Checking (for 3 and 4-wire lambda sensors)

Use suitable measuring instruments such as a multimeter (V, A, W measuring instrument) or an engine analyzer.
With new systems the most important values can be recorded with the Bosch testers of the KTS or FSA series using their self-diagnosis function.

 

Notes on trouble-shooting
Take measurements and perform checks before removing the lambda sensor. The engine must be warm.

 

 

Fault lamp check
(OBD: On-board diagnosis)

A defective lambda sensor may cause the OBD lamp to light.

Fault memory read-out

Make use of a tester (for example KTS 520, 540, 550, 570, 650, FSA 740) or the flash code.

Visual inspection
(in situ)

Applicable to connector, wiring and lambda sensor.

Exhaust and intake system
leak test

Pay particular attention to the area between the engine and the lambda sensor. The ingress of additional air will bias the lambda sensor signals.

Wiring check

Check for open circuit, short to positive or short to ground in the wiring.

Test procedure

Connect up diagnostic tester, such as Lambda control tester or engine analyzer.

Lambda sensor check
To be performed if the above trouble-shooting is not successful.

Test items

Action in the event of deviation

Note the following

Measurement of reference voltage
Approximate values:
400...500 mV

Check control unit/electrics

Take measurement at unplugged connector on control unit end.

Measurement of lambda sensor signal frequency
Approximate values at idle:
> 0.5 Hz
   (cycle < 2 sec)

Replace lambda sensor

Plug in connectors. The frequency of the sensor signal voltage increases with increasing engine speed. Use can also be made of a lambda control tester for this purpose.

Measurement of heating resistance
if > 30 ohms

Replace lambda sensor

Take measurement at white wires on sensor end with connector unplugged.

Measurement of heating voltage
Approximate values:
10 – 14.5 V

Check control unit/electrics

Heating voltage measurement is not possible if the lambda sensor heating has been deactivated on attaining the minimum lambda sensor operating temperature.

Measurement of sensor voltage
Approximate values with warm engine:
Rich values > 0.6 V
Lean values < 0.4 V

Replace lambda sensor

Take measurement at black and grey wires (for 4-wire sensors) or at black wire and housing (for 3-wire sensors).

Removal and installation
It is advisable to refer to the vehicle-specific trouble-shooting instructions when working with lambda sensors.

 

 

Assembly tool

Use a 22 mm open box wrench or tool adapter.

Tightening torque

40...60 Nm (use torque wrench).

Renewed installation of sensor

Grease the thread with suitable assembly paste. Attention: Paste must not come into contact with guard tube.

Fitting new sensor

Bosch lambda sensors are supplied with a ready-greased thread and a protective cap. Only remove the protective cap immediately prior to installation.

Fitting instructions

  • Take care not to twist the wiring harness on fitting/screwing in the sensor. Do not tug on the cable and connector.
  • Sensors are not to be used if the connector is dirty or damaged.
  • For the lambda sensor to function properly, it is important to keep the inside of the connector clean. It is therefore essential to protect the connector against all forms of contamination.
  • Use cable ties to take up any excess length of connecting cable. Make into a loop if neccesary.

Important

To protect the lambda sensor

  • Only use unleaded fuel without additives.
  • Have the vehicle serviced at regular intervals.
  • Only provide starting assistance using jumper cables (not "bump" starting), as unburnt fuel could enter the exhaust system if the vehicle were to be pushed.
  • Do not fill the engine with oil beyond the max. mark on the dipstick.
  • Observe checking and replacement intervals: Check the lambda sensor regularly (every 30 000 km) and replace at the intervals recommended by Bosch. The recommended checking and replacement intervals can be found in ESI[tronic], Tecdoc and the corresponding catalogues.