Engine-Codes - Mercedes-benz - P0174 MERCEDES-BENZ

P0174 MERCEDES-BENZ - System Too Lean Bank 2

Repair Importance Level: 3/3
Repair Difficulty Level: 3/3  What is this?
Table of contents

P0174 MERCEDES-BENZ Possible Causes

  • Intake air leaks
  • Faulty front heated oxygen sensor
  • Ignition misfiring
  • Faulty fuel injectors
  • Exhaust gas leaks
  • Incorrect fuel pressure
  • Lack of fuel
  • Faulty Mass Air Flow (MAF) sensor
  • Incorrect Positive Crankcase Ventilation (PCV) hose connection

How is the P0174 MERCEDES-BENZ code repair?

Start by checking the "Possible Causes" listed above. Visually inspect the related wiring harness and connectors. Check for damaged components and look for broken, bent, pushed out, or corroded connector's pins.

Tech Notes

Mercedes Benz Code = 0341 Self-adaptation of mixture formation for enrichment at partial load for the left cylinder bank is above the permissible limit. (P0174)

If the P0171 is combined with the P0174 code, it's very likely that the problem is caused by an intake leak. If there are no intake leaks, the next step is to replace the air filter and clean the air flow meter. If the problem persists the front oxygen (O2) sensor may need to be replaced.

What is the cost to diagnose the P0174 MERCEDES-BENZ code

Labor: 1.0

The cost to diagnose the P0174 MERCEDES-BENZ code is 1.0 hour of labor. The auto repair's diagnosis time and labor rates vary by location, vehicle's make and model, and even your engine type. Most auto repair shops charge between $75 and $150 per hour.
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When is the code detected?

- Fuel injection system does not operate properly.
- The amount of mixture ratio compensation is too small. (The mixture ratio is too lean.)

Possible Symptoms

  • Engine Light ON (or Service Engine Soon Warning Light)
  • Excessive Fuel Consumption


This fault code is stored in the Engine Control Module (ECM) when the ECM is no longer capable of controlling the air fuel ratio. For correct operation of the catalytic converter the ECM is required to keep the air fuel ratio (AFR) at approximately lambda 1, this equates to an AFR of 14.7:1 by mass. This is achieved by trimming the fuel mixture to the required amount to cater for slight anomalies during normal operating conditions. However when a fault causes the fuel trim to exceed a predetermined level the malfunction indication light is illuminated and a limited operating strategy is employed. The pre-catalyst exhaust gas oxygen sensor is the primary component used for calculating the fuel trim once the system enters closed loop control. The fuel trim data can be displayed as a percentage, either positive or negative.
Under this condition the fuel trim data will display a positive value. The ECM will increase the injection duration to counteract the excessively lean mixture. This fault can be stored due to an air leak in the induction system, the exhaust system in close proximity to the exhaust gas oxygen sensor, low fuel pressure, faulty fuel injector or a mechanical defect affecting the engine.

More Information

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