Troubleshooting DTC Fault Codes Related To: Adaptation Limits Of Lambda Control, Mass Air Flow Sensor/Intake Air Temperature Sensor (07.61/59A)

General Information: Description of the adaptive mixture control as part of the lambda control:

Fig 1: Adaptive Mixture Control System Diagram

The catalytic after treatment of the exhaust gas using a closed loop three way catalytic converter has proven to be a highly effective means of meeting the current low emission limits.

Approximately 14.7 kg of air are required for complete combustion of 1 kg of gasoline. The excess air factor lambda  is used to define this A/F ratio. The engine must be operated within a very narrow range in which lambda  = 1 +/- 0.005. Such precision can only be achieved with precise closed loop control of the A/F mixture with a lambda oxygen sensor installed upstream of the converter. A second lambda sensor downstream of the catalytic converter increases the precision even further.

To compensate individual engine differences and long-lasting drifts in sensors and actuators of the injection system and also to compensate small not measured air leakage, the lambda control contains an adaptive pilot control. This adaptive pilot control takes over the controller correction in two different ranges (see Fig 2). It takes a certain time of learning in each range, until the correction is completed.

Deviations of the A/F ratio in range 1 is compensated by an additive factor and in range 2 by a multiplying factor. There are individual factors for the right and the left banks of the engine.

For example, if the multiplicative factor (adapted in range 2) at idle speed is too large, the additive factor (adapted in range 1) will adapt in a negative direction.

Example: 

Idle adaptation of 3 % means mixture control at idle is adding fuel. Look for cause of engine is running lean. Partial load adaptation of 0.80 means mixture control at partial load is taking fuel away. Look for cause of engine is running to rich.

Fig 2: A/F Ratio Ranges

Repair process for fault codes from adaptation of mixture formation:

Self-adaptation of mixture formation (right/left bank) for enrichment at partial load is above the permissible limit (fault codes 0337, 0341, 0789, 0793, 1045, 1049, 2089, 2093). 

If this value is greater than 1.20 there may be unmetered air (a leak) in the intake system or not enough fuel is being supplied to the combustion chamber.

• The oxygen sensor measures a lean  signal which causes the lambda control to compensate for the problem by making the mixture richer. 

Fig 3: Repair Process For Fault Codes 0337, 0341, 0789, 0793, 1045, 1049, 2089, 2093

Self-adaptation of mixture formation (right/left bank) for enleanment at partial load is below the permissible limit (fault codes 0338, 0342, 0790, 0794, 1046, 1050, 2090, 2094). 

If this value is less than 0.80 the fuel pressure may be higher than 4 bar (affects both cylinder banks) or a fuel injector is leaking. In this case too much fuel is supplied into the combustion chamber.

The oxygen sensor measures a rich  signal, which causes the lambda control to compensate for the problem by making the mixture more lean. 

Fig 4: Repair Process For Fault Codes 0338, 0342, 0790, 0794, 1046, 1050, 2090, 2094

Self-adaptation of mixture formation (right/left bank) for enrichment at idle speed is above the permissible limit (fault codes 0745, 0749, 1045, 1049, 2091, 2095). 

If the actual value of self-adaptation in the idle speed range is 3 % above the stated set values on both cylinder banks, there may be unmetered air (a leak) in the intake system or the connected vacuum and crank chase ventilation lines. In this case not enough fuel is being supplied into the combustion chamber.

The oxygen sensor measures a lean  signal which causes the lambda control to compensate for the problem by making the mixture richer. 

Fig 5: Repair Process For Fault Codes 0745, 0749, 1045, 1049, 2091, 2095

Self-adaptation of mixture formation (right/left bank) for enleanment at idle speed is below the permissible limit (fault codes 0746, 0750, 1046, 1050, 2092, 2096). 

If the actual value of self-adaptation at the idle speed range is 3 % below the stated set values the fuel pressure may be higher than 4 bar (affects both cylinder banks) or a fuel injector is leaking. In this cases too much fuel is supplied into the combustion chamber.

The oxygen sensor measures a rich  signal, which causes the lambda control to compensate for the problem by making the mixture more lean.

Fig 6: Repair Process For Fault Codes 0746, 0750, 1046, 1050, 2092, 2096

In the case of an adaptation mixture formation fault code on both cylinder banks please check the following: 

• Check seal of component B2/5 (hot film mass air flow sensor). 
• Inspect air filter housing for correct installation. 
  Fig 7: Damaged Seal Between Hot Film Mass Air Flow Sensor And Air Filter Housing

  
  Fig 8: Air Filter Housing

  

  A damaged seal (Fig 7) between the hot film mass air flow sensor and the air filter housing or a improper installation of the air filter housing (Fig 8) can cause a false air flow measurement. The measured value of this improper air flow does not represent the actual air mass. The difference between the measured value (based on the false measurement) and the actual value of the air mass in the engine is corrected by the lambda control. In this case a rich or lean condition on both  cylinder banks can occur.

  NOTE: Please be informed that models 203 and 209 do not have air intake housing mounting clip due to design packaging.
• Check for restriction on air filter inlet (diesel restrictor plate). 
  Fig 9: Air Filter Inlet

  
  Fig 10: Restrictor Plate For Diesel Engine

  

  A further source for a false air flow measurement can be a restriction before the air filter (plastic bag, ...) or in the air filter inlet (Fig 9).

  Fig 10 shows a restrictor plate for a diesel engine. If this restrictor plate is installed in a vehicle with gasoline engine (M272, M273) it causes also a false air flow measurement!

• Inspect hot film mass air flow sensor for correct installation. 
  Fig 11: Incorrect Installation Of Hot Film Mass Air Flow Sensor

  

  Incorrect installation (Fig 11) of the hot film mass air flow sensor (component B2/5) to the intake manifold might be source for two problems:

  • A false air flow measurement (improper air flow at sensor element).
  • Unmetered air (leak) at the intake system (lean running condition on both  cylinder banks).

  In case of improper installation, correct the installation of the hot film mass air flow sensor to the intake manifold (securely place the clips).

  Do NOT  replace the hot film mass air flow sensor!

• In case of "Self adaptation of mixture formation for enrichment is above the permissible limit" check for air leaks in the air intake system and connected hoses. 
  Fig 12: Hoses Connected To Air Intake System

  
  Fig 13: Cracks In Hoses Connected To Air Intake System

  
  Fig 14: Broken Hose Connection

  
  Fig 15: Open Hose Connection

  

  Check for cracks (Fig 13) and open (broken) connection (Fig 14 & Fig 15) on all hoses connected to the intake manifold.

Functional description of the hot film air flow sensor (component B2/5):

Upon engine start, a current is passed through the hot film air flow sensor, heating the sensor element (Fig 16) to a certain constant temperature. As air passes through the sensor, this film is cooled and the sensor determines how much electricity is required to keep the film up to temperature. This enables the sensor to determine how much air (in weight) is passing through the sensor at any given moment. It also recognizes the direction in which the air is flowing it is able to take pulsation and backflows into account. This means that the hot film air flow sensor is able to measure the actual air mass independent of pulsation and backflows. This signal is then sent to the ME9.7 engine control unit which it compares to a preprogrammed map to deliver fuel and ignition spark, taking into account other engine inputs such as engine rpm and temperature. The hot film air flow sensor HFM 6 transmits a frequency (HFM 5 of engine management system ME2.8 transmitted a signal voltage) to the ME9.7 engine control unit.

The integrated deflection bypass of the HFM 6 (Fig 17) increase the robustness against water and particulate contamination and reduce drift over lifetime.

Fig 16: HFM: Measuring Principle

Fig 17: Integrated Deflection Bypass Of The HFM

The air intake temperature sensor is also mounted into the mass air flow sensor (description see Functional description of the air temperature sensor (component B2/5b1)  ).

Repair process for hot film air flow sensor (component B2/5) related fault codes:

Repair process for fault codes 1345, 1346, 1347: 

This fault codes are stored in case of a problem with the cables or the connectors of the hot film mass air flow sensor (component B2/5) or the hot film mass air flow sensor itself. Please use the symptom overview for component B2/5 (hot film mass air flow sensor) to locate the problem.

To check the signals of component B2/5 (Hot film MAF sensor) on vehicles with ME 9.7 - Motor electronics 9.7 there are two guided tests available in DAS: 

1. Check signal of component B2/5 (Hot film MAF sensor) via actual value with engine OFF: 
   Fig 18: DAS Display - Check Signal Of Component B2/5 Via Actual Value With Engine Off

   
2. Check signal of component B2/5 (Hot film MAF sensor) via actual value with engine speed greater than 3500 rpm: 
   Fig 19: DAS Display - Check Signal Of Component B2/5 (Hot Film MAF Sensor) Via Actual Value

   

Repair process for fault codes 1349, 1350, 1351, 1352: 

These fault codes are stored if the measured air mass is implausible compared to the position of the throttle valve actuator. In this case, please check component M16/6 (throttle valve actuator) for proper operation.

Repair process for fault codes 1857, 1858: 

These fault codes are stored if the ratio of the hot film mass air flow sensor signal to the intake manifold pressure is out of range. In this case, please check component B28 (pressure sensor) for proper operation.

Repair process for fault codes 2181, 2182: 

Check for a proper connection of the connector (5-pin) on the hot film mass air flow sensor (component B2/5).

Fig 20: Diagnostic Tree For Hot Film Air Flow Sensor

Fig 21: Symptom Overview For Hot Film Mass Air Flow Sensor

If the status of the relevant actual value is out of range from the specified value and all test requirements were fulfilled, replace the hot film mass air flow sensor (component B2/5) and send this part with the required DAS original printouts (see below) to our Quality Evaluation Center.

Required DAS-printouts for warranty returns: 

• Printout of all  fault codes of the ME 9.7 - Motor electronics 9.7 (Quick test).
• Freeze frame data of all  fault codes stored in the ME 9.7 - Motor electronics 9.7.
• Printouts (Fig 18, Fig 19) of the HFM-SFI signal of component B2/5 (Hot film mass air flow sensor).

Returned hot film mass air flow sensors (component B2/5) without the required information will be debited back to the dealer as of repair date February 20, 2006. 

Functional description of the air temperature sensor (component B2/5b1):

The air temperature sensor (component B2/5b1) is integrated into the hot film mass air flow sensor (component B2/5). It contains a temperature dependent resistor whose resistance falls with rising temperature. The engine management system (ME9.7 - Motor electronics 9.7) uses the change in the applied voltage in order to determine the air temperature.

Repair process for air temperature sensor (component B2/5b1) related fault codes:

Repair process for fault code 2025, 2026: 

These fault codes are stored in case of a problem with the cables or the connectors of the intake air temperature sensor (B2/5b1).

Fig 22: Diagnostic Tree For Fault Code 2025

Fig 23: Diagnostic Tree For Fault Code 2026

Repair process for fault code 2029, 2030, 2032: 

These fault codes are stored if the measured value of the intake air temperature sensor (component B2/5b1) is implausible.

Fig 24: Repair Process For Fault Code 2029, 2030, 2032

During the plausibility of intake air temperature procedure the actual value of intake air temperature (component B2/5b1) and coolant temperature (component B11/4) is compared at engine cold start. A fault code will be stored when these two temperature values are not close enough to each other. Please check component B11/4 (coolant temperature sensor) for proper operation.

Fig 25: Diagnostic Tree For Coolant Temperature Sensor

If the measured value of the resistor of the intake air temperature sensor (component B2/5b1) is out of range from the specified value and all test requirements were fulfilled, replace the hot film mass air flow sensor (component B2/5) and send the part with the required DAS-printouts (see next page) to our Quality Evaluation Center.

Required DAS-printouts for warranty returns:

• Printout of all  fault codes of the ME 9.7 - Motor electronics 9.7 (Quick test).
• Freeze frame data of all  fault codes stored in the ME 9.7 - Motor electronics 9.7.

Returned hot film mass air flow sensor (component B2/5) without the required information will be debited back to the dealer as of repair date February 20, 2006. 

Repair process for fault codes of adaptation of mixture formation - Diagnostic trees of related systems and components:

The main diagnostic tree for adaptation of mixture formation links to several related systems and components. For a complete diagnostic solution it may be necessary to follow the diagnostic path of a linked diagnostic tree.

Fig 26: Diagnostic Tree For Lambda Control

Fig 27: Diagnostic Tree For Fuel System (Lean Condition) - "Fuel Restriction"

Fig 28: Diagnostic Tree For Fuel System (Rich Condition) - "Too Much Fuel"

Fig 29: Diagnostic Tree For Fuel Injectors

Fig 30: Performing Self-Adaptation Of Mixture Formation