Hi!
I have a 2004 Punto with the 1.2 liter 8V engine. Recently I did some maintenance work (timing belt, spark plugs etc.). The car was working fine before that (except for occasional power steering isues). Now after the maintenace work the car runs only for few minutes until the engine suddenly dies. When that happens, there seems to be no connection to the ECU. The engine doesn't start (cranks fine, but probably no spark and/or fuel) and I cannot connect to the ECU through the OBD2 port. If I wait for a while, or if I disconnect and reconnect the battery, the ECU connection seems to work again and the engine starts fine and runs again for few minutes max. This happens over and over again. It seems like the ECU just shuts down suddenly or is unable to communicate when the issue triggers. All the accessories like blower motor, lights, radio etc. continue to operate normally.
I have tried to:
I have a 2004 Punto with the 1.2 liter 8V engine. Recently I did some maintenance work (timing belt, spark plugs etc.). The car was working fine before that (except for occasional power steering isues). Now after the maintenace work the car runs only for few minutes until the engine suddenly dies. When that happens, there seems to be no connection to the ECU. The engine doesn't start (cranks fine, but probably no spark and/or fuel) and I cannot connect to the ECU through the OBD2 port. If I wait for a while, or if I disconnect and reconnect the battery, the ECU connection seems to work again and the engine starts fine and runs again for few minutes max. This happens over and over again. It seems like the ECU just shuts down suddenly or is unable to communicate when the issue triggers. All the accessories like blower motor, lights, radio etc. continue to operate normally.
I have tried to:
- Read the fault codes (with a generic reader). Usually there isn't any codes at all. Maybe once per ten attempts it might throw some codes, but hard to say if they are related. One time I got codes U1600, U1602, P1325 and one time I got some coil-related codes. Dash seem to also lose connection to the ECU, because it might blink the odometer, blink the ABS and brake indicators or burn the yellow immobilizer light. When the engine starts and a connection to the ECU exists, there are no error indications on the dash.
- Monitor live data using a generic scanner. The connection to the ECU drops immediately when the engine dies, so nothing abnormal can be seen there. At least in the basic values that I could see.
- Disconnect and reconnect most of the wire harness connectors and clean the battery cables and terminals.
- Clean and measure the ground cable to the throttle body / ECU.
- Measure the voltage when the engine is running. Alternator is working and the voltage seems normal.
- Add extra ground wires to the engine and throttle body / ECU.
- Poke the cables and connectors when the engine is running to see if it has any effect -> nothing.
- Swap some random relays with identical ones from different places. Most likely I swapped all of those ECU relays too, but I'm not sure anymore.
- Remove the battery. It was actually removed for couple weeks because of the maintenance work.
- Warm or coold down the engine. Exact engine temperature does't seem to have any noticeable effect, so most likely not a thermal expansion issue.
- Wire harness. I had to disconnect most of the connectors and I moved the harness a bit during the maintenance work. I don't see any clear damage, but maybe there could be a short circuit somewhere and the ECU goes to some kind of safety mode for a while because of that? Or maybe there is a voltage drop which causes a brownout for the ECU?
- Broken ECU. It would be bad luck if the ECU happened to break when it was almost untouched when the car sat in the garage. However, this would explain the sudden deaths of the engine and also the lack of connection to the ECU when the issue is active.
- Broken ignition components. I have read that the coils are a common fault in these engines and they might kill the ECU. Not sure if a broken coil, a spark plug or a spark plug cable could "tease" the ECU so badly that it shuts down after a while. I changed the spark plugs during the maintenance, but they should be similar to the old ones.
- Immobilizer. I would assume that the engine would not start, or at least not run for so long time, if this was the case. Also I don't think it should prevent any connection to the ECU even if the immobilizer triggers. Also the yellow immobilizer light only comes (not every time) if I try to start the engine again immediately when the issue occurs, but that might be because of the missing ECU connection.
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