What does it mean?
P1726 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: Insufficient Engine Speed Decrease During Self Test .
Symptoms
- High idle that hangs and drops slowly after lifting off the pedal
- Idle speed will not return to specification when hot
- Self test aborts or repeats the same failure
- MIL (check engine lamp) may stay off since this result appears mostly during the test
- Vehicle creeps in gear more than normal and feels slow to slow down
Likely causes
- Vacuum leak in an intake hose, gasket or brake booster line holding idle up
- Carbon deposits in the throttle bore keeping the plate from closing fully
- Sticking or binding throttle plate, cable, or a misadjusted throttle stop
- Idle air control valve stuck open or an electronic throttle body that will not return to base position
- Electrical or air conditioning load applied during the test raising commanded idle
- Test performed at the wrong coolant temperature or with accessories switched on
- Leaking positive crankcase ventilation hose or a stuck idle-up device
How to fix it
- Repeat the self test only with the engine fully warm, accessories off and steering straight ahead
- Smoke test the intake tract, checking hoses, gaskets and the booster line for leaks
- Inspect and clean the throttle bore and plate, then check that it closes freely by hand
- Watch throttle position and commanded idle on live data while blipping and releasing the pedal
- Test idle air control operation, or command the electronic throttle open and closed with a scan tool
- Verify the throttle cable or linkage is not binding and returns to the stop
- Repair the leak or clean the throttle first, then run the self test again to confirm