🚨 Diagnostic Profile
Vehicle Make: Dodge
Description: Low Speed Fan Control Relay Circuit Open or Shorted. The powertrain control module has detected an electrical fault in the low speed cooling fan relay control circuit, which may cause the cooling fan to fail to engage at low speed, leading to engine overheating or a related warning condition.
🚨 Repair Difficulty Tier
Tier: [Intermediate]
Relay replacement is simple, but diagnosing an open or shorted control circuit requires a multimeter, wiring diagram access, and familiarity with PCM output driver behavior. Wiring repairs in the engine bay add moderate complexity.
🛠️ Resolution Steps
Step 1: Preliminary Inspection
- Verify battery state of charge and check for any active battery or charging system codes, since low voltage can mimic an open relay control circuit.
- Visually inspect the low speed fan relay location in the Totally Integrated Power Module (TIPM) or underhood power distribution center, consulting the fuse box lid legend to confirm correct cavity identification for this specific application.
- Inspect the relay socket terminals for corrosion, burn marks, loose pins, or heat discoloration, which is common on Dodge TIPM-controlled fan circuits due to high current cycling.
- Inspect the cooling fan harness and connectors near the shroud and radiator support for chafing, pinched wires, melted insulation, or water intrusion.
- Check the fan motor and fan assembly for physical obstruction, seized bearings, or a blown fan motor fuse in the TIPM.
- Record all active and stored diagnostic trouble codes and freeze frame data before clearing anything, noting whether the fault is active (hard fault) or stored (intermittent).
Step 2: Diagnostic Verification
- Confirm the fault with a scan tool capable of bi-directional control by commanding the low speed fan relay on and off through an actuator test while monitoring relay state feedback and listening/feeling for relay click and fan response.
- With the relay removed, measure control circuit continuity and resistance from the PCM driver pin to the relay control terminal in the relay socket using the vehicle-specific wiring diagram to positively identify the control circuit versus the coil power and switched output circuits; do not guess pin numbers from memory, pull the factory diagram for the exact circuit.
- Check for a short to ground in the control circuit by disconnecting the PCM connector (ignition off, battery disconnected per OEM procedure) and measuring resistance from the control circuit wire to chassis ground; a reading near zero ohms indicates a short to ground.
- Check for a short to voltage in the control circuit with the ignition on and the PCM disconnected by probing the control circuit wire with a digital multimeter referenced to ground; any unexpected voltage present indicates a short to a powered circuit.
- Verify relay coil supply (battery) voltage and switched power feed at the relay socket using a test light or multimeter referenced to a known good ground, and measure relay coil resistance out of circuit against the relay manufacturer specification.
- Test relay contact operation and voltage drop across the switched output circuit under load using the minimum voltage drop method, flagging any drop exceeding approximately 0.2V as excessive resistance.
- Inspect PCM and TIPM ground circuits and power feeds for corrosion or elevated resistance, as poor grounds are a frequent root cause of intermittent relay driver faults on this platform.
Step 3: Resolution & Reset Process
- Replace the low speed fan relay if coil resistance, contact resistance, or switched voltage drop tests fall outside specification.
- Repair any open, chafed, or shorted wiring using OEM-approved heat-shrink butt or solder splice connectors with proper gauge-matched wire, or replace the affected harness section per OEM service procedures; avoid crimp-only connectors in high-vibration engine bay locations.
- Replace any damaged relay socket terminals or connector housings, ensuring correct terminal tension and full seating to prevent repeat burnt-pin failures.
- Clear diagnostic trouble codes with a scan tool, then perform a key-cycle relearn and a road test or extended idle operational test to confirm both low speed and high speed fan operation across normal and A/C-on conditions.
- Verify that no codes return after the cooling system completes a full heat cycle and the A/C compressor has cycled on to confirm both fan speed outputs function correctly.
📦 Parts, Labor, and Budget Estimates
Required Components/Software:
- Low speed cooling fan relay (OEM or OEM-equivalent Bosch/Omron 4-pin or 5-pin micro relay, application-specific to engine and TIPM configuration)
- Relay socket pigtail or TIPM connector terminal repair kit if burnt terminals are found
- Wiring repair materials: heat-shrink butt splice connectors, OEM-gauge primary wire, electrical tape, split loom as needed (typically a small kit covering 1-2 splice repairs)
- OEM-level scan tool (e.g., Snap-on, Autel, or dealer-level diagnostic software) with bi-directional control and current software calibration to run actuator tests and verify PCM output driver status
- Digital multimeter and access to factory wiring diagrams (subscription service such as Mopar TechAuthority or equivalent)
Average Component Price:
- Relay: approximately $15 to $45 depending on OEM versus aftermarket and whether sourced individually or as part of a TIPM relay kit
- Connector or socket terminal repair kit: approximately $20 to $60
- Wiring repair materials: approximately $10 to $30 for splice connectors, wire, and loom
- TIPM replacement if internal relay driver circuit itself is found faulty (uncommon but possible): approximately $400 to $700 including module and required programming
- Total parts estimate (relay and wiring repair only, most common scenario): approximately $45 to $135
Estimated Labor Hours:
- Diagnostic time: approximately 0.8 to 1.5 hours shop book time for circuit tracing, relay testing, and PCM driver verification
- Relay or wiring repair time: approximately 0.3 to 0.5 hours for simple relay swap; 1.0 to 2.0 hours if a harness splice or connector repair is required
- Verification and reset time: approximately 0.3 to 0.5 hours for code clearing, actuator test confirmation, and road test or heat cycle verification
- Total labor estimate: approximately 1.4 to 4.0 hours depending on whether the repair is a simple relay replacement or involves wiring/connector repair; at typical shop labor rates of $120 to $170 per hour, total labor cost ranges from approximately $170 to $680
- Combined total repair estimate (parts and labor, most common relay/wiring scenario): approximately $200 to $650; TIPM replacement scenario (less common) could push total cost to $700 to $1100 including programming