P1129

P1129
Fuel Trim System too rich TRA (cylinder 4 - 6)
Oxygen Sensing Adaptation TRA (cylinder 4 - 6) Lean limit

Function
The adaptive oxygen sensing corrects longer lasting deviations of the fuel/air mixture of Lambda = 1 through changes of the calculated monitoring within the Engine Control Module (ECM) and with that the injection time. Should the correction factor through adaptation exceed a predetermined value, the diagnosis will detect the adaptation limit.

Diagnosis condition
- Oxygen sensing active.
- Time elapsed after engine start-up 250 to 350 sec.
- Air mass > 50 Kg/h

NOTE: If DTC P1129 (oxygen sensing at lean limit) is in memory, the fuel/air mixture is too rich. Always read the DTC memory as it is possible that there are other faults stored in memory which may lead the control to run against the limit.





Diagnosis procedure
Connect scan tool and advance to menu point "DTC memory".
1. Connect scan tool with adapter cable.
2. Switch ignition on
3. Start diagnosis and advance to menu point "DTC memory"
4. Read DTC memory.

- If other DTCs are in memory: Read DTC memory, correct fault
- If DTC P1127: Check fuel pressure

Read DTC memory, correct fault
1. Read DTC memory.
2. Correct fault as per Repair Manual.
3. Erase DTC memory.
4. Then road test vehicle to enable the system to monitor all components once.
5. Again read DTC memory.

- If no fault: End
- If DTC P1127: Check fuel pressure





Check fuel pressure
1. Remove cap of test connection at fuel distributor line.

CAUTION: Cap must be used only once!

2. Connect pressure gauge P 378 or VW 1318 to attachment line 9559 and connect to test connection.





3. Remove ECM relay (R53) from fuse/relay panel and connect terminals 30 and 87b with locally manufactured fused jumper cable. The fuel pump should work now.

Fuel pressure:
Engine not running: 3.8 +/- 0.2 bar
Engine at idle: 3.3 +/- 0.2 bar.

- Fuel pressure not OK (too high).: Check fuel pressure regulator

Check fuel pressure regulator, Vacuum connection and fuel return line.
1. Remove vacuum line at fuel pressure regulator and check vacuum with vacuum tester.

Engine at idle: 0.4 - 0.6 bar.

- If the specified value is not reached, check air intake system for leaks and vacuum lines to fuel pressure regulator for restrictions.

2. Check fuel pressure regulator for outside damage.

- If the fuel pressure regulator is damaged and with that the pre-tensioning of the spring is increased, replace the fuel pressure regulator.