Oxygen Sensor - Codes 44 & 45 Diagnosis
04/11/9419/01/94/US
SUBJECT:
Heated Oxygen Sensor (HO25) Diagnosis - Diagnostic Trouble Codes (DTC) 44 and 45.
MODEL:
Range Rover, Discovery, Defender
AFFECTED VEHICLES
All Range Rover, Discovery and Defender
DETAIL
There has been a high level of unnecessary HO2S sensor replacement when codes 44 and 45 have been experienced. HO2S sensors are extremely reliable and rarely fail. It is even more unlikely that both the sensors will fail simultaneously. Subsequently most of the sensors returned to Land Rover when tested result in "no fault found".
Ensure that the diagnostic help points described are followed before replacing any HO2S sensors.
Note:
Replacement of a sensor that does not have a defect may lead to a warranty debit
ACTION REQUIRED
In the event of HO2S sensor DTC faults 44 and 45 being stored, ensure that the items listed below are completed during diagnosis.
PARTS INFORMATION
Not applicable
PROCEDURE
1) When using Test Book to observe HO2S feedback values, do not assume the sensor is at fault if the reading from either bank is seen to be zero.
If a HO2S DTC 44 or 45 is stored by the ECM, the ECM defaults to a zero fueling correction value on the bank the fault occurred on. If zero is observed as fueling correction from one or both sensors, Clear the stored DTC using Test Book and the structured diagnostics. If the sensor is then seen to switch correctly the fault is elsewhere in the system - it may be intermittent.
2) Microcorrosion on the MAFS sensor terminals can lead to fueling levels being incorrect for the quantity of actual air flowing into the engine. This problem can lead to the HO2S sensor OBD diagnostics being activated and DTC 23, 44 or 45 being flagged. To protect against this problem the MAFS sensor connector should be protected with Lithium grease as described in Service Bulletin P93/19 - 002. Gold plated MAFS terminals were introduced on Discovery RA112195 and Range Rover SA655827 (Defender will be changed at launch of 95 Model Year Defender), DO NOT GREASE GOLD TERMINALS.
3) HO2S sensor connectors; widening of the female terminals inside the connector can lead to poor circuit integrity. To ensure good contact, lightly squeeze the male pins and tweak the female sockets with a pair of needle nose pliers before reassembling.
4) HO2S signal and ground connectors at the 40 way ECM connector (pins 4, 23 and 24).
5) HO2S ground on the end of "A" bank cylinder head - always check with a wrench.
WARRANTY
Normal warranty policy and procedures apply.
COMP CODE: 2T6 or 2T5
SRO
19.22.01.44 - Access OBD code "44" - 00.40 hrs
19.22.01.45 - Access OBD code "45" - 00.40 hrs