Code
P0418
GWM
P — Powertrain
- Intake manifold relay A fault
AI status
Completed
Completed
100%
Causes
- Faulty intake manifold relay A (stuck, open, or intermittent)
- Blown fuse or poor fuse connection supplying the relay
- Open, shorted, or corroded wiring/connector in the relay control or supply circuit
- Poor ground at relay or related component
- Faulty intake manifold actuator or downstream load causing overcurrent
- Faulty PCM/ECM driver or internal module fault
Symptoms
- Malfunction Indicator Lamp (MIL) illuminated with P0418 stored
- Reduced engine performance or limp mode (if intake runner system disabled)
- Rough idle or stalling in some vehicles
- Poor acceleration or abnormal throttle response
- Noisy or inoperative intake manifold actuator/IMRC operation (if audible)
What to check
- Read and record freeze-frame and all stored codes; note related stored codes
- Visually inspect relay, relay socket, fuse, and associated connectors for corrosion, damage or loose pins
- Inspect wiring harness for chafing, pinches, repairs, or water intrusion between relay, PCM and intake actuator
- Check for aftermarket devices or recent repairs in the area
- Wiggle test harness and observe live data/MIL for intermittent faults
Signal parameters
- Battery supply voltage at relay fuse (approx. vehicle battery voltage, ~12–14.5 V)
- Control signal from PCM to relay (voltage when commanded; may be switched ground or +12 V)
- Relay coil resistance (manufacturer spec; typically tens to hundreds of ohms)
- Current draw to actuator when relay energized (mA or A)
- Continuity/resistance of supply and ground circuits to relay and actuator
Diagnostic algorithm
- Retrieve trouble codes and live data; note whether code is current or historic and any related codes. Clear codes and perform a re-check to confirm repeatability.
- Visually inspect relay, fuse, socket and wiring for corrosion, melted insulation, or loose connectors. Repair any obvious damage.
- With key OFF, remove the intake manifold relay and inspect socket pins. Check fuse continuity. Replace relay with known-good identical part or swap with an equivalent relay to test.
- Measure battery voltage at the relay supply terminal and confirm good fused power present with key ON.
- Command the relay ON (using scan tool if possible) and verify the PCM control signal and that supply is switched to the load. If PCM uses a ground-side driver, check for switching to ground; if high-side, check for +12 V output.
- Measure relay coil resistance on the removed relay to confirm it is within spec and bench-test the relay operation.
- Measure continuity between relay output and intake manifold actuator and verify ground continuity. Check for shorts to power or ground.
- If the relay and wiring checks good but circuit still fails, bench-test or inspect the intake actuator for abnormal current draw; disconnect actuator and see if the relay fault clears.
- If wiring and load are OK, check PCM driver output with oscilloscope or consult wiring diagram; replace PCM only after confirming driver fault and following manufacturer procedures.
- After repair or replacement, clear codes, perform a drive cycle and verify the issue is resolved.
Likely causes
- Relay contacts failed or coil open/intermittent
- Corroded/loose relay socket or fuse causing intermittent supply
- Damaged control wire between PCM and relay (open/short to power/ground)
- Faulty intake manifold actuator drawing excessive current and tripping the circuit
Fault status
Status
Intake manifold relay A circuit fault detected by PCM; relay control or supply does not meet expected values (open, short, intermittent, or out-of-range current).
Repair difficulty: Medium
Diagnostic time: 0.5-3.0 hours
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