AA/MKG X XXX XXX XXX/201008 64.64.XX
Bosch Tips
Systematic Testing of
Lambda Sensors
How to detect faulty lambda sensors
Information on testing:
Failure causes:
Symptoms:
Possible consequences:
For detailed test procedures
and test specifications refer to
ESI[tronic].
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 Defective catalytic converter
 Engine bearing damage due to
rough running
Electrical faults
Mechanical damage
Poisoning/contamination
Thermal overload
Malfunction indicator lamp
(MIL) on
Driveability problems
Unstable idling
Increased fuel consumption
Increased exhaust emissions
Test steps
Testing the lambda sensor heater
Possible causes:
 Relay not switching through
"continuous positive"
 No switched ground connection
from ECU
 Wire break, short to ground or
short to positive
Testing the lambda sensor signal
Check power supply to lambda sensor
heater.
No
Test requirements:
 Injection system OK
 Intake system and exhaust tract leak-tight
 Engine warmed-up and idling
Power supply OK?
Yes
Lambda sensor
Check heater resistor at ambient
temperature.
Lambda sensor defective
No
Check signal profile
Switching lambda sensor:
 Signal swings between approx. 0.1 ...0.9 V
 The greater the voltage excursion, the better the signal
 Frequency between 0.5 ...3 Hz
 Voltage below 0.4 V ➔ lean mixture
 Voltage above 0.5 V ➔ rich mixture
Test specifications OK?
See ESI[tronic]
Yes
Wideband lambda sensor:
 With lambda = 1 ➔ pump current approx. 0 mA
 Pump current below 0 mA ➔ rich mixture
 Pump current above 0 mA ➔ lean mixture
Warm-up engine.
Measure heating current.
Lambda sensor defective
No
Does the heating current fall as the
temperature rises?
Lambda sensor defective
No
Signal profile OK?
Yes
Yes
Wiring harness
Check vehicle wiring harness for:
 Damage
 Corrosion damage
 Contacting faults on the connectors
 Open circuit, continuity, short to
ground, short to positive and contact
resistances
Repair/replace wiring harness
Yes
Cause(s) found?
Check vehicle wiring harness for:
 Damage
 Corrosion damage
 Contacting faults on the connectors
 Open circuit, continuity, short to ground,
short to positive and contact resistances
Repair/replace wiring harness
Yes
Cause(s) found?
No
No
Control unit with connector strip
Check control unit:
 Is the reference voltage OK?
 Check connector strip for damage,
corrosion and contacting faults
Control unit defective.
Yes
Cause(s) found?
Check control unit:
 Is the reference voltage OK?
 Check connector strip for damage,
corrosion and contacting faults
Control unit defective.
No
Lambda sensor heater OK.
Clear fault memory, run test drive,
check fault memory.
Yes
Cause(s) found?
No
Lambda sensor signal OK
Clear fault memory, run test drive,
check fault memory.