P1123,P1124, P1127, P1128

Symptom: CHECK ENGINE LAMP (MIL) on. Poorer driveability, hunting idle speed. Possibly also other diagnostic trouble codes, e.g. low fuel level, mass air flow sensor, misfiring.

P1123 , P1124 , P1127 , P1128

Fault symptoms

CHECK ENGINE LAMP (MIL) on. Poorer driveability, hunting idle speed. Possibly also other diagnostic trouble codes, e.g. low fuel level, mass air flow sensor, misfiring.

Conditions

P1123 Additive adaptation < 0.5 ms.

P1124 Additive adaptation > 0.5 ms.

P1127 Multiplicative adaptation < -24%%.

P1128 Multiplicative adaptation > 22%%.

Diagnostic help

An adaptation reading can be obtained with the ISAT scan tool.

-	Select "READ FUNCTIONS".

-	Select "ADDITIVE ADAPTION".

-	Select "MULTIPL ADAPTION".

Current multiplicative adaptation is show as a percentage (±25 %%). Current additive adaptation is show in ms (±0.512 ms).

Check the wiring

Intermittent faults may occur as a result of temporary short circuits and breaks in the wiring. Jiggle the wiring at several points and in different directions to ascertain whether the wiring harness, including any connectors, is causing the trouble. Observe the multimeter, ISAT scan tool or test lamp while doing this.

Diagnostic procedure

1. Check other diagnostic trouble codes in the Motronic system

-	Use an ISAT scan tool to obtain readouts of all diagnostic trouble codes.

Does the ISAT scan tool show additional diagnostic trouble codes?

yes

Continue fault diagnosis as described for the relevant diagnostic trouble code. Continue with point 5.

no

Continue with point 2.

2. Check for air leakage in the intake system

-	Check that no air leakage occurs in the intake system after the mass air flow sensor. Carefully inspect all vacuum hoses and the crankcase breather hose. Inspect the two O-rings in the intake silencer.

-	Check all systems that are connected to the intake system.

-	Check that the EVAP canister purge valve does not leak under zero current conditions.

Is the intake system OK?

yes

Continue with point 3.

no

Rectify the fault. Continue with point 5.

3. Check the performance of the mass air flow sensor

-	Connect the ISAT Scan Tool.

-	Start the engine.

-	Turn off the A/C and all electrical equipment.

-	Select "READ FUNCTIONS".

-	Select "MASS AIR FLOW SENSOR".

Check that the ISAT scan tool shows the following air mass as a function of engine rpm:

•	idling speed . . . . . . . . . . . . . . . . . . . . . . . . about 1.0 V

•	at 2500 rpm (no load) . . . . . . . . . . . . . . about 1.5 V

Slightly higher values will be obtained with a cold engine.

Are all readings OK?

yes

Continue with point 4.

no

Change the mass air flow sensor. Continue with point 5.

4. Other checks

-	Check that:

Checks OK?

yes

Continue with point 5.

no

Rectify the fault. Continue with point 5.

5. Final check

-	Connect the ISAT Scan Tool.

-	Start the engine and run it at idling speed until the temperature of the coolant has attained 60°C (140°F).

-	Switch off the engine, restart it and run it at idling speed until the EVAP canister purge valve stops working (about 90 seconds).

-	Read "MULTIPL. ADAPTION" during the time the EVAP canister purge valve is not working (about 80 seconds).

Does the ISAT scan tool show >+15%% or <-15%%?

yes

Continue as described in .

no

The steps taken to rectify the fault were correct.