Lotus 2004 Eleven Service Notes page 171

Lotus Service Notes
Catalyst System Efficiency
P0420 Catalyst System Efficiency Below Threshold
Description
The ECU compares the waveform of the oxygen sensors located before and after the catalyst to determine
whether or not the catalyst has deteriorated. If the catalyst is functioning normally the front oxygen sensor will
be switching between rich and lean whilst the rear oxygen sensor should also be switching between rich and
lean but more slowly. When both the oxygen sensor waveforms change at the same rate, it indicates that the
catalyst performance has deteriorated. The ECU counts the number of pre and post catalyst oxygen sensor
switches and divides one by the other to determine a ratio number. If the ratio number is greater than 0.6 ('06
M.Y.; 0.165) the code is set.
Sensor connections
Pre catalyst oxygen sensor
Sensor Connector
1
2
3
4
Post catalyst oxygen sensor
Sensor Connector
1
2
3
4
Malfunction Criteria
• Closed loop fuel control enabled
• Coolant temperature > 60 °C (140 °F)
• Baro > 756 mbar
• Vehicle speed < 130 km/h (81 mph)
• MAF < 40 g/sec
• Air inlet temp > -10°C (14°F)
Disable Criteria:
P0101, P0102, P0103
P0107, P0108
P0116, P0117, P0118
P0131, P0132, P0133, P0134, P0135, P0137, P0138, P0139, P0140, P0141 – Oxygen sensor faults
P0171, P0172
P0300, P0301, P0302, P0303, P0304
Potential failure modes:
• Exhaust system leak
• Oxygen sensor faults
• Oxygen sensor heater failure
• Catalyst failure
Notes:
• The MIL will be illuminated if the fault is present for 2 consecutive trips.
• Further information on the sensor may be found inToyota 1ZZ-FE, 2ZZ-GE manual RM733E (B120T0327J)
pages DI-86 to DI-88
Page 28
Description
Signal
Ground
Heater Supply
Battery Voltage
Description
Signal
Ground
Heater Supply
Battery Voltage
P0420
ECU Pin ECU Connector
15 (A3) 52 Way (Left)
41 (F4) 52 Way (Left)
1 (K3) 52 Way (Left)
- -
ECU Pin ECU Connector
3 (B3) 52 Way (Left)
29 (F4) 52 Way (Left)
27 (H3) 52 Way (Left)
- -
Section EMP
'06 M.Y. in brackets
'06 M.Y. in brackets
– MAF faults
– MAP / Baro Faults
– Coolant temperature faults
– Fuelling faults
– Misfire faults