Fuel temperature sensor A circuit high input

reeflodge · **Joined:** Fri Apr 25, 2014 12:35 pm **Posts:** 101

I have just changed the Fuel filter on my 2005 Jeep liberty 2.8CRD and now the engine check light has come on!

The code refers to:- Fuel temperature sensor A circuit high input

What does this mean and how can I fix it?

All the connectors are fitted and everything was put back as it was.

I tried to cancel the Engine Check light but it keeps coming back on!

gmctd · **Posted:** Fri Nov 21, 2014 1:00 pm

Fuel Temp Sensor is the 2-wire plug on engine-side of your fuel filter head - moving it around while changing the filter cartridge prolly disturbed the connection
- unplug the connector, see if the pins in the head are straight, then plug it back in, see if that cures the symptom
- if not, likely the resistive sensor element has opened, requiring replacement of fuel head

See if the 3-wire FUEL HEATER connector, adjacent on the power-brake side, is leaking Diesel Fuel

Even if not leaking, should consider upgrading the complete filter head unit to the new improved version due to fire hazard when heater connection begins leaking fuel, as it will, sooner or later

reeflodge · **Joined:** Fri Apr 25, 2014 12:35 pm **Posts:** 101

Thanks will check in the morning.
Do you know what the Part Number is for the new improved filter head?

gmctd · **Posted:** Fri Nov 21, 2014 1:12 pm

68043089AA is the kit, incl improved connector harness section which must be spliced in by cutting the wires to the oem connector

papaindigo · **Posted:** Fri Nov 21, 2014 1:39 pm

68043089AA is the new filter head with a new filter and water in fuel sensor installed. 68043086AA is the separate required wiring harness. I've seen a few comments from folks getting the wiring with the filter head but based on my personal experience don't count on it unless you specifically confirm that you are getting both.

FYI the wiring pack contains 2 sets for color code wires, don't ask me why the duplication, and no instructions. Check the wiring on your existing heater element plug; match the new wiring based on close size match not color; slid the new wires into the front/plug side of the plug; slip on the blue wiring retainer; undo battery; clip old heater element wires; splice in new wires (I used marine grade butt connectors with heat shrink tubing; plug in; reattach battery.

reeflodge · **Joined:** Fri Apr 25, 2014 12:35 pm **Posts:** 101

I don't really want to replace the whole Fuel Filter head as they are quite expensive over here in the UK.

Is it possible to just changed this sensor for a new one?
I have noticed that it in clipped in so it must be removable but I cant seem to find a part number or a replacement on the net.

gmctd · **Posted:** Sat Nov 22, 2014 7:02 pm

Unless you can see specific damage to the wiring or\and connector, DTC must be due to failed sensor which is internal to the head - it is not serviced separately, nor is the fuel heater element serviced separately

You can find the complete upgrade kits on eBay for ~ $100USD - they will usually be listed by an authorized DCJ dealer

CATCRD · **Posted:** Sat Nov 22, 2014 7:23 pm

reeflodge wrote:

I don't really want to replace the whole Fuel Filter head as they are quite expensive over here in the UK.

Is it possible to just changed this sensor for a new one?
I have noticed that it in clipped in so it must be removable but I cant seem to find a part number or a replacement on the net.

Try just unplugging the fuel temp sensor plug and sticking a 2,000 ohm resistor into the plug. That will fool the ECM into believing the fuel is always about 80ºF. 3kohm will give 60ºF. Your choice, but if it works, would cost almost nothing.

gmctd · **Posted:** Sat Nov 22, 2014 8:27 pm

Choose wisley, pilgrim...............

The Fuel Temperature Sensor alerts the ECM that the fuel coming from the tank is too hot to be useable - ECM then commands the FQS solenoid valve in the CP3 to reduce fuel into the hi-pressure chamber, reducing the volume of flow into the rail, reducing hot return-fuel volume back to the tank, thus giving the tanked-fuel time to cool down

Possibly, not too much worry in winter climes, but forgetting this unwise "mod" in summer climes could be very expensive, having fooled ECM into assuming all is copasetic......................

This is completely isolated from Fuel Heater temperature control, which has it's own designed-in warden to oversee conditions

CATCRD · **Posted:** Sat Nov 22, 2014 10:01 pm

Would not eeeeven worry about that in the UK. Ever been scalded by your fuel tank? Didn't think so.

gmctd · **Posted:** Sun Nov 23, 2014 1:48 am

Alas, the young and feckless........again

>>>

My FTS is connected and functional - it's part of the big HD Cummins fuel manager installed in my KJ

Wasn't too long ago that people were burned at the stake for ignorance - in this case, ignoring thermal expansion

Big difference in being splashed with 180* Diesel fuel and 180* water - Diesel fuel doesn't easily evaporate, water does

Not a matter of being scalded, tho - is a matter of fuel being too hot for the micro-clearances in the hi-pressure plunger\bore fitments x 3 in 30,000psi CP3 injection pump - similar clearances in 30,000psi injectors

Even the old mechanical P7800's could gall and sieze at only 1800psi......................

Then there's the difficulty in efficiently metering fuel within too broad of a temperature span

reeflodge · **Joined:** Fri Apr 25, 2014 12:35 pm **Posts:** 101

gmctd wrote:

See if the 3-wire FUEL HEATER connector, adjacent on the power-brake side, is leaking Diesel Fuel

I have just checked the 2 connectors and neither of them have 3 wires going to them they both only have 2!
No Leaks

The P/N on my fuel filter head is 52129237AA

papaindigo · **Posted:** Sun Nov 23, 2014 12:12 pm

Forget counting wires. When viewed from the front the right plug is the heater element and the left plug is the fuel temperature sensor and their function is discussed at viewtopic.php?f=5&t=22803.

Based on your filter head PN it's a 1st gen filter head and IMHO needs to be replaced simply as a proactive preventative maintenance item due to the rather common failure, which causes air and fuel leaks, of the heater element. See my previous posts with the applicable 2n gen head PNs. The new filter head will come with a new filter and WIF sensor installed but if your current filter is relatively new then swap them. As I understand it the "sensor" part of the fuel temp sensor is inside the fuel filter head assembly so if the problem is in there replacing the head, which you need to do anyway, will cure the problem. If not you need to start looking at wiring issues.

CATCRD · **Posted:** Sun Nov 23, 2014 6:35 pm

gmctd wrote:

Alas, the young and feckless........again

>>>

My FTS is connected and functional - it's part of the big HD Cummins fuel manager installed in my KJ

Wasn't too long ago that people were burned at the stake for ignorance - in this case, ignoring thermal expansion

Big difference in being splashed with 180* Diesel fuel and 180* water - Diesel fuel doesn't easily evaporate, water does

Not a matter of being scalded, tho - is a matter of fuel being too hot for the micro-clearances in the hi-pressure plunger\bore fitments x 3 in 30,000psi CP3 injection pump - similar clearances in 30,000psi injectors

Even the old mechanical P7800's could gall and sieze at only 1800psi......................

Then there's the difficulty in efficiently metering fuel within too broad of a temperature span

His whole question came down to how to avoid shelling out for a new fuel head. I told him.
Thermal expansion of fuel doesn't enter into it. You're looking at a couple %. And without an air fuel ratio to maintain, who cares?
If I were pulling a trailer through an Arizona summer and let the fuel tank run down to 1/8, I'd worry about fuel temp. Otherwise not.

gmctd · **Posted:** Sun Nov 23, 2014 11:02 pm

Ah...and my input was to alert any to the danger of defeating the FTS, a specific safety feature in the BOSCH CP3 CRD Diesel fuel injection system

This is why defeating the oem Fuel Heater is advised

Also, FYI, since noone has commented, 'the young and the feckless' is word play referenced to the old long-running soap opera
"The Hung and the Listless"..........er sumthin like thet....................

reeflodge · **Joined:** Fri Apr 25, 2014 12:35 pm **Posts:** 101

Ok I have just ordered a new Fuel/Water Separator (Fuel Filter Head) P/N 68043089AA but I ordered it from the US
as it was half the price only £88 and that includes the Shipping and Import Duty!
(bit expensive for my Clumsiness when I was fitting the new filter though!)

I dont mind waiting a couple of weeks as its not the Heater leaky connection, it the Temp Sensor that is the problem so its safe to keep driving until it arrives.

I dont think it will include the Wiring Kit P/N 68043086AA but I can get one in the UK for about £10.

All I need to know now is, is it easy to do the modification?

Does anyone have a walkthrough for this or a Video?

papaindigo · **Posted:** Mon Nov 24, 2014 8:07 am

see viewtopic.php?f=5&t=80698&p=850017&hilit=filter#p850017 on wiring. Otherwise to remove old filter head - unplug fuel heater and temp sensor wires; undo fuel hose clamps; push fuel hoses off (don't pull they just grab tighter); undo 2 bolts holding head to mounting plate; lift up assembly and unplug WIF sensor wire; follow wiring instructions; reverse process to install new filter head.

reeflodge · **Joined:** Fri Apr 25, 2014 12:35 pm **Posts:** 101

Thanks

Seems simple enough!
I'll probably splice the wires together with solder then cover with heatshrink.

reeflodge · **Joined:** Fri Apr 25, 2014 12:35 pm **Posts:** 101

Update

New Filter head arrived from the States (half price even with the shipping) now fitted and connector mod done.
All working fine and Engine Check light reset and no longer coming on.

Result

Fuel temperature sensor A circuit high input

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