2001 Volkswagen Golf fuel trim and catalyst problems

A.SKYWALKER

MEMBER
2001 VOLKSWAGEN GOLF

Engine Mechanical problem
2001 Volkswagen Golf 4 cyl Two Wheel Drive Manual 140k miles

naturally aspirated 2.0 runs rather smoothly and gets fuel mileage within range. Occasionally wont start just turns and turns. It has been scanned several times lately and consistently gives these codes:

16804/P0420/001056 - Catalyst System; Bank 1: Efficiency Below Threshold

17560/P1152/004434 - Long Term Fuel Trim Additive Air; Bank 1; Range 2: System too Lean

to fix these issues ive replaced the wires/plugs, both o2 sensors, fuel filter and now the mass airflow sensor. After replacing the MAF the engine flutters slightly after start up but returns to normal idle within a second. Im running out ideas I cant locate a vac leak and there shouldnt be any spark issues

1 Reply

DUBTECH

MECHANIC
159 POSTS

I would look very closely for any type of intake leak. The PCV systems tend to deteriorate over time and fall apart. If you don't have a smoke machine or other type of leak detection system, you'll just have to trace every hose or boot for cracks. Even something as small as the dipstick boot being broken can cause lean fuel trims.

Especially check the hard plastic lines going to the brake booster. They'll crack on the backside and won't be obvious.