Skip to content
GTECH Calibration
Portal

P1491

EGR Valve Lift Insufficient Detected.

  • Acura
  • Powertrain
  • Manufacturer code
  • Medium severity

How this code is built

P
SystemPowertrain
1
Defined byThe manufacturer
4
AreaAuxiliary emission controls
91
FaultThe specific fault in that area

What it means

On Acura models P1491 means the engine control unit has detected insufficient EGR valve lift. When the EGR valve is commanded open, the lift sensor or the engine's reaction (depending on model) does not show the expected flow or valve movement. The code is stored when the EGR system fails its check, so exhaust gas is not being recirculated properly.

Symptoms

  • Malfunction indicator lamp on
  • Rough idle or occasional stalling when the EGR opens
  • Pinking or knocking under light load
  • Hesitation or poor drivability at cruising speeds
  • Failed emissions test with raised NOx

Possible causes

  • Blocked EGR passages or carbon-clogged EGR valvelikely
  • Sticking or faulty EGR valve or lift sensorlikely
  • Faulty EGR control solenoid or vacuum supply (where fitted by model)possible
  • Split, disconnected or blocked vacuum hoses to the EGR valvepossible
  • Damaged wiring, poor connector contact or corroded terminals at the valve or sensorpossible
  • Faulty engine control unitrare

How to diagnose

  1. Read the stored codes and freeze frame data to see engine speed, load and temperature when the code set, and check for other codes
  2. Visually inspect the EGR valve wiring, connector and vacuum hoses for damage, splits, kinks or loose fittings
  3. Check the vacuum supply to the EGR valve and control solenoid where fitted, as the layout depends on model and engine
  4. Using a scan tool, command the EGR valve and watch the lift sensor reading and the change in engine idle or manifold pressure
  5. Check the lift sensor supply, reference and signal circuits for correct voltage and continuity against the wiring diagram for that model
  6. Remove the EGR valve and inspect it and the passages for carbon build-up and a valve that sticks or fails to seat
  7. Check the valve's resistance or operation against the manufacturer's specification for that engine

How to fix

  • Clean carbon from the EGR valve and passages, or replace the valve if it sticks or leaks
  • Replace the EGR valve or lift sensor if it fails electrical or operation checks
  • Replace the EGR control solenoid or repair the vacuum supply where fitted
  • Replace perished or blocked vacuum hoses
  • Repair damaged wiring or connectors, then clear the code and confirm it does not return on a test drive

Can I keep driving?

Medium severity

The car can usually be driven for a short time, but book it in soon as poor drivability, pinking and higher emissions can continue and the fault may worsen. Avoid heavy loads if it is knocking or running badly.

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

This code for other makes

Nearby codes