Hot Start Problem on VAG 1.9/2.0 TDI PD: EDC16U1 and EDC16U34 Fixes for Golf, Caddy, Touran

A 2006 Caddy 1.9 TDI BLS starts first turn in the morning, drives to the supermarket, sits for twenty minutes, and then cranks for ten seconds before it catches with a cloud of white smoke. On a bad day it doesn’t catch at all until it’s cooled down. The owner has already had a battery, glow plugs and a fuel filter. This is the PD hot start problem, and it has more than one cause, so the order of checks matters.

What’s happening at a hot start

At cranking the ECU needs a crank signal (G28), a cam signal (G40) to find the injection order, PD injectors that build pressure mechanically from the cam, fuel in the tandem pump without air, and a start quantity from the calibration that matches fuel and coolant temperature. Hot, the fuel is thin, the injector solenoids are at their slowest and any leak lets pressure bleed off. The ECU also reduces the start quantity at high fuel temperature to avoid smoke. Combine a tired injector with a conservative start map and you get exactly the long crank.

Check in this order

1. Live data during the failed hot start, with VCDS groups 001 and 004 on the engine module: rpm while cranking, coolant temperature, fuel temperature, start quantity. If rpm shows zero while the engine is spinning, the G28 crank sensor is dropping out hot. Very common on 1.9 PD; replace it and stop there.
2. Fuel temperature (G81, in the fuel return on the head). A sensor reading 80 °C or more when the engine has been sitting cuts start quantity hard. Compare with coolant; more than 15 to 20 degrees difference means a bad sensor.
3. Air in the fuel. Clear hose on the return line, look for bubbles at idle. Tandem pump seals, a cracked fuel filter housing, the seals on the injector loops in the head, and the T-piece in the return all let air in. Diesel in the oil (oil level rising, diesel smell) points at the tandem pump.
4. Injector harness inside the rocker cover. The insulation goes brittle and shorts to the cover when hot. VCDS shows intermittent injector circuit codes P0201 to P0204, or nothing at all. Wiggle test with the cover off.
5. Cylinder balance in group 013 at hot idle. One cylinder at the limit means an injector or a worn cam lobe (PD cams on BKD, BXE and AXR wear the lobes under the injector rockers).
6. Compression, hot. PD engines with 300,000 km lose enough that the hot start quantity is no longer sufficient.

What about the immobilizer?

A slow immobilizer handshake (worn transponder, dirty reader coil, or a cluster with a tired EEPROM) delays the injector release by a second or two, hot or cold. It feels like a hot start issue when the car is used for short trips. VCDS shows the immobilizer status in the cluster module; if it’s not the immobilizer, don’t go down the immo off route for this.

The ‘hot start OK’ file

When the mechanical checks come back clean-ish, or the owner won’t pay for injectors and a cam on a 250,000 km car, the calibration can compensate. The fix on EDC16U1 and EDC16U34 changes the start injection quantity maps against coolant and fuel temperature, the start rpm thresholds where the ECU hands over from start to run quantity, and the fuel temperature correction so a hot soak doesn’t strangle the start. Done properly the engine catches within one to two seconds hot, with a small puff of smoke. It’s a compensation, not a repair; it doesn’t fix a leaking pump or a dying crank sensor, and if those are the cause the file changes nothing.

Reference reads for these units: VW CADDY EDC16U1 0281011882 03G906016DM 6045 1037371251 HOT START OK is the finished solution for that Caddy, and the originals AUDI A3 EDC16U1 0281011847 03G906016BA 7000 1037371953, VW GOLF EDC16U34 0281013228 03G906021KK 9183 1037381019 and VW TOURAN EDC16U34 0281013617 03G906021HN 9968 1037394984 cover the common 1.9 and 2.0 PD software. Earlier EDC15P cars (VW PASSAT EDC15P+ 0281010543 038906019DS 1348 1037360705, SEAT IBIZA EDC15P+ 0281011244 045906019BG 5180 1037368177) have the same maps in a simpler layout. All read by OBD with KESS V2, MPPS or Galletto; EDC16U34 needs the right protocol selected or it hangs on recovery.

If you want the fix, send us the full read, the engine code, the VCDS live data from a failed start if you have it, and what’s been replaced. That goes through the request form. Model pages: EDC16U1, EDC16U34, EDC15P.