Hi,

Just returned from holiday to cold snap and my Nov. 2000 Octavia 1.9TDi is difficult to start from cold, engine code ALH.

Heater plugs measure 1.7 ohms each in situ, all fuses under dash intact.

If I disconnect water temp. sender to simulate cold start and measure voltage to heater plugs on start up there is no voltage.

Suspect ECU, heater plug relay or heater plug fuse.

Does anyone know where the heater plug relay and fuse is situated my Haynes manual do not mention them.

Thanks

PS originally posted in new members forum by mistake

Hi Martin,

Did you get to the bottom of your problem as I have a similar story. No voltage at heater plugs on cold start. I can hear a clicking from the engine compartment but cant find the relay.

Any advice would be greatly appreciated.

Jb

Will it start with the temperature sensor disconnected?, are the glow plugs OK?

We had one a while back, two of the glow plugs had gone down, we put a set in and it still had starting problems.

We found that it would start normally with the temperature sensor disconnected. We took it to an auto electrician who diagnosed an ECU fault. The customer did not want to pay for a new ECU, so he wired up a manually operated switch to disconnect the ECU side of the temperature sender when starting.

Same problem so want to use the same solution, however there are four cables in the temp sensor plug. So which one should I cut and then switch operate?

I can't really remember, I vaguely recall that it might have been a purple one. Basically it is a 4 pin sender, one pair of wires for the gauge and the other pair for the ECU. You should be able to work it out from the relevant wiring diagram for your engine code and year of car.

I'm interested to hear what the outcome of this is as well, as mine is having a few problems starting in the cold (have to hold the key for a second or two as it struggles to life, and a bit of smoke) and it's a bit embarassing! Once it's started the first time it'll start immediately and with no problems the second time, even if you switch the engine back off immediately.

EDIT: Just found this thread which might resolve the smoke problem at least!

http://briskoda.net/ask-tech/octy-1-tdi-question-smokey-starting/131351/

Edited 30 December, 200817 yr by metalangel

Help please, from anyone with a wiring diagram - which I haven't!

None, they provide info for your fueling and dash temp readout - if faulty spend

Note - anyone with cold starting issues should have the static timing checked, as the tdi starts well down to freezing with no glow plugs, providing the timing is set to the advanced (upper) limit in vcds.

Greg.

Disconnecting the sensor and the glow plugs work (all just renewed) so can it be the relay?

The fault occured at the start of the coldest period a few weeks ago, no starting, running, or fuel consumption issues otherwise so I fail to see how the timing can be a problem?

So the colour of the wire that runs to the ECU, please?

The glow plug relay is situated under the dash in front of brake pedal with the other relays. The glow plug relay has four terminals in total, two large spade terminals and two smaller ones.

On one of the two large terminals will be a permanent battery live 12V supply. Check to make sure that there is. The other large terminal will go to the glow plugs. Check for continuity between this terminal and earth. You will be measuring the total resistance of the glow plug circuit. NB. This test will not prove that all the glow plugs are working.

One of the two smaller terminals is an 'Ignition Live'. You will measure 12V here with the ignition on. The other smaller terminal is an ECU switched earth. The best way to test is to use an LED test lamp. Connect one end to a live supply and then probe the Relay terminal. When the lamp is on the ECU is earthing the relay, and so it will be switched on, thus switching on the glow plugs.

It's important that you do not use a conventional test lamp for this as the bulb's resistance is quite low. It will therefore draw current and it's possible that the ECU could be damaged. LED test lamps are completely safe because any current they draw at all is barely measurable. You could also use a voltmeter to check the ECU switched earth, but remember a voltmeter measures potential difference between two points of a circuit. It does not measure presence of current. This is where many people become confused and simply don't understand what the voltmeter is telling them. The meter does not know how to lie. If it shows a reading then that's what it is. People interpret that reading incorrectly, and that's why voltmeters end up back on the shelf never to be used again. A voltmeter is an excellent diagnostic tool, if it's used correctly.

Edited 31 December, 200817 yr by Railroad

In my day it was a blast of EasyStart down the air cleaner, never failed.

In my day it was a blast of EasyStart down the air cleaner, never failed.

That's definitely not recommended for diesel engines as serious damage can occur. The highly volatile product causes premature combustion, and will try to force the piston down the cylinder while the crankshaft is trying to push it up. Something therefore has to give, and it's usually the con-rods which become bent. The compression ratio is then lowered and starting is even more difficult. That's why people say engines become addicted to Easy Start, 'cos in effect they do.......

Yep thanks railroad, have testers and used them many times. The relay is working and switches the plugs correctly - ONLY if the sensor is disconnected, plug it back in and nothing. So all I want is the colour of the cable that runs to the ECU as the sensor is operating the temp gauge correctly and tests fine on VAG COM, it seems to be the ECU that is not correctly earthing the relay . I could buy a Haynes manual but was hoping someone may know.

You do NOT want to bodge this. The 'sensor' is actually two sensors, one to the dash and one to the engine. If the one to the engine is faulty, there lies your issue. It doesn't have to give a fault code to be worth the

Hi, how the.... do you unplug the dam thing, the connector just wont budge. Want to disconnect to try see if it cold starts better as its a bit hard and smokey spluttery when cold. ok rest of time when hot. It was hard to get the connectoer off the sensor on pipe just from the air box. had to get screw driver to prise it off. [pasted to a few thread ends]