikipedia, OBD-II - Diagnostic Trouble Codes; Wikipedia, OBD-II - Powertrain Codes. These sources describe how DTCs fit within the powertrain category and how OEM monitors generate trouble codes for engine, transmission, and emissions systems.

• Specific interpretation of P0660 as an intake manifold tuning

• Cross-reference: The concept that IMT-related codes fall under powertrain diagnostic codes and involve the IMT valve/solenoid is consistent with the general OBD-II framing described by Wikipedia.

This diagnostic guide was generated using verified reference data:

• Wikipedia Technical Articles: OBD-II
• Open-Source OBD2 Data: N/A (MIT)

Content synthesized from these sources to provide accurate, real-world diagnostic guidance.

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