2016 polo 1.4 tdi Non-start

[Chris1989]

Hi I have a 2016 polo 1.4 tdi (cusa), I bought the car as a non-runner told dues to a failed turbo after inspection the turbo had indeed failed and the shaft was broken, I replaced the turbo and checked and cleaned all associated parts but when trying to start the car it would turn over but not fire. The car will run if I spray brake cleaner into the intake unit I stop. I carried out a Diag scan and the only code present is p0562 (system voltage low). I replaced the battery but the code is permanent and won’t clear, I’ve checked all fuses and relays also replaced the Ecu with a cloned one but still can’t get the car to start. I’ve noticed that the lift pump in the tank isn’t priming or running on cranking but it can be operated via out put test. I’ve check to see if the injectors are being trigged and they don’t appear to be so I’m sure it’s a fuelling issue but im running out of ideas on what the cause of the problem is?

[ciclo]

Hi
Alternator?

[Chris1989]

I will check the alternator today I don’t know if that would cause a non start but definitely worth me checking

[ciclo]

As you already likely know, in addition to checking the battery terminals with a multimeter, make sure the power cable (G) and large fuses are in good condition.
hmm... also check the alternator cable connection to completely rule out that the fault comes from here.

[Chris1989]

Yes I’ve checked all main the fuses at the battery fuse box, I’ve checked the battery ground wire and the other engine bay grounds. I will check the power cable from the alternator today.
I did notice that when I get the car to run on brake cleaner I can then clear the p0562 code but it will then return after trying to start the engine normally and then won’t clear

[ciclo]

Is it manual or DSG?
I ask so we know if it's possible for you to do a "definitive" test.

The fact that code P0562 can be cleared when the engine is spun using brake cleaner () but returns immediately upon attempting a normal start confirms 100% that the problem is caused by a massive voltage drop at the exact moment the starter motor engages.

Do not look for fuel or ECU issues, the car is not injecting because the starter motor (or a faulty main cable) is causing a momentary voltage drop whenever you turn the key, triggering the ECU's lockout protocol.
The problem could be due to a shorted starter motor or a main positive or negative cable with extremely high resistance, or, the main relay might have burnt internal pins, causing the circuit to cut out under load, it depends largely on how insistently the previous owners tried to start the engine.

[Chris1989]

Hi the car is a manual transmission, thanks that does make sense what would you advise I check next?

[ciclo]

Try starting the car by pushing it, rolling it downhill, or towing it with another vehicle (not recommended if the driver does not have the necessary skills), with the ignition switch set to "ON".
If the car starts immediately upon releasing the clutch, the starter motor is faulty and needs to be replaced.

A quick reminder: Ensure the power and ground cables are securely connected and in good condition, we want to avoid any cable that was handled during repairs coming loose or not being properly secured.

[Chris1989]

Ok thanks il double check all the leads and try to tow start it tonight and let you know how I get on

[Chris1989]

So I’ve been really busy the past week but I got around to trying to tow start the car and after towing the car a mile or so it finally started although only on two cylinders but at least it started, I then cleared the fault codes after letting it idle for 5 mins and the car now restarts on the key.
I now just have to find out the cause of the misfire,
There were no misfire codes but if I unplugged the injector plugs one at a time while the car idled cylinder 3 made no difference but it did put a open circuit code for that injector because I unplugged it.
I e done a compression test on all 3 cylinders and number 3 is slightly lower but still just within spec.
I think maybe I should try swapping 1&3 injectors to see if the misfire moves?

[ciclo]

Great news! You successfully isolated the starter motor draw, and getting the ECU clean voltage by tow-starting it was the definitive fix for the P0562 code.

Now, regarding the cylinder 3 misfire, swapping injectors 1 and 3 is exactly the right next step to isolate the issue. However, since this car suffered a catastrophic turbo failure, you need to be very careful.

Here is a step-by-step on how to proceed to find the real culprit.

Step 1: Visual Inspection and Injector Swap.
Inspect the tip: When you pull out injector 3, look closely at the nozzle under a good light. Check if it is physically damaged, bent, or clogged with burnt oil/debris from the turbo failure.
Seals: Always use new copper crush washers and O-rings when installing them back... reusing old washers will cause compression leaks and ruin your test.
The Test: Swap injector 1 and 3. Don't worry about recoding them in the ECU (IMA codes) just for a quick test; it will run well enough to see if the misfire moves.
The Result:
-If the misfire moves to cylinder 1, the injector is dead.
-If the misfire stays on cylinder 3, the problem is mechanical/internal to the engine.


Step 2: Check for Fuel Contamination (High-Pressure Pump).
Before spending money on a new injector, open your fuel filter housing. Check with a flashlight if there are any tiny metallic shavings (shimmering glitter) at the bottom.
If the previous owner cranked the car dry repeatedly, the high-pressure pump might have generated metal flakes. Cylinder 3 is at the end of the fuel rail, so it usually gets blocked first.


Step 3: Analyze the "Borderline" Compression.
You mentioned cylinder 3 compression is slightly lower but "within spec". When a turbo shaft snaps, a massive amount of engine oil gets pushed straight into the intake. If oil entered cylinder 3 while the engine was running, it can cause a mild hydro-lock, which slightly bends the connecting rod. A slightly bent rod lowers the compression just enough so the air doesn't get hot enough at idle to ignite the diesel properly, causing a constant misfire without triggering an electrical fault code.

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To help you narrow this down, could you let us know:
- What were the exact compression numbers (psi or bar) for all 3 cylinders?
- Did you thoroughly clean the intercooler and all intake piping of oil before installing the new turbo?


Good luck, you are very close to fixing this car!