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DTC codes / P0Exx · Hybrid propulsion / P0E7D

P0E7DAuxiliary Cooling Coolant Temperature Sensor A Circuit Low

P0E7D means the powertrain control module (PCM) has detected a low-voltage signal on the auxiliary cooling coolant temperature sensor A circuit, which is used to monitor the temperature of a secondary cooling loop such as a battery, inverter, or electric motor coolant circuit. The PCM expects the sensor's signal voltage to stay within a calibrated range, and a sustained low reading indicates a short to ground, a faulty sensor, or a wiring problem rather than a normal cold condition.

SystemPowertrain
Code typeGeneric (all makes)
SeverityMedium
Fix difficultyIntermediate
AreaHybrid propulsion

Symptoms you may notice

  • Illumination of the check engine light or service vehicle soon message with no other noticeable change in vehicle behavior.
  • Reduced or disabled auxiliary cooling pump operation, which may lead to overheating of high-voltage components in electric and hybrid vehicles.
  • A warning message on the dash indicating a cooling system fault or reduced power mode.
  • Inconsistent cabin heating or cooling performance if the auxiliary loop shares a heat exchanger with the climate system.
  • In rare cases, the vehicle may enter a limp-home mode that limits speed or power output to protect temperature-sensitive components.

Common causes, most likely first

  1. A failed auxiliary cooling coolant temperature sensor that internally shorts to ground and pulls the signal voltage low.
  2. A chafed or pinched sensor signal wire shorting to chassis ground along the harness routing.
  3. Corrosion or water intrusion at the sensor connector or PCM connector causing a low-resistance path to ground.
  4. A faulty PCM driver circuit that incorrectly reads or pulls the signal line low, though this is less common.
  5. Coolant contamination or sludge coating the sensor tip and altering its resistance characteristics.
  6. An aftermarket accessory or improper previous repair that tapped into the sensor circuit and introduced a ground fault.

How to diagnose and fix it

  1. Connect a scan tool and record the freeze-frame data for P0E7D, then clear the code and verify whether it returns immediately or only after a drive cycle.
  2. Visually inspect the auxiliary coolant temperature sensor, its connector, and the harness for chafing, corrosion, or coolant residue, repairing any obvious damage.
  3. Measure the sensor's resistance with a multimeter and compare it to the manufacturer's temperature-resistance chart to confirm whether the sensor is internally shorted.
  4. Back-probe the sensor signal wire at the PCM and check for a short to ground with the sensor disconnected, isolating whether the fault is in the wiring or the sensor.
  5. If the wiring and connector are intact, replace the auxiliary cooling coolant temperature sensor and clear the code.
  6. After any repair, run the vehicle through a complete drive cycle with the auxiliary cooling pump commanded on, monitoring live sensor data to confirm the signal stays within range.
  7. If the code persists with a known-good sensor and verified wiring, diagnose the PCM circuit or consult a dealer-level scan tool for advanced circuit testing.

Auxiliary coolant sensor low-voltage traps

  • A low signal voltage does not always mean the sensor has failed; a simple unplugged connector or a wire rubbed through on a bracket can set this code just as easily.
  • On many hybrid and electric vehicles, the auxiliary cooling loop serves the high-voltage battery and power electronics, so ignoring this code can lead to costly thermal damage rather than just a warning light.
  • Technicians often replace the sensor only to find the connector pins are pushed back or corroded, so always perform a pin drag test and inspect the terminals before condemning the sensor.
  • This code can be set by a low coolant level or air pocket that prevents the sensor from contacting liquid, even though the circuit itself is electrically sound.
  • A generic scan tool may show the auxiliary coolant temperature as a fixed low value, but manufacturer-specific live data is needed to see whether the PCM is commanding the cooling pump and what the actual sensor voltage is.

Can I keep driving with P0E7D?

You can usually drive the vehicle short distances to a repair shop, but avoid heavy loads, long trips, or aggressive driving because the auxiliary cooling system may not be operating correctly. If the dash displays a high-voltage battery temperature warning or reduced power message, stop driving and have the vehicle towed to prevent damage to expensive components.

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 all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

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