01 Fuel Pressure Regulator Issues: Symptoms and Repairs • 02 The Future of Mechanics: Skills That Will Make You Rich • 03 How do driverless cars navigate without road markings? • 04 P0065, P0066, and P0067: Air Assisted Injector Control • 05 Optimizing Engine Performance: The Critical Need for Oil Fi… • 06 Introducing D-CAT: Diesel Clean Advanced Technology for Imp… • 07 General Motors: A History of Innovation and Leadership • 08 100 Hilarious Things Mechanics Actually Say (That’ll Make Y… • 09 Unlocking the Power of Differential Lock: Traction, Problem… • 10 This Rolls-Royce Has An Umbrella That Dries Itself Inside T… •

DTC codes / Volkswagen codes / P1747

P1747 · VolkswagenTransmission Control Unit Relay Open Short To Ground

P1747 on Volkswagen vehicles indicates that the Transmission Control Module (TCM) has detected an open circuit or a short to ground in the relay that supplies power to the transmission control unit. The TCM monitors the relay's control circuit and expects a specific voltage; when the voltage is outside the expected range, it sets this code and may disable the relay, cutting power to the transmission electronics.

SystemPowertrain
Code typeVolkswagen specific
SeverityMedium
Fix difficultyIntermediate
AreaTransmission

Symptoms you may notice

  • The transmission may enter limp mode, staying in a single gear or refusing to shift.
  • The gear indicator on the instrument cluster may flash or show an error.
  • The engine may crank but not start if the relay also supplies power to other components.
  • Intermittent loss of power to the transmission control unit, causing erratic shifting.
  • Often no symptoms besides the warning light, especially if the fault is intermittent.

Common causes, most likely first

  1. Failed transmission control unit relay (often located in the relay panel under the dashboard or in the engine bay fuse box).
  2. Corroded or loose electrical connectors at the relay or TCM.
  3. Damaged wiring harness between the relay and the TCM, often due to chafing or heat exposure.
  4. Blown fuse that supplies power to the relay circuit.
  5. Internal fault in the TCM causing it to misread the relay circuit.
  6. Water intrusion into the relay panel or TCM connector, leading to corrosion.

How to diagnose and fix it

  1. Check all fuses related to the transmission control system and replace any blown ones.
  2. Inspect the transmission control unit relay; swap it with an identical known-good relay to see if the code clears.
  3. Disconnect the TCM connector and inspect for corrosion, bent pins, or water intrusion; clean and dry as needed.
  4. Perform a voltage drop test on the relay control circuit and power supply wires to the TCM.
  5. Check the wiring harness for continuity and shorts to ground between the relay and TCM, repairing any damaged sections.
  6. Clear the code and test-drive the vehicle to verify the repair; if the code returns, recheck the TCM and relay socket.
  7. If all external circuits test good, suspect the TCM itself and follow Volkswagen diagnostic procedures for module testing.

Relay circuit faults often misdiagnosed

  • A faulty relay can cause the TCM to lose power intermittently, but the relay may test fine with a simple click test; always check for voltage drop under load.
  • Corrosion at the relay panel is common on older Volkswagens due to water leaks from the windshield cowl or sunroof drains, which can mimic a failed relay.
  • The code description mentions 'open short to ground,' which can be confusing; it means the circuit is either open or shorted to ground, not both simultaneously.
  • A weak battery or poor ground connection can cause the TCM to set this code falsely, so always verify battery health and ground straps first.
  • Some aftermarket alarm or remote start installations tap into the relay circuit and can introduce faults that trigger P1747.

Can I keep driving with P1747?

If the transmission is in limp mode or shifting erratically, avoid driving at high speeds or under heavy load and seek repair promptly. If the only symptom is the warning light and the car drives normally, you can drive cautiously to a workshop, but do not ignore the code as it may worsen.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

Guidance is general and written for Volkswagen vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

Running on fumes Free guides aren't free to make. Top up the tank. Any amount, one time. Fuel the Garage