Over­heat­ing warn­ing

Car Mechanics (UK) - - Help! -

I have a fam­ily mem­ber who has a 2006 Jaguar X-TYPE with the Ford 2.5 V6 en­gine. They had a prob­lem about a year ago where the coolant tem­per­a­ture gauge would sud­denly shoot up from half­way to red and a red warn­ing light would come on, in­di­cat­ing that it was over­heat­ing. They took it to a garage, which di­ag­nosed a faulty coolant tem­per­a­ture sen­sor, which was re­placed. The car was fine for a few weeks, then the same thing hap­pened again and has re­curred about once every cou­ple of months since.

When the light comes on, they pull over and check un­der the bon­net, but there is no over­heat­ing or bub­bling in the coolant bot­tle and there are no drive­abil­ity is­sues. One of the times the red over­heat­ing light was on af­ter the car was parked overnight, sug­gest­ing the car was giv­ing a false read­ing. A code reader found the code ‘P0116’, in­di­cat­ing the CTS. I deleted the code and ran the car up to tem­per­a­ture and the code didn’t re­turn. On live data, the coolant tem­per­a­ture goes up to around 96°C un­til the fans kick in.

Read­ing through var­i­ous fo­rums on the in­ter­net, peo­ple sug­gest it’s a faulty ther­mo­stat, which seems to be a com­mon prob­lem. Other peo­ple say that there are two coolant tem­per­a­ture sen­sors on the

2.5, but no one seems to know where they’re lo­cated. Would you agree that re­plac­ing the ther­mo­stat and other CTS is the next step? Or do you know of any other com­mon prob­lem? Also, do you have any info of where the sec­ond CTS is lo­cated? Daniel Clark Nei­ther Au­to­data nor the Jaguar Tech­ni­cal In­for­ma­tion Sys­tem have any in­for­ma­tion on a sec­ond coolant tem­per­a­ture sen­sor, and I be­lieve that some peo­ple may be get­ting con­fused be­cause some 2.5 V6 en­gines had a cylin­der block heater unit.

As the light was il­lu­mi­nated at startup on one oc­ca­sion, and as the cool­ing fan ap­pears to op­er­ate cor­rectly with no signs of boil­ing or over­heat­ing, I doubt that the ther­mo­stat is the source of the prob­lem. I would look for a pos­si­ble elec­tri­cal fault in the sys­tem. The full de­scrip­tion of the ‘P0116’ code is ‘En­gine coolant tem­per­a­ture (ECT) sen­sor – range/per­for­mance prob­lem’. This code ap­pears if the en­gine con­trol unit de­tects ei­ther a slow or rapid change in the coolant tem­per­a­ture which does not match the read­ings given by the air in­take tem­per­a­ture sen­sor (IAT). The vari­a­tion in read­ing which is suf­fi­cient to trig­ger the code is built into the ECU as an al­go­rithm and it is pos­si­ble that, when a warm en­gine is restarted, the con­di­tions can al­low the code to be trig­gered.

The most likely causes of the prob­lem are ei­ther a poor con­nec­tion at the CTS ter­mi­nals or a breach within the wiring loom. As the coolant gauge ap­pears to read cor­rectly most of the time, and the cool­ing fans kick in at the cor­rect tem­per­a­ture, I would also check the air in­take sen­sor read­ing to en­sure that this isn't con­fus­ing the ECU. There is also a very slim chance that the ECU it­self is at fault, but this would be very rare.

In con­clu­sion, be­cause the prob­lem ap­peared to be rec­ti­fied for a short while af­ter the CTS was re­placed, this could have been be­cause the wiring loom was moved. This move­ment of the loom could have pos­si­bly al­tered the po­si­tion of the wires, in­ad­ver­tently fix­ing the prob­lem for a short time. Me­thod­i­cal check­ing of the wiring be­tween the sen­sor and the ECU would be my rec­om­men­da­tion.

The reader's Jaguar X-TYPE in­di­cates that it is over­heat­ing, but is ac­tu­ally run­ning nor­mally.

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