A/C - Revised ECU Diagnosis/Service
No: 80/01/98/NASRef: WSM Sections 80, 76,19
*Issue: 2*
Date: 03/06/98
PRIDE VI 6-40
HVAC - Revised Service Procedures
AFFECTED VEHICLE RANGE:
RANGE ROVER (LP) Up to WA381431
* indicates updated information
SITUATION:
REVISED DIAGNOSTIC AND PARTS POLICY FOR NEW HVAC ECU
At VIN WA381431 the HVAC ambient temperature sensor was moved from the fresh air intake plenum to a new location behind the front spoiler. The revised location greatly improves the response time of the sensor. At the same VIN, the software in the HVAC ECU was changed to allow it to properly interpret the signal from the relocated sensor.
The revised ECU employs a software strategy that prevents engine heat soak from affecting the temperature reading at low vehicle speeds. Under certain conditions, this strategy may prevent the display from updating. A revised procedure for diagnosing ambient temperature is required to prevent unnecessary replacement of the ECU.
The older HVAC ECU will be superceded to the latest style. When an ECU is replaced on an older vehicle, the sensor will need to be relocated in order for the system to operate correctly.
RESOLUTION:
REVISED DIAGNOSTIC AND PARTS POLICY
Different diagnostic procedures are required to service the HVAC system. Use the procedure outlined in this TIB to diagnose ambient temperature sensor faults on vehicles with externally mounted temperature sensors.
When replacing the HVAC ECU for any reason on a vehicle before WA381431 reposition the ambient temperature sensor using the procedure in this TIB.
*NOTE:
The repairs outlined in this TIB are to be performed to resolve customer complaint of the symptoms described.*
PARTS INFORMATION:
JTN100000 ECU Installation Kit (supercedes AWR5051)
WARRANTY CLAIMS:
82.20.89.28 Time 1.30 hrs.
Install replacement HVAC ECU and install external temperature sensor
FAULT CODE: U
Normal warranty policy and procedures apply
REPAIR PROCEDURE:
REVISED AMBIENT TEMPERATURE SENSOR DIAGNOSIS PROCEDURE
NOTE:
On vehicles with an exterior mounted ambient temperature sensor the following operational parameters must be kept in mind when troubleshooting the system:
^ Under most conditions the ambient temperature display does NOT update until the vehicle is driven over 15 MPH (25 KPH). THIS IS NORMAL AND DOES NOT INDICATE A FAULT WITH THE CONTROL UNIT.
^ If the temperature reading is increasing, the ECU will limit the temperature change to a rate of 1°F (0.5°C) per minute.
1. To diagnose an inaccurate temperature indication, first drive the vehicle above 15 MPH (25 KPH) for several minutes to determine if the temperature reading adjusts to current conditions.
2. If the reading is still incorrect, check the resistance of the temperature sensor and compare it to the resistance values in chart.
3. If the sensor resistance is as specified, disconnect connectors C245 and C250.
NOTE:
In each of the following checks, if the resistance exceeds 2 ohms it is considered excessive.
4. Perform a resistance check of the sensor wires as follows:
^ Check resistance between C245, terminal 8 and C250, terminal 1
^ Check resistance between C245, terminal 7 and C250, terminal 2
5. Repair any leads where the resistance exceeds 2 ohms and repeat the resistance check.
NOTE:
In each of the following checks, the resistance reading must be infinite.
6. With C245 and C250 disconnected, check the sensor wires for a short:
^ Check resistance between C245, terminal 8 and ground
^ Check resistance between C245, terminal 7 and ground
^ Check resistance between C245, terminal 7 and C245, terminal 8
7. Repair any leads that have continuity in the above steps and repeat resistance and continuity checks.
8. Install connectors C245 and C250 when repairs are complete.
SYSTEM UPDATE TO LATEST CONFIGURATION ECU
CAUTION:
If the ECU is not matched to the proper sensor configuration, the HVAC system will not operate correctly.
NOTE:
The HVAC ECU has been superceded by the latest version, which is designed to work with an externally mounted ambient temperature sensor. When replacing an older style ECU, the temperature sensor must be relocated to the outside of the vehicle. To facilitate this, the older ECU supercedes to a kit, which consists of an ECU, sensor, bracket and link lead.
NOTE:
The ECU type can be identified by checking the part number on the label:
^ P/N AWR5050 or AWR1012 must be used with an internal temperature sensor located in the air intake plenum.
^ P/N JFC101890 must be used with an external temperature sensor located behind the front spoiler.
SENSOR INSTALLATION
1. Disconnect battery.
2. Remove HVAC ECU as described in Workshop Manual Section 80, Operation 80.10.02.
3. Remove front bumper as outlined in Workshop Manual Section 76, Operation 76.22.72 through step 6.
4. Mark the position of the left bumper impact can assembly relative to the chassis to ensure correct positioning upon installation.
5. Remove the 2 nuts securing the impact can and the washer plate behind the nuts.
6. Install the bracket supplied in the kit in place of the washer plate with the sensor mounting opening in the down position (Figure 1).
7. Install bumper mount nuts, position the impact can to align the position marked in step 4 and tighten the nuts to 25 Nm (18 lbf. ft.).
8. Install the supplied sensor into the bracket opening with the sensor oriented downward and the wire connector upward (Figure 2).
TEMPERATURE SENSOR LINK LEAD INSTALLATION
1. Connect the supplied link lead to the ambient temperature sensor.
2. Route the lead into the engine compartment by following the path of the left fog lamp wire.
3. Secure the temperature sensor link lead to the existing fog lamp wire with electrical tape.
4. Prepare engine compartment for routing the link lead as follows:
^ Remove cruise control vacuum control unit as outlined in Workshop Manual, Section 19, Operation 19.75.06.
^ Remove EVAP canister as outlined in Workshop Manual, Section 17, Operation 17.15.13.
^ Pull firewall NVH pad aside to expose the grommet shown in Figure 3.
5. Route link lead along the left side of engine compartment to the firewall grommet.
6. Secure lead by taping it to the existing harness.
7. Remove tape on firewall grommet.
8. Feed link lead into vehicle.
9. Apply new tape to grommet.
10. Remove driver's side fascia closure panel as outlined in Workshop Manual, Section 76, Operation 76.46.27.
11. Within the fascia, route the link lead to the HVAC ECU opening as shown in Figure 4. Secure link lead to harness with electrical tape.
12. Connect the link lead to HVAC ECU connector C245 as shown.
NOTE:
Do not remove the temperature sensor in the intake HVAC plenum. Doing so would introduce air leaks into the vehicle.
13. Tape back wires removed from HVAC ECU connector pins 7 and 8.
14. Install new HVAC ECU as described in Workshop Manual, Section 80, Operation 80.10.02.
15. Connect battery and test system operation.
16. Install front bumper as outlined in Workshop Manual, Section 76, Operation 76.22.72.
17. Install EVAP canister as outlined in Workshop Manual Section 17, Operation 17.15.13.
18. Install cruise control vacuum control unit as outlined in Workshop Manual, Section 19, Operation 19.75.06.
19. Install driver's side fascia closure panel as outlined in Workshop Manual section 76, operation 76.46.27.