17978 – Engine Start Blocked by Immobilizer (VAG Golf IV, Bora, Passat B5, Audi A3 8L, A4 B5/B6, A6 C5, Octavia I, Fabia I, Leon 1M, Ibiza 6L)
On VAG vehicles, fault code 17978 (OBD2: P1570) means "Engine Start Blocked by Immobilizer". It is common on Golf IV, Bora, Passat B5, Audi A3 8L, A4 B5/B6, A6 C5, Octavia I, Fabia I, Leon 1M, Ibiza 6L, Petrol and TDI engines with immobilizer II/III (older KWP diagnostics) engines. Below are the real-world causes, step-by-step tests and OEM part numbers.
Last updated
17978 quick summary
| Fault code | 17978 |
|---|---|
| OBD2 code | P1570 |
| Meaning | Engine Start Blocked by Immobilizer |
| System | Powertrain (Engine & Transmission) |
| Vehicles | VAG (VW, Audi, Škoda, Seat) |
| Common on | Golf IV, Bora, Passat B5, Audi A3 8L, A4 B5/B6, A6 C5, Octavia I, Fabia I, Leon 1M, Ibiza 6L, Petrol and TDI engines with immobilizer II/III (older KWP diagnostics) |
| Severity | High |
| Can I drive? | The engine usually starts and dies after 1–2 seconds, so the car cannot be driven until the immobilizer accepts the key again. |
| Repair cost | €0 – €500 |
Symptoms of 17978
- Engine starts and stalls after 1–3 seconds
- Immobilizer / key light flashing in the instrument cluster
- Code also stored in the cluster or immobilizer module (often 01176 Key: Signal too Low)
- Problem appears after a battery change, cluster or ECU swap
- Sometimes only one key works
Most common causes of 17978 (most likely first)
Mechanic's Pro Tip
First confirm it really is the immobilizer: if the engine starts and cuts out after 2–3 seconds, it is; if it does not start at all, look elsewhere. Read the cluster (address 17) or immobilizer (25) for 01176 and check the measuring blocks – a key with a weak transponder or a cluster/ECU that is not matched causes most cases. Low battery voltage also upsets the immobilizer, so test with a good battery.
1.Key transponder not recognised or not matched (01176 Key: Signal too Low)
Most likely2.Instrument cluster or immobilizer module not matched after replacement
3.Engine control unit replaced or not matched to the immobilizer
4.Faulty reader coil around the ignition lock
5.Low battery voltage or faulty ECU power supply / relay
Step-by-step diagnostic guide
- 1
Read the engine (01) and the cluster/immobilizer (17 or 25) with VCDS or a VAG-capable scanner; note 01176 and other immobilizer codes.
- 2
Check the immobilizer measuring blocks: key status, 'Engine start allowed' and the number of matched keys.
- 3
Try the spare key – if it works, the main key's transponder is the problem.
- 4
Check battery voltage and the ECU power supply and relay with a known-good battery connected.
- 5
Match keys, cluster and/or ECU with the correct login/PIN or dealer online access; if nothing else is stored, a cold boot (both battery cables off and shorted together for about 15 s) sometimes helps.
Frequently asked questions
What is the difference between 17978 and P157000?
Both mean the immobilizer has blocked the engine. 17978/P1570 is shown by older VAG models with KWP diagnostics; newer UDS models show P157000. The causes and the fix are the same.
Can I fit a used instrument cluster or ECU?
Only if it is matched to your car's immobilizer. That needs the security PIN or online access and often all keys present.
Related fault codes
- P157000Engine Control Module (ECM) Disabled by Immobilizer
- 00532Supply Voltage B+ Signal Too Low
- 16684Random/Multiple Cylinder Misfire Detected (Older VAG 5-Digit Code)
- 17544Long Term Fuel Trim Add. Air, Bank 1: System Too Lean
- 17705Pressure Drop Between Turbocharger and Throttle Valve
- 17748Crankshaft/Camshaft Position Sensor Signals Out of Sequence
This guide is for information only. Working on vehicles can be dangerous — if you are unsure, have the car checked by a qualified mechanic. Values can differ between model years; always check the manufacturer's repair information.