Hi All,

I would like an opinion on this please. This vehicle over-heated and soon after ran badly with EML illuninated. Customers scanner showed Fault Code PO 115 - Coolant Temperature Circuit. The sensor was replaced but ran just as badly when yours truly was invited to have a look.

I found the same Fault Code plus U1601 which I now believe to be CANBUS fault. On scanning, I found that the MAP Sensor was reading very high and the Air Temp Sensor very low at about -30c. The CTS was reading about -6c with a voltage of approx 4.8v. The earth wire was reading 4.2v. Now on this vehicle (where the ECU is bolted to the throttle body), the ATS is incorporated in with the MAP sensor and the poor readings were due to a non existant earth. The earth wire was carrying 4.7v.

Now, I decided to piggy back an earth to the coolant temp sensor and immediately found that the common earth returned to the MAP/ATS and the vehicle began to run reasonably well. Thinking I had cracked it, I noticed that the EML was still illuminating with Fault code PO115. The voltage to the CTS remains at 4.9v and reads 6c. From my wiring diagram I note that the 2 wires to the CTS run direct to the ECU.

So as far as I can see, the second CTS could be faulty, or the ECU could be faulty or the earth wire is picking up a stray 5v in the loom some-where. Where did the 2 earths go in the first place? The common point is the ECU. Could the ECU be damaged by the overheating engine?

I welcome your expert opinions.

Regards

Pete M