Ford Power Stroke · Engine Coolant Temperature SensorModerate

Ford Power Stroke 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 on your Ford Power Stroke means the coolant temperature sensor signal is stuck at an abnormally low voltage — usually from a short to ground in the wiring or a failed sensor. Check the connector and harness before swapping the sensor.

Overview: Ford Power Stroke P-Code P0117

P0117 is a straightforward electrical fault — the CTS signal wire is reading too low for the ECM to trust. ProfessionalDieselRepair.com checks the wiring and connector first on every P0117 call because a sensor swap into a shorted harness just sets the code right back.

Repair Snapshot

Time

0.5 - 1.5 Hours

Difficulty

Beginner

Parts Cost

$15 - $60

Dealer Labor

$100 - $250

Tools Required

  • Jaltest Diagnostic System
  • Texa Diagnostic Tool
  • Multimeter

What P-Code P0117 Means

P0117 on the Ford Power Stroke means the ECM received a voltage signal from the coolant temperature sensor (CTS) that was too low — below the normal operating range — indicating a short to ground on the signal wire or a failed sensor pulling the circuit down. Unlike P0116 (plausibility range/performance), P0117 is a true electrical fault. The ECM substitutes a default coolant temperature value, which can affect glow plug on-time, fuel trim, and EGR scheduling. ProfessionalDieselRepair.com treats this as a wiring and connector check before a sensor swap.

Symptoms Drivers Notice

  • Check engine light on
  • Extended glow plug on-time (ECM substitutes a cold default temperature)
  • Possible hard start in cold conditions if the ECM assumes the engine is always cold
  • Slightly elevated fuel consumption from a cold-bias fuel trim
  • No immediate derate but EGR and emission system behavior is affected

Most Likely Root Causes

Shorted or damaged CTS signal wire

Common

Heat damage or chafing causes the signal wire insulation to fail and short to ground, pulling the signal voltage below the normal operating range.

Failed coolant temperature sensor (internal short)

Common

The sensor itself can develop an internal short that mimics a wiring fault and pulls the signal circuit low.

Coolant contamination in the CTS connector

Occasional

On 6.0L Power Strokes with EGR cooler issues, coolant vapor or liquid wicking into the connector creates a conductive short path to ground.

Corroded or backed-out CTS connector pin

Occasional

A partially seated pin on the signal circuit can create an intermittent low-resistance short to the connector body.

Common Misdiagnoses (Don't Waste Parts)

Replacing the coolant temperature sensor as a parts-cannon first move without testing the signal wire for a short to ground

Why it happens: CTS replacement is cheap and easy, so it gets swapped first — but if the harness is shorted, the new sensor sets P0117 again within minutes of starting the engine.

Do this instead: Unplug the sensor and check for 5V reference on the signal wire. If you see near 0V with the sensor disconnected, the fault is in the wiring, not the sensor.

Missing coolant contamination in the connector from a seeping EGR cooler on 6.0L trucks

Why it happens: The EGR cooler connection to the CTS circuit isn't obvious, so the coolant-in-connector source gets overlooked.

Do this instead: Smell and inspect the connector for sweet residue or moisture before replacing any parts — coolant contamination in the connector indicates a bigger cooling system problem upstream.

Master Tech Commentary

Mechanic's Notes

Shop tip: ProfessionalDieselRepair.com always checks the connector and harness before ordering a sensor on P0117. On the 6.0L Power Stroke, a leaking EGR cooler can push coolant mist into the CTS connector and short it to ground — if the connector smells sweet or shows residue, investigate the EGR cooler before just swapping the sensor. Sensor replacement is straightforward and inexpensive, but wiring a new sensor into a shorted harness just sets the code again.

Step-by-Step Diagnostic Procedure

  1. Step 1: Connect Jaltest or Texa and pull the P0117 with freeze-frame data. Note the coolant temp reading at the time of fault — it will likely show an implausibly low value such as -40°F even on a warm engine.
  2. Step 2: With a multimeter, measure the signal wire voltage at the ECM harness connector (with the sensor unplugged). You should see approximately 5V reference on the signal wire. A reading of near 0V with the sensor disconnected confirms a short to ground in the wiring harness.
  3. Step 3: Inspect the CTS wiring harness and connector for damage, water intrusion, or chafing against a hot exhaust component. On 6.0L and 6.4L Power Strokes, the CTS connector is exposed to significant heat near the front of the engine.
  4. Step 4: Unplug the CTS and measure sensor resistance between its two terminals at a known coolant temperature. Compare to the published resistance curve — out-of-range resistance at a known temperature confirms sensor failure.
  5. Step 5: Check for coolant contamination in the CTS connector — coolant leaks from a seeping EGR cooler or head gasket on 6.0L trucks can wick into the connector and short the circuit.
  6. Step 6: After any repair, clear codes with Jaltest or Texa and verify the coolant temp PID reads a plausible value and tracks normally through warm-up.

Live Data & Freeze-Frame Tips

Watch the coolant temperature PID in Jaltest or Texa live data from a cold start. A healthy sensor will show a value close to ambient at startup and climb steadily through warm-up to approximately 195–210°F. A P0117 condition will show -40°F (pegged low) or an implausibly low static value with no warm-up movement.

Safety Warnings

  • Allow the engine to cool completely before removing the CTS — the sensor threads into a coolant passage and removing it on a hot engine releases scalding coolant.
  • Have a catch container ready when unplugging the CTS on a warm engine — some coolant drips from the sensor port.

When to Limp In vs Tow

P0117 alone does not require towing. The truck is drivable but the ECM is using a substitute coolant temperature value. If the code is accompanied by an actual overheating condition or a coolant leak, stop driving immediately.

Prevention Tips for Fleets & Owner-Operators

  • Inspect the CTS connector for corrosion or moisture during every coolant service.
  • Address any EGR cooler or head gasket seeping on 6.0L Power Strokes before coolant vapor has a chance to contaminate electrical connectors.
  • Use dielectric grease on the CTS connector when reassembling to slow future corrosion.

Related Fault Codes

Frequently Asked Questions

Is P0117 the same as P0118 on a Power Stroke?

No. P0117 is a circuit LOW input — signal voltage is too low, indicating a short to ground. P0118 is a circuit HIGH input — signal voltage is too high, indicating an open circuit or short to power. The diagnostic approach differs between the two.

Can I drive my Power Stroke with P0117?

Yes, the truck is drivable but the ECM is substituting a default coolant temperature value. Extended glow plug times and slightly off fuel trims are the main effects. Repair it within a week to restore accurate engine management.

How hard is it to replace the coolant temperature sensor?

It's one of the simpler jobs on a Power Stroke — usually a one-socket removal on a cooled engine, then thread in the new sensor with fresh thread sealer. Budget 30 minutes and minimal tools.

Why does my Power Stroke show -40°F coolant temp with P0117?

-40°F is the default pegged-low value the ECM reports when the coolant temp signal is outside its operating range. It doesn't mean your engine is actually at -40°F — it means the signal voltage is shorted low and the ECM has clamped its reading to the bottom of the scale.

Could P0117 cause my Power Stroke to run rich?

Yes. With the ECM believing the engine is perpetually cold, it enriches fuel delivery and extends glow plug on-time as it would during a cold start. This slightly increases fuel consumption and can affect emissions.

Does P0117 affect the EGR system on a Power Stroke?

Yes — EGR scheduling is influenced by coolant temperature. With a false cold-temperature signal, EGR operation may be reduced or delayed, slightly affecting emissions compliance and combustion characteristics.