Comprehensive diagnostic guide for OBD-II code P0661

What This Code Means

• P0661: Intake Manifold Tuning (IMT) Solenoid Circuit Low Bank 1

  • In plain terms: the PCM/ECU sees the intake manifold tuning solenoid (bank 1) returning a signal that is lower than expected, i.e., a "low signal" fault on the control circuit.
  • This is commonly associated with the intake manifold tuning valve (IMV/IMRC) solenoid circuits in engines that use variable intake runner technology. Bank 1 indicates the primary bank of cylinders for V-configurations or the engine side designated as bank 1. Note: manufacturers may use different terminology (IMRC, IMT, IMV) but the underlying fault is the same: an input/output control circuit reading too low or not switching as commanded.

• How this fits with OBD-II basics

  • OBD-II DTCs (including powertrain codes) are produced when the PCM detects parameters out of expected ranges. The general mechanism, as described in the Diagnostic Trouble Codes and Powertrain Codes sections, is that the vehicle's control modules monitor sensor and actuator circuits and set codes when readings are out of spec (MIL illumination typically follows). The general approach to diagnosing such codes involves wiring checks, actuator/solenoid tests, and PCM/SCU health assessment, then rechecking after repairs.

What symptoms might a real user report?

• MIL (Check Engine Light) illuminated with P0661 stored.
• Noticeable or intermittent hesitation or rough running when the IMT system is commanded or during transitions between long/short runner modes (on some engines, IMT operation changes air flow characteristics, which can feel like a stumble or surge).
• Potentially reduced or inconsistent engine performance, especially under load or during rapid throttle changes.
• In some cases, no obvious drivability issue beyond the MIL, depending on how the vehicle's engine management copes with the fault.

Important Notes

• The IMT/IMRC solenoid circuit is part of the intake manifold tuning system. A "low signal" reading means the PCM isn't seeing the expected control input (or the input is stuck low), which could be due to wiring, solenoid hardware, or PCM issues. The specific bank designation (Bank 1) depends on the engine configuration.
• Because this is a circuit-level fault, P0661 often appears alongside other related codes if the manifold/tuning system or related circuits are physically compromised.

Probable Causes

• Wiring, connectors, and harness issues in the IMT control circuit (most common): damaged wire, loose connector, corrosion, insulation wear, harness chafing. Likelihood: 35-50%
• Faulty IMT/IMRC solenoid (or its internal coil): coil open/short, stuck solenoid, degraded operation. Likelihood: 25-35%
• PCM/ECU fault or flaky ground/reference within the PCM: signal not being produced or interpreted correctly. Likelihood: 5-15%
• Battery/charging or power supply issues causing insufficient voltage to the solenoid circuit: marginal but possible. Likelihood: 5-10%
• Related vacuum/hoses or auxiliary IMRC subsystem issues (less common, but possible if the system is vacuum-actuated or uses vacuum lines): Likelihood: 5-10%
  Note: These are educated estimates in absence of direct NHTSA complaint data . They reflect common IMRC-related failures observed in practice.

Diagnostic Approach

1) Confirm the fault

• Retrieve the DTC(s) with a scan tool and review freeze-frame data (engine RPM, load, coolant temperature, fuel trims, etc.).
• Note any related codes (other IMRC-related codes, misfire codes, or sensor faults). This helps prioritize tests.

2) Visual and mechanical inspection

• Inspect the harness(es) and connectors to the IMT/IMRC solenoids on bank 1. Look for:
  • Damaged insulation, chafed wires, bent pins, corrosion, or loose connections.
  • Any signs of heat damage or oil/water intrusion.
• If the vehicle has a known bank 1 and bank 2 solenoid arrangement, inspect for corrosion or damage on both sides to help determine if it's a bank-specific issue or a common circuit problem.

3) Electrical circuit checks (wiring and solenoid)

• With ignition ON (engine OFF), check for:
  • The presence of a stable reference/ground and a supply to the IMT solenoid circuit at the PCM and/or at the solenoid connector, as appropriate for the vehicle.
  • Continuity of the control circuit wire from the PCM to the solenoid input (no opens). Also check for shorts to ground or to battery voltage.
• Check the solenoid coil resistance (if accessible and specified by the factory service information). Compare to the manufacturer's specification. An out-of-spec resistance (significantly high or low) typically indicates a failed solenoid coil.
• If a scanner supports circuit current and voltage monitoring, observe the IMT solenoid input signal while the engine is running and the PCM is commanded to actuate the solenoid. A low signal when commanded or no change in signal indicates an electrical/control issue or PCM fault.

4) Confirm PCM control behavior

• Use the scan tool to command the IMT solenoid (if supported) and observe whether the PCM responds (signal change, duty cycle, or on/off state). Lack of commanded activity or abnormal responses points toward PCM or wiring issues.
• If possible, compare to the non-bank-1 channel (bank 2) operation to help isolate whether the issue is bank-specific or a common circuit problem.

5) Solenoid functional test (bench or component swap)

• Bench-test the solenoid coil by applying the rated voltage in a controlled manner and observe for proper operation (mechanical response) and current draw. A non-responsive coil or abnormal current draw indicates a failed solenoid.
• If there are two IMT solenoids (one per bank, or bank 1 vs bank 2), and you can do a controlled swap between banks, observe whether the DTC follows the solenoid (suggesting a solenoid fault) or remains tied to Bank 1 (suggesting wiring/PCM fault). Only perform bank-to-bank swaps if the vehicle's service procedure allows this safely.

6) Mechanical/related subsystem checks

• Inspect any vacuum lines or hoses connected to the IMRC solenoids (if the system is vacuum-actuated). A vacuum leak or disconnected line can affect solenoid performance and manifest as control faults.
• Check for vacuum source integrity and any intake manifold issues that could affect tuning operation.

7) Review software/updates

• Some IMRC issues can be addressed by software/ECU calibrations, or there may be service bulletins for specific vehicle models. If the mechanical and electrical checks are inconclusive, consider a software update or ECU calibration per the vehicle manufacturer's guidelines.

8) Decision points and outcomes

• If wiring/solder joints/connectors are damaged: repair/replace wiring harness and connectors, reseal as needed, then re-test.
• If the IMT solenoid is faulty: replace the solenoid(s). Re-test using the same electrical and PCM command checks.
• If the PCM is suspected: verify power and grounds, check for PCM fault codes, perform a PCM swap or reflash only per manufacturer guidelines.
• If a power supply issue is found (low battery/charging): address charging system (test alternator, battery health, starting/charging circuit), then re-test to see if the code clears after a proper voltage environment is restored.
• If all diagnostics point to a non-repairable fault in the IMT system and no wiring/solenoid faults are detected: consider manifold replacement or actuation system replacement per OEM guidance, and re-check codes after repair.

Post-Repair Verification

• Clear the DTCs and perform a road test or drive cycle to verify the IMT system operates properly and that P0661 does not return.
• Monitor live data to ensure the IMT solenoid responds to commanded changes, particularly during transitions between engine load conditions that typically invoke IMT (e.g., throttle transitions, certain RPM ranges).
• If the code reappears, revisit steps to identify any overlooked wiring issues, or consider PCM fault with professional reprogramming or replacement as per OEM guidance.

Safety Considerations

• Work with the ignition OFF and battery disconnected when inspecting or unplugging electrical connectors in the IMT circuit to avoid shorting or shock.
• Be cautious around hot engine components and moving/moving parts (especially if you need to perform bench tests on actuators).
• Follow all vehicle-specific service procedures and torque specs for any component replacement or connector reseating.
• When performing any wiring repairs, use proper automotive-grade wiring harness tools and ensure all repairs are insulated and protected from heat, oil, and moisture.

Documentation

• Vehicle year/make/model, engine family, IMT/IMRC solenoid locations (bank 1), and whether you observed bank 1 vs bank 2 differences.

• DTC details, freeze-frame data, and any related codes.

• All test results (voltage readings, coil resistance, continuity checks, actuator responses, and scanner data) with dates and operator notes.

• Troubleshooting steps taken and outcomes, including any parts replaced and software updates applied.

• Final drive test results and whether the code cleared.

• General OBD-II and diagnostic code framework: Wikipedia - OBD-II, Diagnostic Trouble Codes, and Powertrain Codes sections. These ensure an accurate description of how DTCs are produced and how powertrain codes relate to emissions and driveability concerns.

  • OBD-II - Diagnostic Trouble Codes:
  • OBD-II - Powertrain Codes:
  • OBD-II - Emissions Testing (context on how codes relate to emissions):

• Specific code description used for P0661 (transfer from the provided Open Source MIT repository):

  • This provides the direct interpretation of P0661 as an intake manifold/tuning solenoid circuit fault on bank 1. Note: Some variations exist by manufacturer, but the underlying fault class remains the same (IMT/IMRC solenoid circuit low).
  • Source: Open Source (MIT) repository entry included .

Notes

• If you need engine-specific values (pin numbers, exact resistance ranges, and exact commanded voltage behavior), consult the vehicle's factory service data for P0661. The exact wiring diagram and component specifications vary by make/model and engine family.
• Because do not contain vehicle-specific P0661 test values, the diagnostic steps above emphasize a systematic electrical, mechanical, and control-system approach that applies across many engines using IMT/IMRC technology.
• If you have access to vehicle-specific NHTSA complaint trends for P0661, you can refine the probability estimates for each cause. In the absence of that data in , the probabilities above rely on general field experience with intake manifold tuning solenoids and their common failure modes.

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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