P1119 — Engine Coolant Temperature (ECT) Sensor Circuit Intermittent Low Voltage/IAT - B Circuit Low Input

For Ford vehicles

manifold air temperature circuit – signal too high

powertrain (engine/transmission)

Is it safe to drive?

Drive with caution Drive with caution and watch the temperature gauge. A thermostat stuck open mainly costs fuel; any sign of overheating means stop immediately — driving an overheating engine destroys head gaskets and worse.

How to diagnose with an OBD scanner

Read the code and freeze frame Connect an OBD2 scanner, confirm P1119 is stored, and save the freeze frame data — it shows engine conditions when the fault was detected.
Check for companion codes and TSBs Related codes often reveal the real root cause. Also check manufacturer technical service bulletins (TSB) for your make and model — many P0xxx issues have factory fixes or software updates. Search by VIN on the manufacturer site or nhtsa.gov.
Inspect wiring and connectors Visually inspect the wiring harness and connectors related to the engine cooling and temperature control for damage, corrosion, chafing or poor contact.
Subsystem check Check for supply voltage at the engine coolant temperature (ECT) sensor circuit intermittent low voltage/iat - b connector first; then measure resistance from the signal wire to ground — near-zero ohms confirms a short to ground in the harness.
Subsystem check Watch coolant temperature in live data during warmup — it should climb smoothly to operating temperature.
Subsystem check Check coolant level and feel upper/lower radiator hoses to verify thermostat operation.
Verify the repair Clear the code, complete a full drive cycle including the conditions from the freeze frame, and confirm P1119 does not return.

Approximate repair cost

Repair cost depends on which component actually failed. Typical scenarios for P1119 (parts and labor, USD, independent shop rates): Cooling system repair (pump, fan, radiator): $300–$1,200; Replace the coolant temperature sensor: $100–$300; Replace the thermostat: $150–$400. Overall, fixing P1119 usually costs between $100 and $1,200. An accurate diagnosis before buying parts saves money — the most expensive scenario is rarely the first one to check.

Common questions

Is it safe to drive with P1119?

Drive with caution and watch the temperature gauge. A thermostat stuck open mainly costs fuel; any sign of overheating means stop immediately — driving an overheating engine destroys head gaskets and worse.

Will P1119 clear itself?

Sometimes P1119 clears after a few drive cycles if the fault was intermittent — for example a loose connector or a tank of bad fuel. The underlying cause usually remains, so the code tends to return. Clear it once; if it comes back, diagnose rather than erase it repeatedly.

What is the most common cause of P1119?

The most common causes are: water pump or radiator issues, low coolant level or air in the system, thermostat stuck open or closed.

What are the symptoms of P1119?

Drivers most often notice: cooling fans running constantly, poor cabin heat, Check Engine Light on, temperature gauge reads low or never reaches normal.

How much does it cost to fix P1119?

Cooling system repair (pump, fan, radiator) — $300–$1,200; Replace the coolant temperature sensor — $100–$300; Replace the thermostat — $150–$400. Exact cost depends on the root cause, your vehicle and local labor rates — a proper diagnosis is the cheapest first step.

The engine relies on continuous temperature feedback to run efficiently. The Engine Coolant Temperature (ECT) sensor acts as the primary source of this information, threading into the engine block or thermostat housing where it behaves like a temperature-controlled resistor. As coolant heats up, the sensor's electrical resistance drops, sending a changing voltage signal back to the powertrain control module. This data governs fuel injection quantity, transmission shift scheduling, cooling fan activation, and cabin climate control. Without accurate readings, the engine runs poorly and emissions rise.

Code P1119 indicates the control module has detected a "circuit low" condition on the ECT sensor's secondary (B) circuit. Specifically, the voltage signal has dropped below the expected minimum threshold and stayed there. The term "intermittent" means the fault comes and goes rather than holding steady. On vehicles equipped with dual temperature sensors—common in hybrid models or those with zoned climate systems—this B-circuit designation separates the secondary sensor from the primary ECT input. When the signal wire shorts to ground, connector pins corrode, or the sensor internally fails shorted, voltage collapses toward zero and the module logs P1119.

The ECU stores this code after confirming the fault across multiple drive cycles, ensuring temporary glitches don't trigger false alarms. Associated freeze frame data captures RPM, engine load, vehicle speed, and coolant temperature at the moment of failure—critical context for reproducing the condition during diagnosis.

Common Symptoms of P1119

Check Engine Light illuminates on the dashboard
Cooling fans run continuously or fail to activate at all
Temperature gauge reads abnormally low or never reaches normal operating range
Cabin heating is weak or slow despite engine running at temperature
Fuel consumption increases due to erroneous rich-running corrections
Overheating warnings appear under heavy load or stop-and-go traffic
Erratic gauge behavior or fluctuating readings during warm-up

What Causes P1119?

Failed or internally shorted ECT sensor pulling the signal to ground
Damaged wiring harness with chafed insulation causing a short to the chassis
Corroded or loose terminals in the sensor electrical connector
Low coolant level or air trapped in the cooling system creating false readings
Thermostat stuck in the open position allowing insufficient warm-up
Faulty cooling fan motor or fan relay causing secondary electrical faults
Water pump or radiator issues indirectly affecting sensor readings

How to Diagnose P1119

Connect an OBD2 scanner and confirm P1119 is stored. Record all freeze frame data—this shows engine conditions exactly when the fault occurred and guides your road test.
Scan for any other stored trouble codes. Related codes often point to the root cause, such as short circuits in other sensors sharing the same power supply.
Perform a thorough visual inspection of the ECT sensor wiring and connector. Look for melted insulation near heat sources, broken wires at connector pins, and white or green corrosion buildup blocking electrical contact.
Measure voltage at the sensor connector with the key on engine off. A functioning circuit shows approximately 5 volts reference at the signal terminal. Then check resistance across the sensor itself—the value should decrease predictably as you heat the sensor with a heat gun.
Inspect coolant level in the overflow tank and radiator. Air pockets cause unpredictable temperature readings that can trigger intermittent codes.
Operate the vehicle and monitor live ECT data on the scanner. The reading should climb smoothly during warm-up and stabilize within normal operating range. Intermittent drops in voltage during the drive cycle confirm the circuit fault.
Clear P1119 after repairs and complete a full drive cycle matching the freeze frame conditions. The code must stay cleared to confirm a successful repair.

Repair Options and Costs

Sensor replacement is the most straightforward fix. A new ECT sensor costs $30–$100 for parts alone, with labor adding $70–$200 depending on accessibility. Total cost: $100–$300.

Thermostat issues requiring replacement run $150–$400 total. The part itself is relatively inexpensive ($20–$80), but labor can be significant since the thermostat often sits behind other components.

Cooling system repairs involving the water pump, radiator, or cooling fan motor range from $300–$1,200. These are larger jobs involving coolant flush, component teardown, and potentially radiator fan relay replacement.

Wiring repairs for chafed harnesses or corroded connectors typically cost $75–$200 if performed as standalone repairs.

Total Repair Cost Summary

Most P1119 diagnoses resolve with the least expensive options. Plan for:

ECT sensor replacement: $100–$300
Thermostat replacement: $150–$400
Cooling fan or water pump repair: $300–$1,200
Wiring harness repair: $75–$200

A proper diagnosis before buying parts prevents unnecessary expense. The sensor fails far more often than the water pump, so check the inexpensive components first.

Can You Drive with P1119?

Caution applies here. The engine will operate with degraded temperature data, but you lose accurate overheating protection. Watch the temperature gauge closely during summer heat or heavy traffic. Any needle movement into the red zone means stop immediately—continued driving risks blown head gaskets, warped cylinder heads, or complete engine seizure. P1119 is not an emergency if the gauge stays normal, but do not ignore the underlying cooling system concern.