12BD51

12BD51 - P3020

Information saved in
DME

Fault code
12BD51 - P3020

Fault text
Oxygen sensor before catalytic converter, pump current line:
signal voltage in overrun mode too low due to open pump
current line

Fault description
The diagnostic function monitors the voltage of the oxygen
sensor before the catalytic converter.

Condition for fault identification
Test condition:
The fault is recognized when an electrical malfunction is
present in the oxygen sensor before the catalytic converter.
Potential problem source(s):
- Defective wiring harness
- Oxygen sensor before catalytic converter defective
- Defective DME
Terminal condition: none
Voltage condition:
- Onboard electrical system voltage between 9 V and 16 V
Temperature condition:
- Engine warmed to normal temp, above 80 °C
Time condition:
- Overrun operation must be present for at least 3 seconds
and the EGR valve must be closed.
Other conditions:
- Engine on
- Vehicle underway
- Pre-catalyst oxygen sensor heated to adequate temperature
- Overrun mode

Condition for fault memory entry
This fault is logged in the control module's fault memory
immediately.

Action in service
- Check wiring harness between pre-catalyst oxygen sensor
and DME
- Replace pre-catalyst oxygen sensor
- Replace DME

Fault effect and breakdown warning
Breakdown notice:
Continued driving is possible, but because the oxygen
sensor is not ready for closed-loop control, conversion of
exhaust gases in the catalytic converter will be seriously
impaired.
Possible apparent symptoms:
- MIL lamp lights up after 2nd driving cycle
- Higher exhaust emissions
- Higher fuel consumption
- Surge

Driver information
Warning light:
- ECE emissions warning lamp: on
- ECE electronic engine power reduction: on
- CC message: on
- US emissions warning lamp: off
- US electronic engine power reduction: off
- CC message: none

Service instruction
None