Fiat Punto 1.2 2001 - Poor running, code P0115 & U1601 MIL on #
Posted by Pete Mutlow on June 29, 2012, 4:43 pm
Year of Manufacture *: 2001 Engine Size and Code *: 1200cc ( Optional ) ECU Type: Marelli IAW 59F ( Optional ) Scanner Used: ACR4 G2 ( Optional) Fault Codes: PO 115 , U1601
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
Re: Fiat Punto - poor running
Posted by Mark Carter on June 29, 2012, 7:00 pm, in reply to "Fiat Punto - poor running" Mark Carter
Hi Pete,
Two questions to think about;
The first question is why is the "Earth" for the sensors coming from the ECU, why not a proper chassis Earth?
The second may be where does the ECU get the Earth from to "give out" to the sensor circuit.
Regards MarkModern cars, Its all wizardry and witchcraft
Thanks for that. Guess I am going to learn something here plus other techs looking in which is always a good thing.
I have made the assumption that the ECU earths the various sensors as a normal progression of electronics bearing in mind how the old earthing points used to corrode etc.
I have also made the assumption that the ECU has an earth somewhere to provide the earth path for the other sensors. But if this is broken, then the vehicle will not run.
Spot on, Fiachra, I had one last week, non start, the 8 mm bolt on the top front of throttle body was loose. Tightened bolt and engine started.Sounds simple, but was only found after 2 hours of testing lives and earths!Fault codes were for ignition failure, coils A and B.The ECU had been sent for testing and no fault found. Regards, Gwyn
on June 29, 2012, 7:00 pm, in reply to "