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DTC codes / Chrysler codes / P1765

P1765 · ChryslerTrans 12 Volt Supply Relay Control Circuit Open Or Shorted

P1765 on a Chrysler vehicle means the Transmission Control Module (TCM) has detected an open or shorted circuit in the control wire for the transmission 12-volt supply relay. The TCM expects to see a specific voltage on the relay control circuit when it commands the relay on or off, and the measured voltage falls outside that expected range.

SystemPowertrain
Code typeChrysler specific
SeverityMedium
Fix difficultyIntermediate
AreaTransmission

Symptoms you may notice

  • The malfunction indicator lamp (MIL) illuminates on the dashboard.
  • Often no symptoms besides the warning light, especially if the relay remains stuck closed and continues supplying power.
  • The transmission may enter limp mode, defaulting to a single gear or neutral, if the relay fails to supply power to the TCM or solenoids.
  • Harsh or erratic shifting, delayed engagement, or a complete loss of drive if the relay circuit is open.
  • The engine may crank but not start if the same relay supplies power to other critical circuits, depending on the vehicle's wiring.
  • Intermittent electrical glitches, such as flickering dashboard lights or random transmission codes, if the fault is a loose connection.

Common causes, most likely first

  1. A failed transmission 12-volt supply relay, often due to burnt contacts or a faulty coil.
  2. Corroded, loose, or damaged wiring or connectors in the relay control circuit, including the TCM-to-relay control wire.
  3. A short to ground or short to voltage on the relay control circuit, often caused by chafed wire insulation.
  4. An open circuit in the relay control wire, such as a broken wire or a poor terminal fit at the TCM or relay socket.
  5. A faulty TCM driver circuit that cannot properly command the relay, though this is less common.
  6. Blown fuses or poor power/ground connections to the relay or TCM that mimic a control circuit fault.

How to diagnose and fix it

  1. Verify the battery is fully charged and inspect the relay and TCM fuses; replace any blown fuse and retest.
  2. Locate the transmission 12-volt supply relay (often in the power distribution center) and swap it with an identical known-good relay to see if the code changes.
  3. Disconnect the relay and TCM connectors, then inspect terminals for corrosion, looseness, or damage; clean or repair as needed.
  4. Use a digital multimeter to check for continuity and shorts on the relay control wire between the TCM and the relay socket, referring to the factory wiring diagram.
  5. With the relay removed, use a test light or multimeter to verify the TCM provides a ground or voltage signal on the control circuit when the key is turned on.
  6. If the control circuit tests good, check the relay's power and ground circuits to ensure the relay can operate when commanded.
  7. Clear the code and perform a road test; if the code returns, diagnose the TCM or consult a dealer for advanced testing.

Relay control circuit checks that save time

  • A failed relay is the most common cause, but technicians often overlook a poor connection at the relay socket that only acts up when the vehicle is warm or vibrating.
  • The code can set intermittently due to a chafed wire that shorts only when the engine moves under load, so a wiggle test of the harness while monitoring live data is essential.
  • On some Chrysler vehicles, the transmission 12-volt supply relay also powers the TCM itself; if the relay fails open, the TCM may not communicate, leading to a no-start or no-scan condition that can be misdiagnosed as a dead TCM.
  • A shorted relay coil can blow the fuse that powers multiple circuits, so always check related fuses before condemning the TCM.
  • The TCM may set P1765 if the relay control circuit voltage is slightly out of range even though the relay still clicks, so do not assume the relay is good just because it operates.

Can I keep driving with P1765?

If the vehicle drives normally with only the warning light on, you can drive short distances to a repair shop, but avoid heavy loads or long trips because the transmission could enter limp mode without warning. If the transmission is already shifting harshly or has lost drive, stop driving and have the vehicle towed to prevent further damage.

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 Chrysler vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

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