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P1491 — Secondary Switch Solenoid Circuit Malfunction

Manufacturer-specificPowertrain (engine & transmission)

OBD-II code P1491 indicates a malfunction in the secondary switch solenoid circuit, which is typically part of the exhaust gas recirculation (EGR) or evaporative emissions (EVAP) system in some vehicles. This code suggests the engine control module (PCM) has detected an electrical issue, such as an open or short, in the solenoid's wiring or the solenoid itself.

Symptoms

What causes it — most likely first

1. Faulty secondary switch solenoid

The solenoid itself may have failed due to internal electrical issues, corrosion, or wear. This is the most common cause of P1491.

2. Damaged or corroded wiring or connectors

Wiring harnesses leading to the solenoid can become frayed, broken, or corroded, causing an open or short circuit. Connectors may also become loose or contaminated.

3. Poor electrical connection at the solenoid or PCM

A bad ground or intermittent connection at the solenoid or PCM can trigger this code. This may be due to corrosion, loose terminals, or damaged pins.

4. Blown fuse or faulty relay

If the solenoid circuit is protected by a fuse or relay, a blown fuse or failed relay can cause the circuit to malfunction.

5. PCM software or internal fault (rare)

While uncommon, a software glitch or internal fault in the PCM could incorrectly flag the solenoid circuit. This should only be considered after all other causes are ruled out.

How it's diagnosed

  1. Retrieve and confirm the P1491 code using an OBD-II scanner, and check for any additional codes that may provide further context.
  2. Visually inspect the secondary switch solenoid, wiring, and connectors for signs of damage, corrosion, or loose connections. Repair or replace as needed.
  3. Test the solenoid for proper resistance and operation using a multimeter. Compare readings to manufacturer specifications to determine if the solenoid is faulty.
  4. Check the wiring harness for continuity and proper voltage supply to the solenoid. Repair any open or short circuits in the wiring or connectors.
  5. Inspect the fuse and relay associated with the solenoid circuit. Replace if blown or faulty.
  6. If all other components test normal, consider testing the PCM for proper operation, though this is rarely the root cause of P1491.

Code facts & related codes

SystemPowertrain (engine & transmission)
StandardizationManufacturer-specific (P1/B1/C1/U1)
Related codesP1494 — Spcut Solenoid Circuit Malfunction

Vehicles this code applies to

The definition is universal; the diagnostics are engine-specific. Open your vehicle for the codes documented for it:

2011 Chrysler 200 — 3.6L V62011 Chrysler 300 — 3.6L2011 Dodge Journey — 2.0L2011 Dodge Journey — 2.4L2011 Jeep Grand Cherokee — 3.0L2011 Jeep Grand Cherokee — 3.6L2013 Ram C/V2014 Ram 1500 — 3.0L Diesel

Frequently asked

Is the PCM usually the cause of P1491?

No, the PCM is rarely the cause of P1491. This code is almost always triggered by a faulty solenoid, wiring issue, or poor electrical connection. Replacing the PCM should only be considered after all other potential causes have been thoroughly ruled out.

Can I drive with a P1491 code?

While the vehicle may still be drivable, driving with a P1491 code can lead to reduced engine performance, increased emissions, and potential long-term damage to other components. It is best to diagnose and repair the issue as soon as possible.

How do I test the secondary switch solenoid?

To test the solenoid, disconnect it from the wiring harness and use a multimeter to measure its resistance. Compare the reading to the manufacturer's specifications. You can also apply power and ground to the solenoid (if safe to do so) to verify it operates correctly.

Will clearing the code fix the issue?

Clearing the code without addressing the underlying issue will only provide a temporary fix. The code will likely return if the root cause (e.g., faulty solenoid, wiring, or connection) is not repaired.