Thread: 300 tdi intermittently wont start

Originally Posted by loanrangie

Run a wire from battery to solenoid and see if it starts, when mine did this it was the alarm module.

Replaced relay - no change
Replaced key fob battery - no change
Fuses all ok

Ran power to solenoid - starts

Looks like back to mech to sort out..at least I can drive it.

Originally Posted by edddo

Replaced relay - no change
Replaced key fob battery - no change
Fuses all ok

Ran power to solenoid - starts

Looks like back to mech to sort out..at least I can drive it.

Have you checked the auto trans inhibitor switch?

Originally Posted by Old Farang

Have you checked the auto trans inhibitor switch?

No..is it easy enough to get to to inspect?

Originally Posted by edddo

No..is it easy enough to get to to inspect?

Sorry mate, not sure just where it is on your car. There is also a relay involved, and a diode on some. Really need the circuit diagram for your car so that you can test the circuit without having to wreck half the car to get at it.

Originally Posted by edddo

No..is it easy enough to get to to inspect?

Assuming the tdi is the auto in your sig:

Firstly have you tried to start it in neutral?, or only in park?
Trans inhibitor switch is on the passengers side of the trans body, above the selector rod lever.

But! when you say you ran power to the starter solenoid, did you run a cable to the solenoid and then start it via the key?
OR, did you jumper start it with the power cable, that is direct start with the external power cable?
Makes a difference.
Reason for asking is, have you checked that the starter component of ignition switch actually works?

(now I may be wrong in this next section)!!
My understanding of the electrics is that if the trans interlock isn't working, it cuts power to fuse F12 in the interior fuse panel.
So if you have ignition on, and power out of fuse F12 under the drivers panel, then the trans interlock is working .. no need to test it at the trans.
If no power (with ign on) on F12, then at the trans end.

Most common cause for this type of non start(assuming you're just not getting any cranking at all) is that the wiring to the starter solenoid is old and most likely flaky.
Second most common issue will be the solenoid.

Before you go to the trouble to change your solenoid, I'd test everything at the start section:
back inside, I guess you tested Fuse F17 and F12?
Also, at the ign switch, test voltage(or test light .. but voltage better) on the white/red wire when you hit the starter with the key.
This is the wire that sends power to the relay, and onwards from there. If you have power on this white/red wire, then ign switch OK.
You said you already changed(or tested) the relay .. so from there, I'd check the white red wire plug condition at the starter solenoid end.

Also the good old 'tappy tap tap' on the solenoid .. if that does it .. obviously change it!

Originally Posted by AK83

Assuming the tdi is the auto in your sig:

Firstly have you tried to start it in neutral?, or only in park?
Trans inhibitor switch is on the passengers side of the trans body, above the selector rod lever.

But! when you say you ran power to the starter solenoid, did you run a cable to the solenoid and then start it via the key?
OR, did you jumper start it with the power cable, that is direct start with the external power cable?
Makes a difference.
Reason for asking is, have you checked that the starter component of ignition switch actually works?

(now I may be wrong in this next section)!!
My understanding of the electrics is that if the trans interlock isn't working, it cuts power to fuse F12 in the interior fuse panel.
So if you have ignition on, and power out of fuse F12 under the drivers panel, then the trans interlock is working .. no need to test it at the trans.
If no power (with ign on) on F12, then at the trans end.

Most common cause for this type of non start(assuming you're just not getting any cranking at all) is that the wiring to the starter solenoid is old and most likely flaky.
Second most common issue will be the solenoid.

Before you go to the trouble to change your solenoid, I'd test everything at the start section:
back inside, I guess you tested Fuse F17 and F12?
Also, at the ign switch, test voltage(or test light .. but voltage better) on the white/red wire when you hit the starter with the key.
This is the wire that sends power to the relay, and onwards from there. If you have power on this white/red wire, then ign switch OK.
You said you already changed(or tested) the relay .. so from there, I'd check the white red wire plug condition at the starter solenoid end.

Also the good old 'tappy tap tap' on the solenoid .. if that does it .. obviously change it!

Hi AK
was hoping you would chime in.
Yes i inspected those fuses and replaced the starter relay.
I started the car by running power to the solenoid while ingnition was on.
I now have a wire connected to the solenoid and to start I turn key on and touch the wire to the battery.
I will check the ignition wire but everything else...radio, low coolant alarm..powers up normally with the key.

update (and edit)

12.1 volts at fuse 12 with key in on ( not start) position
however - that voltage would not light the test bulb? - what does that mean?

11.1 volts at ignition wire ( red/white) going into starter relay ( using black/brown terminal on plug for earth) - when key is is turned to start position ie full clockwise. That is too low yes? The battery is a bit low at 12.1(12.4 after short run) but it cranked ok and started immediately just now.

See attached pic - there is a white wire that is spliced into the earth(black/brown) wire on the relay. It has a washer connector as if it is/was meant to be attached to another earth point. But I cant see any sign of any such point - or any evidence that it has ever been attached to anything becuase the sheath on the wire was fully covering the end anyway. I suspect this is a furphy - Arthur does this make any sense?
I did attach it to a local earth point but it made no difference ie still now power to starter.

edit:
since I wrote the above:
I took steering shroud off to get at ignition wire at source. With a good earth to body the voltage at ignition wire with key in start position was 12.3V...more or less same as battery.
Then using the same earth I checked again at the starter relay and also got 12.3V.

The only thing that looks wrong is the 11.1V at the relay when I use the internal earth - it needs 12 to activate the circuit doesnt it? But I am confused about this because with an independent earth it reads 12.3V which means that the relay is getting power.

So is it reasonable to conclude:

Ignition circuit and key barrel are ok
Inhibitor switch is ok
Problem is between relay and solenoid
So it is either a basic short/break or the alarm module ( which I thought was bypassed)

?



thks

relay2.jpg

Just quicklyI have to get to work)

That white wire with the loop end looks like it's an added earth, most likely due to some issue by a previous owner.
Maybe reconnect it to a good metal point and see if that helps the relay get a better earth than the 11.1 you measured.

So at the moment, the likely suspects appear to be as you listed. And possibly this mysterious diode that was mentioned previously by Old Farang.

Starter relay diode is marked as Z158 in RAVE's electrical library(do you have RAVE?). location is near the starter relay, looks to be a bit higher up and forward.
Should have a Black and Orange wire(coming off the starter relay), and a Black and Yellow from it that goes to the trans inhibitor/cruise control/alarm units.

ps. not too sure if all D1's have this diode tho, but would pay to check for it.

If I have the time after work, I'll check mine to see if I have one of these diodes too.
Unlikely for me tho as I have no factory cruise(mine's after market), nor alarm .. would be nice to know if I have one and it's something to do with the auto trans inhibitor.