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P1521

Variable Intake Solenoid #1 Circuit Malfunction.

  • Other
  • Powertrain
  • Manufacturer code
  • Low severity

How this code is built

P
SystemPowertrain
1
Defined byThe manufacturer
5
AreaVehicle speed, idle control and auxiliary inputs
21
FaultThe specific fault in that area

What it means

P1521 on this vehicle means the control unit has found a fault in the electrical circuit of variable intake solenoid number 1. This solenoid switches the variable intake manifold (runner length or flap) between its low-rpm and high-rpm settings. The code sets when the commanded state and the circuit's electrical feedback disagree, typically through an open circuit, a short to ground or a short to supply. The exact layout and the location of solenoid 1 depend on the make and engine, so check the manufacturer's data.

Symptoms

  • Engine warning light on
  • Weaker mid-range or top-end power
  • Poor low-speed pulling power
  • Rough or unstable idle
  • Worse fuel economy
  • Change in intake noise at certain revs

Possible causes

  • Faulty solenoid with an open or shorted coillikely
  • Damaged, chafed or corroded wiring between the solenoid and the control unitlikely
  • Poor connection at the solenoid plug or control unit connector, such as corrosion, bent or loose pinslikely
  • Missing power supply or ground to the solenoid, such as a blown fuse or relay faultpossible
  • Cracked or disconnected vacuum line or a leaking reservoir, where the system is vacuum operated, which can show alongside the circuit faultpossible
  • Internal driver fault in the engine control unitrare

How to diagnose

  1. Read all stored and pending codes and the freeze frame data, and note whether the fault is constant or intermittent
  2. Check the manufacturer's data for where solenoid 1 sits on this engine and how it is wired
  3. Visually inspect the solenoid, its plug, the wiring loom and the vacuum lines for damage, heat, chafing, oil contamination or corrosion
  4. Check the relevant fuse and relay, and confirm there is a supply voltage at the solenoid plug with the ignition on
  5. Measure the solenoid coil resistance and compare it with the specification for the engine
  6. Test the wiring between the solenoid and the control unit for continuity and for shorts to ground or supply
  7. Operate the solenoid using a bidirectional test if available and check that it clicks and that the manifold actuator responds
  8. Clear the code and road test to see if it returns, then recheck the connectors by wiggling the loom while monitoring

How to fix

  • Replace the solenoid if its resistance is out of specification or it fails the operation test
  • Repair or replace damaged wiring and fit new terminals where the pins are corroded or burnt
  • Clean, re-seat or repair the connectors at the solenoid and the control unit
  • Replace the blown fuse or faulty relay after finding out why it failed
  • Renew split or loose vacuum hoses and any leaking reservoir or actuator diaphragm
  • Diagnose and replace or repair the control unit only after the wiring and solenoid have been proven good

Can I keep driving?

Low severity

The car can normally be driven as the fault mainly reduces performance and economy, but have it checked soon. If the car goes into limp mode or runs very roughly, limit your driving until it is repaired.

Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.

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