P128A on 2018-2020 Ford F-150 — Cylinder Head Temperature (CHT) Sensor Circuit Intermittent/Erratic
1 vehicles · 1 makes · $50-$15,000 repair
Most Reported On
P128A is an OBD-II diagnostic trouble code meaning “Cylinder Head Temperature (CHT) Sensor Circuit Intermittent/Erratic.” A Ford-family powertrain code. The PCM saw the cylinder head temperature sensor signal drop out or jump around erratically while the engine was running, rather than changing smoothly with engine temperature. The CHT sensor threads into the cylinder head itself (not a coolant passage) and Ford uses it for fuel trim, spark timing, cooling fan control and fail-safe cooling, so a bad signal can cause rough running, poor fuel economy, changed fan behavior, or a false overheat/fail-safe event in which the PCM starts disabling injectors. P128A sits in the manufacturer-specific P1xxx block, so confirm the definition against your make before parts are replaced. This code is most commonly reported on 2018-2020 Ford F-150, with repair costs ranging from $50 to $15,000.
Common Causes
Typical Repair Cost
Based on 1 documented vehicle-specific issues. Actual cost depends on root cause and vehicle.
Diagnostic Tools
P128A does not use the standard P/B/C/U prefix. It may be a manufacturer-specific code, so verify that a scanner supports your exact year, model and module before buying.
FAQ
What does P128A mean?
P128A stands for "Cylinder Head Temperature (CHT) Sensor Circuit Intermittent/Erratic." A Ford-family powertrain code. The PCM saw the cylinder head temperature sensor signal drop out or jump around erratically while the engine was running, rather than changing smoothly with engine temperature. The CHT sensor threads into the cylinder head itself (not a coolant passage) and Ford uses it for fuel trim, spark timing, cooling fan control and fail-safe cooling, so a bad signal can cause rough running, poor fuel economy, changed fan behavior, or a false overheat/fail-safe event in which the PCM starts disabling injectors. P128A sits in the manufacturer-specific P1xxx block, so confirm the definition against your make before parts are replaced.
What are the most common causes of P128A?
The most common causes of P128A are: Failing cylinder head temperature sensor (intermittent internal fault), Corroded, loose, or backed-out CHT sensor connector terminals, Chafed or broken CHT signal/ground wiring in the harness, Poor engine ground or shared sensor ground fault, Actual cooling system problem (low coolant, stuck thermostat) causing erratic readings, PCM fault (rare, diagnose wiring and sensor first). The specific cause varies by vehicle.
How much does it cost to fix P128A?
Repair costs for P128A range from $50 to $15,000, depending on the vehicle and root cause.
Which vehicles are affected by P128A?
Au7o has documented P128A across 1 vehicle models from 1 manufacturers: Ford.
Content compiled with AI assistance using NHTSA complaints, TSBs, and owner reports. May contain errors. Always verify with your vehicle's service manual.