🚨 Diagnostic Profile
Vehicle Make: Dodge
Description: Transmission Fan Relay Circuit Open Or Shorted. The transmission cooling fan control circuit has detected an open or shorted condition in the relay driver, relay coil, or associated wiring. This may result in the cooling fan failing to activate under high transmission fluid temperature conditions.
🚨 Repair Difficulty Tier
Tier: [DIY / Beginner]
This fault typically involves a relay swap test, visual wiring inspection, and basic electrical continuity checks. Diagnosis may require a digital multimeter and scan tool access. Connector and wiring repairs may require intermediate skills depending on harness location.
🛠️ Resolution Steps
Step 1: Preliminary Inspection
- Verify the active DTC and freeze frame data with a scan tool; record transmission fluid temperature at the time of the fault.
- Inspect the transmission cooling fan relay in the power distribution center (underhood fuse/relay box) for signs of heat damage, corrosion, melted sockets, or loose terminals.
- Visually inspect the fan circuit harness and connectors for chafing, pinched wires, moisture intrusion, or pin tension issues, paying close attention to areas near the radiator core support and fan shroud where harnesses flex.
- Check the relay-feed fuse in the power distribution center for continuity and confirm battery voltage is present at the relay common/power terminal using a digital multimeter referenced to chassis ground (should read battery voltage, approximately 12-14V key on, engine off).
- Confirm the fan assembly is mechanically free to rotate by hand and has no physical obstruction, debris, or seized bearing causing excessive current draw.
Step 2: Diagnostic Verification
- Perform a relay swap test using a known-good identical relay (often interchangeable with other body control relays of the same part number/style) to determine if the fault follows the relay.
- Command the transmission cooling fan on with a bi-directional scan tool and monitor the relay control circuit response for a change in commanded state versus actual state.
- Measure control circuit voltage at the relay control pin (coil trigger side) with the key on and the relay commanded on; verify the PCM/TCM driver is pulling the circuit to near-ground (low-side driver) or supplying reference voltage (high-side driver), consistent with standard relay-driver logic.
- Check control circuit continuity to ground and to battery voltage to identify a short condition, referencing the factory wiring diagram and connector pinout for the specific model year to correctly identify the control wire versus the power and ground wires at the relay socket.
- Measure fan motor ground and power supply circuits for excessive voltage drop under load (should typically be less than 0.5V drop across any single connection or ground point when fan is operating).
- Verify the Powertrain Control Module or Transmission Control Module software calibration is current and check for any applicable Technical Service Bulletins (TSBs) related to transmission cooling fan relay logic or software updates.
Step 3: Resolution & Reset Process
- Replace the faulty relay, repair the open or shorted wiring section using proper solder-and-heat-shrink or crimp-and-seal connectors, or replace the cooling fan assembly as indicated by test results.
- Ensure all connectors are fully seated, locked, and free of corrosion; apply dielectric grease to connector terminals where specified to prevent future moisture intrusion.
- Clear all stored diagnostic trouble codes using the scan tool and perform a KAM (Keep Alive Memory) reset if applicable by cycling the ignition or disconnecting the battery for the manufacturer-specified duration.
- Perform a road test or bi-directional fan command test to confirm correct fan operation (audible/visual fan activation) and no returning fault codes after a full drive cycle.
- Verify transmission fluid temperature readings return to normal operating range (typically below 220°F / 104°C under normal driving) during the test drive and that the cooling fan cycles appropriately under simulated load conditions.
📦 Parts, Labor, and Budget Estimates
Required Components/Software:
- Transmission cooling fan relay (standard automotive ISO/Micro relay, dealer or aftermarket OEM-equivalent part)
- Wiring repair kit (marine-grade heat-shrink butt connectors, loom tape, terminal pins) or partial harness section if damage is extensive
- Cooling fan assembly/motor (if motor or fan clutch has failed electrically or mechanically)
- Dielectric grease and terminal repair supplies
- Factory diagnostic software subscription (e.g., manufacturer-specific scan tool access) for PCM/TCM software verification or reflash, if a TSB applies
Average Component Price:
- Relay: $15 – $45 (dealer OEM) / $8 – $25 (aftermarket)
- Wiring repair materials: $20 – $75 depending on connector complexity and harness accessibility
- Cooling fan assembly (motor/shroud unit, if required): $150 – $450 depending on model and whether it is a standalone motor or complete assembly
- PCM/TCM reflash/software update (if performed at dealer): $100 – $250 in diagnostic/programming fees
Estimated Labor Hours:
- Diagnostic time (scan tool retrieval, relay swap, circuit testing): 0.5 – 1.5 hours
- Component replacement time (relay swap is typically under 0.2 hours; wiring repair 0.5 – 1.5 hours depending on access; fan assembly replacement 1.0 – 2.5 hours depending on model and whether front-end/bumper cover removal is required): 0.2 – 2.5 hours
- Verification, DTC clearing, and road test confirmation: 0.3 – 0.5 hours
- Total estimated shop time: approximately 1.0 – 4.0 hours depending on root cause severity (simple relay swap vs. full fan assembly and harness repair)