ECU reset fault?
11 February 2012, 10:31 AM
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ECU reset fault?
Hi all last week I read the fault codes stored in the ecu, Only one code
21 coolant temp sensor having cleared the codes it came back so I changed
the sensor with a genuine part, Cleared the error code and it came back?
So yesterday I cleared it again and then checked the codes without starting
the car and with and the code it still there. I then tried dynamic code reading
I.E. green plugs connected whilst driving and 4 short pulses no code stored.
But if I plug just the black plugs in error code still shown? Any help or advice
please as I'm baffled
Colin.
21 coolant temp sensor having cleared the codes it came back so I changed
the sensor with a genuine part, Cleared the error code and it came back?
So yesterday I cleared it again and then checked the codes without starting
the car and with and the code it still there. I then tried dynamic code reading
I.E. green plugs connected whilst driving and 4 short pulses no code stored.
But if I plug just the black plugs in error code still shown? Any help or advice
please as I'm baffled
Colin.
12 February 2012, 11:13 AM
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OK I've not come across this one before but this would be my guess.
I suspect you have some sort of a wiring fault creating an intermittant error in the coolant temp sensor circuit. Could be the wires running back to the ECU, a connector betweent the sensor and the ECU or even something like a bad earth somewhere. The fault could even be inside the ECU on the PCB traces on the board (although this is well protected and less likely).
When the intermittant connection breaks, the ECU logs the code as a current fault but also logs it as a stored / historic code. The connection then makes again, the "current" fault code disappears but the code is retained in the stored / historic code list.
When you do an ECU reset, the ECU clears the historic/stored codes. As the stored codes get wiped and since the code is not "current" you just get the "all clear".
Note this is speculation on my part and may not be the right answer. It is a plausible theory however
Check over the wiring, any connectors the coolant temperature sensor goes through back to the ECU (e.g. engine loom connector, ecu connector) are clean and making a good connection. Check the engine earth is healthy (although this is less likely to be the cause because I would expect other problems to appear if it was). You could also try swapping the ECU for another one of the same type and see if the problem goes away (again, less likely to be the problem but an easy test if you can beg/steal/borrow an ecu for a few days).
I suspect you have some sort of a wiring fault creating an intermittant error in the coolant temp sensor circuit. Could be the wires running back to the ECU, a connector betweent the sensor and the ECU or even something like a bad earth somewhere. The fault could even be inside the ECU on the PCB traces on the board (although this is well protected and less likely).
When the intermittant connection breaks, the ECU logs the code as a current fault but also logs it as a stored / historic code. The connection then makes again, the "current" fault code disappears but the code is retained in the stored / historic code list.
When you do an ECU reset, the ECU clears the historic/stored codes. As the stored codes get wiped and since the code is not "current" you just get the "all clear".
Note this is speculation on my part and may not be the right answer. It is a plausible theory however
Check over the wiring, any connectors the coolant temperature sensor goes through back to the ECU (e.g. engine loom connector, ecu connector) are clean and making a good connection. Check the engine earth is healthy (although this is less likely to be the cause because I would expect other problems to appear if it was). You could also try swapping the ECU for another one of the same type and see if the problem goes away (again, less likely to be the problem but an easy test if you can beg/steal/borrow an ecu for a few days).
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