Ram Cummins · Engine Coolant Temperature SensorMedium

Ram Cummins P0117: Engine Coolant Temperature Circuit Low Input

P-Code P0117 (FMI N/A) — Engine Coolant Temperature Circuit Low Input

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Quick Answer

P0117 means the coolant temperature sensor circuit is shorted to ground, causing a falsely low reading. It's a medium-severity electrical fault that can affect fueling and fan operation - pin test the harness before replacing the sensor.

Overview: Ram Cummins P-Code P0117

This is a genuine electrical short, distinct from the plausibility-based P0116 code. ProfessionalDieselRepair.com always traces the signal wire for contact with a grounded surface near the engine block first, since that's a more common cause than an actually failed sensor.

Repair Snapshot

Time

45 Minutes - 1.5 Hours

Difficulty

Beginner

Parts Cost

$25 - $150

Dealer Labor

$260+

Tools Required

  • Cummins INSITE
  • Diesel Laptops Scan Tool
  • Multimeter

What P-Code P0117 Means

P0117 means the coolant temperature sensor circuit is reading a voltage lower than expected, consistent with a short to ground. Unlike the plausibility-based P0116, this is a true electrical fault - the ECM defaults to an assumed high coolant temperature, which can affect fueling and fan operation.

Symptoms Drivers Notice

  • Check engine light with cooling fan possibly running constantly
  • Poor heater output since the ECM thinks the engine is already hot
  • Possible rich-running condition affecting fuel economy
  • No major drivability complaint in most cases

Most Likely Root Causes

Signal wire shorted to a grounded engine surface

Common

A chafed wire contacting the engine block or another grounded component pulls the signal voltage down to near zero.

Internally shorted sensor

Occasional

A sensor with an internal short can present the same low-voltage signature as a wiring fault.

Corroded connector causing a partial short

Occasional

Moisture intrusion at the connector can create a path to ground that produces a similar low-reading fault.

Common Misdiagnoses (Don't Waste Parts)

Replacing the sensor without pin-testing the harness

Why it happens: The sensor is a fast parts-cannon swap that skips the cheaper wiring inspection.

Do this instead: Back-probe the harness with the sensor disconnected - a reading still near 0V confirms the fault is in the wiring, not the sensor.

Master Tech Commentary

Mechanic's Notes

Shop tip: ProfessionalDieselRepair.com always pin-tests this circuit before replacing the sensor - a wire shorted to a grounded surface near the engine block is a more common cause than an actually failed sensor element.

Step-by-Step Diagnostic Procedure

  1. Step 1: Pull the fault and freeze-frame coolant temperature data with Cummins INSITE - a value pinned at an unrealistic low reading confirms the short-to-ground condition.
  2. Step 2: Locate the coolant temperature sensor and unplug the connector.
  3. Step 3: Back-probe signal and ground with a multimeter, key on engine off - a reading near 0V with the sensor disconnected confirms a harness-side short to ground.
  4. Step 4: Trace the signal wire for chafing against the engine block, exhaust manifold, or other grounded surfaces.
  5. Step 5: Test sensor resistance at the connector against the OEM temperature/resistance chart to rule out an internally shorted sensor.
  6. Step 6: Repair the wiring or replace the sensor as needed, then clear the code and confirm a plausible reading returns.

Live Data & Freeze-Frame Tips

With the sensor connected, coolant temperature should track a plausible warm-up curve from cold start to operating temperature. A value stuck near the sensor's minimum output (an unrealistically hot reading) confirms the short-to-ground fault.

Safety Warnings

  • Allow the engine to cool before accessing the coolant temperature sensor near the engine block.
  • Disconnect the battery before repairing any chafed wiring.

When to Limp In vs Tow

No towing is required for this code alone - it's a low-severity electrical fault that doesn't affect safe driving.

Prevention Tips for Fleets & Owner-Operators

  • Route and secure wiring away from the engine block and other grounded surfaces.
  • Inspect connector pins for corrosion during routine PM services.
  • Address any minor sensor circuit warnings promptly before they progress.

Related Fault Codes

P0118

Engine coolant temperature circuit high input - the opposite electrical fault, a short to power instead of a short to ground.

P0116

Engine coolant temperature circuit range/performance - a plausibility mismatch fault, distinct from this true electrical short.

Frequently Asked Questions

Can I drive with this code active?

Yes, this code doesn't trigger a derate or shutdown, though you may notice the cooling fan running more than usual and reduced heater output.

How do I reset this code without a scanner?

Use Cummins INSITE or Diesel Laptops to clear the code once the wiring or sensor repair is verified.

Why does the ECM think my engine is hot when it's not?

A short-to-ground pulls the sensor voltage down, which the ECM interprets as an implausibly high coolant temperature reading.

Is the sensor usually the problem, or the wiring?

A wire shorted to a grounded surface near the engine block is a more common cause than an actually failed sensor element.

Will this affect fuel economy?

It can, since the ECM may run a richer fuel mixture believing the engine is already at operating temperature.

Will my cooling fan run constantly with this code?

It's possible, since the ECM sees an implausibly high coolant temperature reading and may respond by running the fan more aggressively.