Cruise Control - Surging
No: 19/O1/04/NASReplaces 19/01/02/NAS
Issue: 1
Date: 28 October 2004
Cruise Control Surge Correction
AFFECTED VEHICLE RANGE:
Discovery Series II (LT) 3A767790 and up equipped with 4.6 liter engine
SITUATION:
CRUISE CONTROL SURGE
2003 and 2004 Model Year 4.6 liter equipped Discovery Series II vehicles have a cruise control software configuration which can result in objectionable "surge" of up to 2-3 mph around the "target" speed. Additionally, an incorrectly adjusted cruise control cable or minor vacuum leaks can contribute to the sensation of "surge" even if target speed is maintained.
RESOLUTION:
VERIFY CABLE SETTING AND INSTALL NEW CRUISE CONTROL CONFIGURATION
If the customer complains of experiencing the surge problem, verify that the cruise control cable setting is correct. Investigate the current state of the cruise control tune and if necessary update following the instructions in this TIB. Installation of the updated cruise control configuration using TestBooklT4 will likely resolve the surge situation in combination with a properly set cable. If the problem persists once the new tune is installed investigate and correct any vacuum system leaks.
PARTS INFORMATION:
Not applicable
DDW WARRANTY CLAIMS:
DDW requires the use of causal part numbers. Labor only claims must show the causal part number with a quantity of zero.
Normal warranty policy and procedures apply.
Material allowance is included in labor operation.
REPAIR PROCEDURE
VERIFY CORRECT TUNE
NOTE:
The Workshop Manual provides a range for cruise throttle adjustment. The middle of that range is the optimum setting and should always be set for the best possible operation of the Cruise Control system.
1. Refer to the GTR Workshop Manual section 19.75.11 and verify that cruise throttle cable is set with maximum 1 mm (0.040 in) gap between the cam and the lever.
2. Connect TestBook/T4 to the vehicle.
3. Insert Testbook/T4 disc Archive 022 or later.
4. Connect Blue diagnostic lead to the vehicle.
5. Turn ignition to position "II".
CAUTION:
Hand brake should be set and the transmission placed in the neutral "N" position.
6. Verify hand brake is set and transmission is in neutral.
7. Depress instrument cluster cruise master switch to place in "on" (switch illuminated) condition.
8. Select "Diagnostic System" on 14 screen.
9. Select "Discovery, 2003MY" on the 14 screen.
10. Enter the vehicle VIN and press "Continue" on the 14 screen.
11. Confirm vehicle info and press "Continue" on the 14 screen.
12. Select "Cruise Control / Petrol / Vehicle Maintenance / View Tune" on the 14 screen.
NOTE:
At this point, T4 will read the tune values from the vehicle and provide a display of those values.
13. Compare the tune values to the values listed.
INSTALL UPDATED TUNE
1. If the vehicle contains different tune values than those listed in the table, select "Cruise Control / Petrol / Vehicle Maintenance / Program ECU / Set new tune 4.0L engine" on the 14 screens.
NOTE:
Download of the tune values from T4 to the vehicle will take only a few seconds.
2. When programming is completed read back the tune values and verify that they match the listing in the table above.
3. End session the diagnostic session and disconnect 14.
NOTE:
The Cruise Control ECU requires some adaption time after programming. Notify the customer that the adaption period should be approximately 10 miles at a speed above 30 mph with cruise engaged.
4. Test-drive the vehicle and verify that the new tune has resolved the issue of cruise surge.
VACUUM SYSTEM LEAK CORRECTION
1. If the surge persists after the test drive, investigate to determine if there are any leaks in the vacuum system and correct using appropriate SRO.
2. Test-drive the vehicle and verify that cruise surge has been corrected.