🚨 Diagnostic Profile
Vehicle Make: Dodge
Fault Description: Radiator Temperature Sensor Voltage Too High. This is typically associated with the engine coolant temperature (ECT) sensor circuit reading above its expected range, commonly logged as generic OBD-II code P0118 (ECT Circuit High Input). On most Dodge/Chrysler group vehicles, a high-voltage condition on this circuit indicates an open sensor signal circuit, an open ground circuit, a failed sensor (open internally), or a PCM that is not receiving a valid return signal. Exact code assignment and PCM pinout should be confirmed with a scan tool and factory wiring diagram for the specific model year and engine.
🚨 Repair Difficulty Tier
Tier: [Intermediate]
Sensor access and replacement are straightforward, but accurate diagnosis requires a scan tool with live data, a digital multimeter, and the ability to read wiring circuits. Wiring or connector faults may require additional diagnostic time.
🛠️ Resolution Steps
Step 1: Preliminary Inspection
- Verify the coolant level and condition in the reservoir and radiator, and confirm the cooling system is not overheating or low enough to expose the sensor tip to air.
- Scan for active and stored DTCs and record freeze-frame data, noting whether the fault is continuous or intermittent.
- Inspect the ECT sensor connector for corrosion, bent pins, moisture, or loose seating. On most Dodge/Chrysler engines, the ECT sensor is threaded into the cylinder head, intake manifold, or thermostat housing near the coolant crossover; confirm exact location using the engine-specific service manual or a parts diagram, as placement varies between the Pentastar V6, Hemi V8, and 4-cylinder Tigershark/GEMA engine families.
- Visually inspect the harness for chafing, heat damage, or pinching near the sensor, along the valve cover, and at firewall grommet pass-throughs.
- Check for aftermarket accessories, remote starts, or previous collision/engine repairs that may have affected the sensor circuit or connector routing.
Step 2: Diagnostic Verification
- Review live data for ECT values (°F/°C) and compare against actual coolant temperature using an infrared thermometer at the thermostat housing as a cross-reference.
- With the key on, engine off and the connector disconnected from the sensor, measure the reference voltage supplied by the PCM at the sensor signal circuit using a digital multimeter back-probed against a known good chassis ground. Confirm the presence of a stable reference voltage (typically 5V sensor reference circuits are used on these systems); an open or very high reading with the sensor unplugged is normal and confirms the PCM side of the circuit is intact.
- With the connector still disconnected, measure sensor resistance directly across the two sensor terminals using an ohmmeter. ECT/IAT-type thermistors are negative temperature coefficient (NTC) devices — resistance should be high when cold and decrease steadily as the sensor warms (verify exact resistance-to-temperature values against factory service information for the specific engine, as values vary by sensor design). An infinite or open reading at any temperature indicates a failed sensor.
- Check the sensor ground/return circuit for continuity and resistance to a verified engine ground; resistance should be near zero ohms. High resistance or an open circuit here will cause an artificially high voltage reading at the PCM, triggering a High Input code even with a good sensor.
- Inspect and wiggle-test the harness and connector while monitoring live data for signal dropout, which indicates an intermittent open circuit rather than a failed sensor.
- Confirm the sensor reads a plausible value at cold start (close to ambient temperature) and climbs smoothly to normal operating range (typically 195–220°F) after warm-up without erratic spikes or dropouts.
- Clear codes and perform a road test through multiple heat cycles to confirm whether the fault returns.
Step 3: Resolution & Reset Process
- If the sensor is out of specification, shows an open circuit, or is reading erratically, replace the ECT sensor and apply the correct thread sealant (typically a factory-specified coolant-safe thread sealant) or new O-ring/sealing washer as specified by the manufacturer — do not use Teflon tape on sensors with electrical grounding through the threads.
- If the harness or connector is damaged, repair the affected section using OEM-approved weatherproof splice connectors and proper terminal crimping tools; do not solder-only without adding strain relief and sealant in engine bay locations exposed to heat and moisture.
- Refill and bleed the cooling system per the manufacturer’s procedure (including use of the radiator bleed screw where equipped) to remove air pockets, which can cause false or erratic temperature readings and simulate sensor circuit faults.
- Clear all DTCs and perform a drive cycle sufficient to allow the PCM to run its ECT circuit rationality monitor and confirm no fault re-triggers.
- Re-scan the vehicle to confirm no pending, active, or stored codes remain and that live ECT data tracks smoothly with engine temperature through a full warm-up cycle.
📦 Parts, Labor, and Budget Estimates
Required Components/Software:
- Engine coolant temperature (ECT) sensor, OEM Mopar or quality aftermarket equivalent (Standard Motor Products, Motorcraft-equivalent, or Walker) — confirm exact part number by VIN/engine code at a dealer parts counter or parts catalog, as Dodge uses multiple distinct ECT sensor designs across V6, V8, and 4-cylinder platforms
- Sensor O-ring or factory-specified thread sealant, matched to sensor design
- Replacement coolant — Dodge vehicles typically require HOAT (Hybrid Organic Acid Technology) coolant such as Mopar OAT/HOAT or equivalent; verify correct formulation and mixture ratio for the specific model year, as using the wrong coolant chemistry can cause sensor and cooling system issues
- Connector terminals or weatherproof harness repair kit (if corrosion or chafing is found)
- Professional OBD-II scan tool with live data streaming and bidirectional control capability (e.g., Snap-on, Autel, or factory-level diagnostic software)
- Digital multimeter and infrared thermometer
Average Component Price:
- ECT sensor: $15 – $60 (part only, depending on OEM vs. aftermarket and engine platform)
- Coolant (per gallon/jug, concentrate or pre-mixed): $12 – $25 per gallon; most jobs require 1–2 gallons depending on system capacity
- Miscellaneous seals, sealant, and hardware: $5 – $15
- Harness repair kit/connector (if needed): $20 – $75
Estimated Labor Hours:
- Diagnostic time (scan, live data review, circuit testing): 0.5 – 1.5 hours
- Sensor replacement and coolant drain/refill/bleed service: 0.5 – 1.2 hours (higher end if sensor location requires intake or manifold component removal for access)
- Harness/connector repair (if required, in addition to above): 0.5 – 1.0 hour
- Verification road test and final re-scan: 0.3 – 0.5 hours
- Total shop book time: 1.0 – 3.0 hours depending on sensor accessibility and whether wiring repair is needed
Estimated Total Out-the-Door Cost (Parts + Labor): Approximately $120 – $350 at typical independent shop labor rates ($100–$170/hr), with dealer pricing potentially running higher; DIY cost is largely limited to parts and coolant, typically $25 – $90.