Corroded, loose, or damaged electrical connector at the ECT sensor; Chafed or broken wires in the ECT sensor circuit, often near the engine block or harness bends; Failing ECT sensor that intermittently opens or shorts internally when hot or vibrating; Poor ground connection for the ECT sensor circuit at the engine or chassis; Coolant contamination or low coolant level causing the sensor to read erratically; Faulty ECM, though this is rare and should only be suspected after all other causes are ruled out

DTC codes / Mazda codes / P1117

P1117 · MazdaECT Sensor Signal Intermittent

Q: What does code P1117 mean?

ECT Sensor Signal Intermittent. P1117 on a Mazda indicates that the engine control module (ECM) has detected an intermittent fault in the electrical circuit of the engine coolant temperature (ECT) sensor. The ECM monitors the sensor's signal voltage and flags this code when the reading momentarily drops out or jumps erratically, rather than failing completely like a hard circuit fault would.

P1117 on a Mazda indicates that the engine control module (ECM) has detected an intermittent fault in the electrical circuit of the engine coolant temperature (ECT) sensor. The ECM monitors the sensor's signal voltage and flags this code when the reading momentarily drops out or jumps erratically, rather than failing completely like a hard circuit fault would.

SystemPowertrain

Code typeMazda specific

SeverityMedium

Fix difficultyIntermediate

AreaFuel and air metering

Symptoms you may notice

Illumination of the check engine light, often with no other noticeable symptoms
Intermittent or erratic temperature gauge readings on the dashboard
Poor fuel economy or rough running when the engine is cold, due to incorrect fuel enrichment
Occasional hard starting or stalling when the engine is cold
Cooling fan running constantly or not engaging at the correct temperature
A slight hesitation or surge during acceleration when the ECM receives a faulty temperature signal

Common causes, most likely first

Corroded, loose, or damaged electrical connector at the ECT sensor
Chafed or broken wires in the ECT sensor circuit, often near the engine block or harness bends
Failing ECT sensor that intermittently opens or shorts internally when hot or vibrating
Poor ground connection for the ECT sensor circuit at the engine or chassis
Coolant contamination or low coolant level causing the sensor to read erratically
Faulty ECM, though this is rare and should only be suspected after all other causes are ruled out

How to diagnose and fix it

Inspect the ECT sensor connector for corrosion, tightness, and bent pins; clean or repair as needed
Perform a wiggle test on the ECT sensor harness while watching live data to catch intermittent opens
Check the ECT sensor resistance with a multimeter at various temperatures and compare to Mazda specifications
Verify the sensor's ground circuit has less than 1 ohm resistance to the engine block
Backprobe the ECT signal wire at the ECM and monitor voltage for dropouts while driving over bumps
Replace the ECT sensor if resistance testing or live data shows erratic behavior
Clear the code and perform a road test to confirm the repair, monitoring ECT live data for stability

Intermittent ECT faults that fool many technicians

A common mistake is replacing the ECT sensor immediately, but the intermittent signal often comes from a corroded connector pin or a chafed wire that only acts up when the engine bay is hot or vibrating.
The ECT sensor shares its ground reference with other sensors on many Mazda engines, so a poor ground can cause multiple intermittent codes and misleading live data.
Low coolant or air pockets around the sensor can cause the sensor to read erratically, mimicking an electrical fault, especially after cooling system work.
P1117 can set without ever turning on the check engine light if the intermittent fault is brief; some Mazda models store it as a pending code first.
Aftermarket ECT sensors with incorrect resistance curves are a frequent cause of repeat intermittent codes even when the wiring is perfect.

Can I keep driving with P1117?

You can usually continue driving with P1117, but avoid long trips or heavy loads until it is diagnosed, because an intermittent coolant temperature signal can cause poor fuel economy, rough cold running, and cooling fan malfunctions. If the temperature gauge behaves erratically or the engine overheats, stop driving and have it inspected immediately.

Tools that help

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Guidance is general and written for Mazda vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.