D1 - 5spd - Interesting Speedometer/CC Question

_ExpeditionMan

Well-known member
Dec 11, 2017
295
34
Texas
All,

1996 D1 5spd - I have two issues which, according to my read of the electrical diagram for NAS Manual trucks, are most likely related. My cruise control is not working and neither is my speedometer. It is important to note that my odometer is functioning correctly. While troubleshooting the cruise control using this guide I was able to confirm that vehicle speed sensor does read near zero at stop and bounce upwards to 8-12 volts when driving. Thus I suspect my VSS is functioning correctly. The only test from the guide that failed was the secondary voltage test and I believe the NAS Manual trucks use a slightly different system than the auto trucks (not a lockout relay) per the RAVE.

So in summary:
-Odometer functions correctly
-Instrument panel fuse is good
-UltraGauge reads speed with no issues
-No driveability issues (idle, stuttering, exc.)
-Tests according to guide above pass, except secondary voltage test (which may not be applicable for NAS Manual)

Am I looking at a hardware failure of the speedometer itself? Am I misreading the RAVE electrical diagram and I have a bad lockout relay preventing my CC from actuating? I thought the speedometer was basically just a meter looking at the voltage reading supplied from the VSS, am I incorrect here?

Thanks,

Jonathon
 

Doug C

Well-known member
Jul 28, 2006
500
2
Central, Virginia
The VDO cruise control units in d1's are known to be a high failure item. The fix is to splice in the connector and control unit from a d2.
 
Jun 25, 2018
7
0
Seattle
Not sure what VDO means, but he's referring to the cruise control electronic control module, ECU (lives behind the glove box). I went through the same writeup fixing my cruise control, and it turned out my ECU went bad.


Check out this link: https://landroverforums.com/forum/discovery-i-39/retrofit-d2-p38-cruise-control-ecu-57040/



Find yourself a cruise control ECU from a D2, preferably one that came with the 4.0, not 4.6 (the ECUs were tuned differently). Wire up the pigtail from the D2 to the D1.