P0117 on 2005-2014 Ford Mustang: Engine Temperature Sensor Circuit Low Causes and Fixes

What's Unique About the 2005-2014 Ford Mustang

The most critical detail for this code on the S197 Mustang is the type of sensor used. V6 models (4.0L and 3.7L) use a traditional Engine Coolant Temperature (ECT) sensor that sits in a coolant passage, usually on the thermostat housing. In contrast, the V8 models (4.6L 3V and 5.0L Coyote) do not have an ECT sensor; they use a 'dry' Cylinder Head Temperature (CHT) sensor that screws directly into the cylinder head metal. The PCM infers the coolant temperature from the CHT reading. While both sensor types serve the same function and can trigger a P0117 code, their location, part number, and replacement difficulty are vastly different, with the V8 CHT sensor being significantly more labor-intensive to replace.

Generation note: This guide covers the entire S197 Mustang platform, which includes two major iterations: - 2005-2010: These models came with either the 4.0L SOHC V6 (uses an ECT sensor) or the 4.6L 3V V8 (uses a CHT sensor). - 2011-2014: These models featured the updated 3.7L 'Cyclone' V6 (uses an ECT sensor) and the 5.0L 'Coyote' V8 (uses a CHT sensor). The primary difference regarding this code is always V6 vs. V8, not the model year.

Symptoms You May Notice

• Check Engine Light is on
• Temperature gauge reads abnormally high (often maxed out) or is completely dead.
• Cooling fans run constantly at full speed, even when the engine is cold.
• Poor fuel economy due to the engine running a rich fuel mixture in fail-safe mode.
• Engine is hard to start, especially when cold.
• Rough idle, hesitation, or reduced engine power ('limp mode').
• Air conditioning (A/C) compressor may not engage as the PCM tries to reduce engine load.
• Black smoke from the exhaust in some cases due to a rich fuel condition.

Most Likely Causes

1. Failed Engine Coolant Temperature (ECT) Sensor (V6 Models Only) 🔴 High Probability → Shop Engine Coolant Temperature Sensor The sensor is a simple thermistor that can fail over time due to thermal stress. On the 4.0L V6, it is located in a plastic thermostat housing which is also a known failure point for cracking and leaks.
   How to confirm: On the 4.0L V6, locate the sensor on the thermostat housing at the front of the engine. With a scan tool, check if the ECT reading is stuck at a very high temperature (e.g., 250°F+) when the engine is cold. Disconnecting the sensor should make the reading drop to its lowest possible value (e.g., -40°F) and set a P0118 code. If it does, the sensor is bad.
   Typical fix: Replace the ECT sensor and its retaining clip. This is a simple, low-cost DIY job. It's often wise to replace the plastic thermostat housing at the same time if it shows signs of aging or leaking. 🎬 See this step-by-step V6 thermostat housing replacement guide
   Est. part cost: $20-$50
2. Failed Cylinder Head Temperature (CHT) Sensor (V8 Models Only) 🔴 High Probability → Shop Engine Cylinder Head The sensor is located in a high-heat area under the intake manifold, making it and its wiring susceptible to heat-cycle fatigue and failure. This is a well-documented issue on both the 4.6L and 5.0L engines.
   How to confirm: Use a scan tool to check the CHT reading on a cold engine. If it shows an impossibly high temperature, the sensor or its circuit is faulty. A low voltage reading (under 0.2V) points to a short. This failure often occurs with code P1299 (Cylinder Head Overtemperature Protection Active).
   Typical fix: Replace the CHT sensor. This is a labor-intensive job. On the 4.6L 3V, the sensor is on the driver's side head behind the alternator. On the 5.0L Coyote, it's on the rear of the passenger side cylinder head near the firewall. Both typically require removing the intake manifold for access, which adds significant labor time and cost.
   Est. part cost: $25-$60
3. Shorted Wiring or Damaged Connector 🟡 Medium Probability Engine heat can make the wiring harness brittle over time. On V8 models, the harness routing under the intake manifold is a common chafe point where wires can rub through and short to ground. Rodents are also known to chew on the soy-based wiring insulation used in this era, causing shorts. Manufacturer bulletin SSM 47791 notes that on similar Ford engines, P0117 can be caused by an ECT sensor connector that is not fully seated.
   How to confirm: Visually inspect the wiring leading to the ECT/CHT sensor for any signs of melting, chafing, or breaks. Unplug the sensor; if the P0117 code persists and a P0118 (High Input) does not appear, it strongly suggests the signal wire is shorted to ground somewhere in the harness.
   Typical fix: Repair the damaged section of the wire or replace the connector pigtail. This can be simple if the damage is accessible, or complex if it's under the intake manifold.
   Est. part cost: $10-$30 for a pigtail
4. Low Engine Coolant or Air in the System ⚪ Low Probability → Shop Engine Coolant / Antifreeze While this typically causes an overheating condition or a P0128 code, severe coolant loss on a V6 could expose the ECT sensor to air, causing erratic readings. This is less likely to cause a P0117 (short circuit) than a P0118 (open circuit). This cause is not applicable to V8 models with a dry CHT sensor.
   How to confirm: Check the coolant level in the degas (overflow) bottle when the engine is cool. If it's low, inspect for leaks from hoses, the radiator, or the thermostat housing.
   Typical fix: Top off the coolant and bleed the system of any air. Repair any leaks found.
   Est. part cost: $20-$40 for coolant

Rare But Worth Checking

• Faulty Powertrain Control Module (PCM): → Shop Engine Control Module (ECM) This is extremely rare. The PCM should only be considered as the cause after the sensor, connector, and all wiring have been thoroughly tested and confirmed to be good.

Diagnosis Steps

1. Check for Other Codes: Scan the PCM for any other stored codes, paying close attention to P0118 or P1299, to get a complete picture of the issue. TSB 21-2168 indicates that P0117 often appears alongside codes like P0116, P0119, P0128, and P1299 due to intermittent drops in the temperature signal.
2. Check Coolant Level (V6 Models): Ensure the engine coolant is at the proper level in the degas bottle (when cool). A low level will not cause P0117 on a V8.
3. Analyze Live Data: Use a scan tool to view the live data for the ECT (V6) or CHT (V8). If the engine is cold, the reading should be close to the ambient air temperature. A reading of 250°F or higher on a cold engine points directly to a circuit low/shorted condition.
4. Inspect the Sensor and Connector: Visually inspect the temperature sensor and its electrical connector for any obvious damage, corrosion, or loose wires. For V8s, this may require removing components to see the sensor harness.
5. Perform a Disconnect Test: With the scan tool still connected and displaying live data, disconnect the sensor. The temperature reading should immediately drop to a very low value (e.g., -40°F) and a P0118 code should set. If the temperature reading stays high, the fault is in the wiring harness (short to ground). If the reading drops as expected, the sensor itself is faulty.
6. Test the Wiring: If a wiring fault is suspected, use a digital multimeter to check for continuity to ground on the signal wire between the PCM and the sensor connector (with both ends disconnected). There should be no continuity to ground.
7. Test the Sensor (Optional): You can test the sensor's resistance with a multimeter. At room temperature (~68°F/20°C), it should read approximately 37k ohms. This resistance should decrease as the sensor is heated. A reading near zero ohms indicates a shorted sensor.
🎬 Watch: How to test and replace the coolant temperature sensor

Parts You'll Likely Need

• Engine Coolant Temperature (ECT) Sensor (V6 Models) (OEM #5R3Z-12A648-A (Motorcraft DY1146)) — This is the most common failure point for the P0117 code on 4.0L and 3.7L V6 engines. Replacement is simple and immediately resolves the issue if the sensor is the cause.
  Trusted brands: Motorcraft, Bosch, NTK, Delphi
  OEM price range: $30-$50
  Aftermarket price range: $15-$30
• Cylinder Head Temperature (CHT) Sensor (V8 Models) (OEM #4.6L 3V: 3L7Z-12A648-AA (Motorcraft DY1145) | 5.0L: BR3Z-12A648-A (Motorcraft DY1177)) — The most common failure for P0117 on V8s. Due to the high labor cost of replacement, it's critical to use a high-quality OEM or equivalent part to avoid repeating the job.
  Trusted brands: Motorcraft
  OEM price range: $35-$60
  Aftermarket price range: $25-$45

Related Codes That Often Appear With This One

• P0118 — P0118 is 'ECT Circuit High Input'. It can appear if the wiring issue is intermittent, switching between an open (P0118) and a short (P0117), or if a technician disconnects the sensor during diagnosis which creates an open circuit.
• P1299 — P1299 is 'Cylinder Head Overtemperature Protection Active'. This Ford-specific code is very often triggered on V8 models alongside P0117. The failed CHT sensor sends a false high-temperature signal, causing the PCM to activate its engine protection strategy.

Technical Service Bulletins (TSBs) & Recalls

• TSB 19-2049: While for 2019 models, this TSB addresses P1289 (CHT Circuit High) on 5.0L engines, it validates the CHT sensor as a known failure point and describes the diagnostic and repair process, which is highly relevant to the 2011-2014 5.0L engines experiencing similar codes like P0117.
• TSB 21-2168: This bulletin notes that vehicles may exhibit an illuminated MIL and Engine Coolant Over Temperature warning with DTC P0117, often caused by an intermittent drop in the engine coolant temperature (ECT) signal.
• SSM 47791: A manufacturer service bulletin stating that P0117 may be due to an engine coolant temperature (ECT) sensor connector which is not fully seated.

Platform-Specific Known Issues

• V8 CHT Sensor Location & Difficulty: The primary challenge on V8 models is accessing the CHT sensor. On the 4.6L 3V (2005-2010), it's under the intake manifold on the driver's side head, behind the alternator. On the 5.0L Coyote (2011-2014), it's even more difficult, located on the rear of the passenger-side head against the firewall. Both require removing the intake manifold, a 3-5 hour job.
• V6 ECT Sensor and Housing: → Shop Engine Coolant Temperature Sensor On V6 models, particularly the 4.0L, the plastic thermostat housing where the ECT sensor is mounted is prone to becoming brittle and cracking over time, causing coolant leaks. When replacing the ECT sensor, it is highly advisable to inspect and likely replace the entire housing assembly to prevent future leaks.

Mechanic-Grade Diagnostic Values

• CHT/ECT Sensor Resistance (Cold Engine) — expected: ~37,000 Ω (37 kΩ) @ 68°F (20°C). Failure: A resistance near 0 Ω indicates a shorted sensor, which directly causes P0117.
• CHT/ECT Sensor Resistance (Hot Engine) — expected: ~2,400 Ω (2.4 kΩ) @ 176°F (80°C) or ~1,180 Ω (1.18 kΩ) @ 212°F (100°C).. Failure: Resistance does not decrease as the engine warms, or the value is drastically different from the expected value for a known temperature.
• CHT/ECT Sensor Circuit Voltage (Key On, Engine Off, Cold) — expected: ~3.0V - 4.0V at the PCM, depending on ambient temperature.. Failure: A voltage below 0.2V indicates a short to ground in the wiring or a shorted sensor, triggering P0117.
• CHT/ECT Reference Voltage (Sensor Disconnected, Key On) — expected: ~5.0 Volts on one of the two pins in the connector harness.. Failure: No voltage or significantly less than 5.0V indicates a problem with the wiring or the PCM's 5V reference circuit.

Wiring & Ground Locations

• CHT Sensor Circuit (4.6L 3V V8) — The two CHT wires run to the main PCM connector (C175E). On similar Ford V8 platforms, these are often pins 41 (Signal) and 58 (Signal Return).. If the wiring harness under the intake manifold is damaged (a common issue), a technician can test for continuity directly from the sensor connector to these specific PCM pins to confirm a break or short without removing the manifold.
• G105 (4.6L 3V V8) — A major engine ground located on the bottom of the engine, near the starter motor.. While the CHT sensor uses a dedicated signal return to the PCM, a poor main engine ground can introduce electrical noise and voltage offsets into various sensor circuits, potentially causing erratic readings or contributing to fault codes.
• CHT Sensor Connector (V8 Models) — For the 4.6L 3V, it's behind the alternator. For the 5.0L, it's at the rear of the passenger cylinder head near the firewall.. The connector itself (pigtail) can become brittle from extreme heat and crack, or the locking tab can break, leading to a poor connection that mimics a sensor or wiring failure. The pigtail for the 4.6L 3V is often listed as Motorcraft WPT-117.

Real Owner Repair Stories

• Mustang Forums at StangNet user 'paintballpyro1' (1996 Mustang GT with a 2004 engine swap (likely 4.6L 2V)) — Car would not start on a cold morning, but started fine when warm. Code P0117 was present.
  ❌ Tried (didn't work) Initial diagnosis was uncertain due to multiple sensors on the intake crossover.
  ✅ What actually fixed it The connectors for the two coolant sensors on the intake manifold had been swapped. After correcting the connectors so each sensor was plugged into the correct harness, the P0117 code was resolved.
• NHTSA ODI #11613716 — An owner reported that code P0117 was pulled from their vehicle and was traced to concerns about overheating of the cylinder head causing cracks and leaks into the oil, noting that other recalls have been issued by the manufacturer for engine overheating.

Model Year Variations Within This Range

• 2005-2010 V8 vs 2011-2014 V8: The CHT sensor location is different. On the 4.6L 3V (2005-2010), the sensor is on the driver's side cylinder head, behind the alternator. On the 5.0L Coyote (2011-2014), it is on the rear of the passenger side cylinder head near the firewall, which is generally considered more difficult to access.

Diagnostic Flowchart

Other Known Issues on This Vehicle

Issues unrelated to this code that are worth knowing about as an owner of this generation:

• 4.6L 3V Spark Plug Breakage 🔴 High — Very common on 2005-2008 models with the original two-piece spark plug design. Occurs during removal. (Ref: Ford issued a TSB with a special procedure, but no recall. Requires a special extraction tool if they break.)
• Water Leaks into Cabin / Smart Junction Box (SJB) 🔴 High — Common across all years, especially 2005-2009. Clogged cowl drains or bad body grommets allow water to leak onto the SJB (fuse box) in the passenger footwell, causing major electrical problems. (Ref: TSB 08-26-7 addresses leaking body seam sealer and grommets.)
• Aluminum Hood Corrosion 🟠 Medium — Widespread on 2005-2009 models. Paint bubbles and peels along the leading edge of the hood due to contamination under the paint. (Ref: TSB 19-2026 (supersedes earlier versions) addresses this cosmetic issue, often requiring hood replacement.)
• MT-82 Manual Transmission Problems (2011-2014) 🟠 Medium — Common complaints on GT and V6 models with the Getrag MT-82 6-speed manual. Issues include high-RPM lockout, grinding shifts (especially 1-2), and premature clutch/slave cylinder failure.
• 4.0L V6 Plastic Thermostat Housing Failure 🔴 High → Shop Integrated Thermostat Housing Assembly — Extremely common on 2005-2010 V6 models. The plastic housing cracks, causing major coolant leaks. Often replaced with an aluminum aftermarket version.

Used vs. New Parts: Buying Guide for This Vehicle

When a used part is the smart pick: For this specific repair, using used parts is generally not recommended. The primary failure components (ECT/CHT sensor, wiring pigtail) are inexpensive, wear-prone electronic parts. The risk of a used sensor failing shortly after installation outweighs the small cost savings, especially for V8 models where replacement labor is extremely high.

Donor-vehicle mileage cap: roughly under 15000 miles for the part to have meaningful remaining life.

What to inspect on the donor part:

• If forced to use a used part, source it from the lowest-mileage donor possible.
• Inspect the plastic connector housing for any brittleness, cracking, or a broken locking tab.
• Check sensor threads for any signs of cross-threading or damage.

OEM-only on this vehicle (don't cheap out):

• Cylinder Head Temperature (CHT) Sensor (V8 Models)

Aftermarket brands forum-validated for this vehicle:

• NTK
• Bosch
• Delphi

Brands owners have reported issues with on this vehicle:

• No-name, unbranded 'white-box' sensors from online marketplaces should be avoided. The quality control is often poor, and failure rates are high, which is a significant risk given the labor involved in V8 sensor replacement.

Real Owner Stories

Aggregated from forums and TSBs cited above. Mileages and costs reflect what owners reported in those sources.

Related OBD-II Codes

• P0118 — The 'High Input' counterpart to P0117; it often appears if the sensor is disconnected or has an open circuit, whereas P0117 indicates a short to ground.
• P1299 — Cylinder Head Overtemperature Protection Active; this code frequently triggers alongside P0117 on V8 models when the CHT sensor signal indicates an extreme overheat condition.
• P1285 — Cylinder Head Over Temperature Condition; often stored with P0117/P1299 when the PCM detects the engine is operating above safe temperature limits.
• P0128 — Coolant Thermostat (Regulating Temperature Below Thermostat Regulating Temperature); related to cooling system efficiency and can be triggered by low coolant levels or a faulty thermostat housing on V6 models.
• P1289 — CHT Circuit High; a related temperature circuit code mentioned in TSB 19-2049 regarding 5.0L engine sensor failures.
• P0116, P0119, P0217, P0330, P1026 — These codes are noted in TSB 21-2168 as potentially appearing alongside P0117 due to intermittent engine coolant temperature signal drops.

Frequently Asked Questions