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Home / DTC / P0E84 — Auxiliary Cooling System Coolant Temperature Sensor A Circuit High

P0E84 — Auxiliary Cooling System Coolant Temperature Sensor A Circuit High

Detailed page for trouble code P0E84.

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P0E84

Generic P — Powertrain

Auxiliary Cooling System Coolant Temperature Sensor A Circuit High

Brand: Generic
Type: P — Powertrain
Views: UK: 7 EN: 18 RU: 13
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Page language: EN

Causes

  • Open or disconnected sensor wiring (broken conductor, pulled out terminal)
  • Corroded/poor connector or pin contact at sensor or ECM
  • Short to battery voltage or to the 5V reference supply
  • Failed coolant temperature sensor (internal open or high resistance)
  • Poor or missing ground at sensor circuit or ECM
  • ECM/input module fault (rare)

Symptoms

  • Check Engine MIL on; stored P0E84 (and possibly related codes)
  • Auxiliary cooling fan or pump for the auxiliary system may not run as commanded or may run incorrectly
  • Incorrect coolant temperature indication for auxiliary circuit (shows unusually low/cold or extreme readings)
  • Reduced cooling system performance, possible higher engine or component temperatures in affected circuit
  • Intermittent operation if wiring is loose or corroded

What to check

  • Read and record all stored codes and freeze-frame data with a scan tool; check pending/related codes
  • Inspect sensor connector and wiring for corrosion, bent pins, damaged insulation, or disconnection
  • With ignition ON (engine off), use a scanner to observe the auxiliary coolant sensor voltage/temperature PID values
  • Backprobe sensor connector and measure: reference voltage (should be ~5 V or specified reference), signal voltage, and ground continuity
  • Check continuity between sensor signal pin and ECM signal pin (look for opens)
  • Check for short to battery: measure voltage to battery positive at the signal wire with key on

Signal parameters

  • Typical reference voltage: ~5.0 V (varies by manufacturer)
  • ‘Circuit High’ signal voltage: typically > ~4.5 V (may approach reference voltage or open-circuit level)
  • Normal cold sensor signal voltage: high but within specified range (often 3.5–4.5 V); normal hot sensor voltage: low (often 0.2–1.2 V) — values vary by vehicle
  • Typical thermistor resistance examples (manufacturer dependent): at ~20 °C the sensor may be in the kiloohm range (e.g., ~1–5 kΩ); resistance falls as temperature rises — consult vehicle-specific data

Diagnostic algorithm

  1. Confirm code and gather context: read all codes, freeze frame and live PID for both engine and auxiliary coolant temperature sensors.
  2. Visual inspection: check sensor connector, pins, wiring harness routing, insulation damage, and nearby heat/chafe points.
  3. With ignition ON, engine OFF: backprobe sensor connector and measure: a) reference voltage from ECM (expect ~5 V), b) signal voltage (should not be stuck at reference/5 V), c) ground continuity to chassis/ECM ground.
  4. If signal is at or near reference voltage: disconnect sensor and measure signal wire voltage. If it remains at reference, suspect open sensor or open to ground. If it rises to battery voltage, check for short to 12 V.
  5. Measure resistance of the removed sensor at ambient temperature and compare to specification (or swap with a known-good sensor) to verify sensor integrity.
  6. Check continuity between sensor signal pin and ECM signal pin; repair any open circuits or damaged wiring. Repair short to power if present.

Likely causes

  • Open or corroded connector at the auxiliary coolant temperature sensor
  • Wiring damaged by chafing or heat leading to an open or short to 12V/5V
  • Failed auxiliary coolant temperature sensor (internal open/high resistance)
  • Poor ground or engine/vehicle ground strap affecting sensor reference

Fault status

⚠️ Status
Auxiliary Cooling System Coolant Temperature Sensor A — Circuit High. ECM detected signal voltage above expected range (open circuit or short to reference/power). May affect auxiliary cooling control.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 0.5-2.0 hours

Similar codes

P0115 P0117 P0118 P0119 P0128
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