Not starting.

Hi

Sometimes you said 'Coolant fan' which is as you say, a petrol problem.

But you also have other faults mixed in the post and say 'fan blasting' which could be the heater blower fan, which is a common problem to be on full and not related to the fuel type.

jamesrabel wrote: ↑Fri Jul 22, 2022 11:50 am First pro with obd2 reader says its thermostat. Not thermostat.
Second pro with obd2 says its air throttle housing, not air throttle housing.

The problem with this is that the codes read give just 'error codes'. This does not necessarily mean the sensor has failed, even if a sensor is mentioned in the fault. What the codes say is 'this sensor has detected a value that is unexpected'. Often it can be the output stuck at 0v (shorted to ground) or stuck at +12v or 5v (shorted to supply) or a variable output not in the expected range for a particular situation of the engine state.

While changing sensors can clear a fault, it doesn't always happen like that. You can have a good sensor, poor wiring or good sensor, and unexpected situation.

The actual error code and its description that lexia/diagbox gives is one of the most useful pieces of screengrab information you can get.

You can test a thermostat on the bench if you wanted to prove it was working properly in place of changing it.

The air throttle fault, (whatever code it was?) could be showing that a received signal is beyond one that is expected at a particular engine load. This does not point to a faulty air throttle valve unless it is not actually working properly. Difficult to test, but with a substitution and the fault still present, re-read the codes.

The codes being the same or different can help and knowing what each code read shows gives invaluable information on what the ECU is reading.

If you have a non starter but turns over, go back to your basics and check each of them.

Immo, you need a immobiliser pass from the Key to start the engine
Fuel, you need fuel at the output of the injectors
The spark is required and at the right time - coil pack and plugs
The cam and crank need to be in synchronisation - provided by the cam belt
The ECU needs to know when each revolution has completed, that would be due to a crank or cam position sensor or a combination of them.

If you don't have the basics, it will never start, well, 'easy start' may get it running for all but the came belt one

jamesrabel wrote: ↑Fri Jul 22, 2022 11:50 am engine light on, and very poor cold performance

This engine light is the car telling you not to drive it, but rather read the codes to see what the ECU is trying to tell you.

You see thats the problem, i have been over the basics. The "pros" i went to see before swapped out thermostat or air throttle, cleared errors, then the car was fine. Car ran for a week or two, then broke down. That happened three times. Now there is no errors on the ecu from the last reading. I cant get another reader for the time being but im gonna assume that the car has not accumulated extra errors while still not moving and not much being done to it.

I have fuel, air. Spark, cant check with the gear I have. Look, I know you should always run over the classics, but this problem just keeps shouting radiator fan at me. I mentionned the car did work very rarely. Only times the fan was working as intended. I checked all the cables that I know of leading from engine sensor to ECU, checking an faulty earth (unrelated). I even checked the diagram and checked every goddamn cable communicating with the ecu, all the way to the fan, they all read non faulty on a voltmeter. Something is forcing the relay in "on" position, when unplugged it stays in off. That means ECU is telling the cooling fan to go 100% to cool the engine

I know for A FACT that if the ECU is telling the radiator coolant fan to go full blast, it wont let the c3 start, i have seen it in about 4 different topics. But it was always the sensor. Im stumped because its not the sensor in my case and im running out of ideas.

jamesrabel wrote: ↑Fri Jul 22, 2022 4:16 pm Something is forcing the relay in "on" position, when unplugged it stays in off. That means ECU is telling the cooling fan to go 100% to cool the engine

Or could it mean the relay is faulty and it is not the ECU telling the relay to go on. Its just the relay stuck 'on'?

I don't know if you disconnected the power or the control lines from the relay?

The relay itself, when unpowered and removed stays in position 4 on the diagram, which means off. As soon as ignition is primed with key, it hops to 5. All i know is that the circuit is powered the moment the car is powered.
I read the diagram, the current has to pass through the ECU to decide what to do with the cooler fan.
Im starting to think i actually have a defective ECU

jamesrabel wrote: ↑Wed Jul 13, 2022 8:03 pm with the air throttle flapping everywhere. This is despite the fact i put the original air throttle back on

jamesrabel wrote: ↑Fri Jul 22, 2022 11:16 pm Im starting to think i actually have a defective ECU

If you are saying that the "butterfly valve" in the throttle body is "flapping backwards and forwards" then that's not good. It shouldn't move backwards and forwards (on it's own) even if there is a problem with the throttle body. The engine ECU should detect this and shut down. The only explanation is that the engine ECU is actually driving it when it shouldn't be!
Yes, I would say the engine ECU is bad. That does explain a lot of your unusual symptoms, including not being able to read it on the OBDII scanner.
Although, your problem is intermittent. Can't really explain that one, except shi...stuff happens!
Have you checked the electrical connectors at the engine ECU for corrosion? Possibly bad power to the ECU?
The engine ECU's are typically very reliable and would normally be one of the last things I would suspect. But then again, stuff happens!

True as you say, stuff happens...

Theres definetly no corrosion, but i read somewhere on here that petrol 2003 may not be an easy read for generic obd2, my last hope would be my friends reading tool. It was worth 700 euros back in the day, should be able to hook to my car but i gotta wait a week to get it.

The air throttle flapping is not even flapping anymore, just the fan now. I dont understand any of these faults.

I ws looking at wirings diagrams, the relay i have is for petrol models without air con, yet I have air con, but for the life of me i cant find the fuse for it.

Is there a chance that the relay is actually the wrong one? I dont know if its the original...
I know the AC system makes the fan come on even on cold, could that actually stop a car?

jamesrabel wrote: ↑Sat Jul 23, 2022 8:34 am
I know the AC system makes the fan come on even on cold, could that actually stop a car?

No. A fault in the radiator fan or control circuit will not stop the engine from running.

You have NOT proven that the ignition or injection systems are working!

To PROVE they are working;
The coil pack and spark plugs would need to be removed from the engine and the spark plugs observed...sparking.
The injector rail and injectors would need to be removed from the engine and the injectors observed squirting fuel.
I don't recall you saying you did that.


For an engine to work you need;
Oxygen. Tick, got plenty of that.
Compression. The chances of all 4 cylinders having so low a compression as to not allow the engine to, at least cough and splutter, is astronomical! Tick, compression most likely OK.
Spark. Hmm unknown. X
Fuel. Hmm unknown. X

You can try squirting "aero start", brake clean or the like down the "air throttle". If it pops and far...runs badly, you have a fuel problem. If nothing happens then you have an ignition problem or ignition and fuel problem.

Try "starting fluid" down the throttle body next. (follow the directions on the can!)

Im actually waiting for my friends obd2, its a lot better than the one i have. Before i check coil pack/injectors, i wanna run a full diag on it, see if can actually point me in that direction. Thanks for the ideas though, if the diag reads no errors im gonna go down that path.
I didnt know about the brake cleaner trick thanks for that. I will keep the thread updated in the next week!