Pre-HE Engine Sensors

Hi All,

I’m having trouble identifying all the coolant sensors on my 1977 Pre- HE XJ-S

I’ve attached pictures below

A bank:
#2 is cold start, thermo-time switch?

Does anyone know what some of these are? What values they should read?

I’ve been able to find values to test the Air temperature sensor.


Does anyone know what some of these are? What values they should read?


I don’t have any answers for you on those items but…I am assembling a list of pre-HE V12 owners as they are getting to be a rare breed. Ha…yea, the cars and the owners. If I can add you to my list…go to my website Look for my e-mail link, and send me your info. I just two weeks ago had a customer ask the same info as in your post. Tks.
SD Faircloth

Hey SD,

Just sent you an email.


Hi Zak

You are correct, #2 on A-bank/first picture is thermotime. This controls the cold start injectors. Note: these are an unimportant component of the D-Jetronic system and the car should function just fine without them.

On B-bank, I think the item labelled “L.S.” is a vacuum valve which controls the air pump and exhaust gas recirculation system. I suspect that if you poke around beneath the cloth wrapping, you may find two small vacuum lines rather than electrical connections. I could be wrong though: a clearer photo of the connections would clarify things.

FWIW, all D-Jetronic connectors on the car are identical. The ones on the temperature sensors in your photos are the same as the ones on the injectors themselves. Therefore, if your mystery item has D-Jetronic electrical connectors, that’s a pretty good indication it’s EFI related.

Conversely, if it has spade terminals or vacuum hoses, that will be a pretty good indicator that it’s a non-EFI sensor (can’t think what that would be) or vacuum (emissions control system, or to attach to fuel pressure regulators to prevent vapour lock at hot start-up)

In terms of the testing values, try this site: D-Jetronic chapter 13: Troubleshooting and repair

Good luck!


1979 XJ 5.3 (pre-HE)