P128A on 2018-2020 Ford F-150 — Cylinder Head Temperature (CHT) Sensor Circuit Intermittent/Erratic
1 vehicles · 1 makes · $50-$15,000 repair
How to diagnose and fix P128A: most-reported vehicles
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Ford F-150 · 2018–2020
The 2018-2020 F-150 3.0L Power Stroke diesel uses a Bosch CP4.2 high-pressure fuel pump. The CP4 was engineered for high-lubricity European diesel, not U.S. ultra-low-sulfur diesel, so its internal roller/cam followers can run dry and gall. Air ingress and cavitation accelerate the wear. When the pump fails it doesn't just stop — it 'grenades,' sending metal shavings throughout the entire high-pressure fuel system, destroying injectors, rails, lines, and the tank in a cascade. Owners have reported failures as early as ~48,000 miles, and the resulting whole-system replacement commonly runs $8,000-$15,000+. It is the single most catastrophic issue for the F-150 diesel.
Common Symptoms
- Sudden loss of power / engine stall and no-restart
- Hard starting or extended cranking
- Metal debris found in fuel filter
- Fuel-system / powertrain warning lights
- Rough running before total failure
How to Fix
Prevention is key: run a quality diesel fuel/lubricity additive at every fill, change the fuel filters on schedule, prime carefully and avoid running the tank to empty (air ingress), and consider a CP4 'disaster prevention'/bypass kit that routes pump weep fuel and filters debris before it reaches the tank/lines. After a failure, the entire high-pressure side must be replaced — the Bosch CP4 pump, all injectors, rails, lines, and tank flush. Some owners convert to a more tolerant pump. Prevention kit/additive $50-$500; post-failure repair $8,000-$15,000+.
Sources for this issue (2)
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P128A code reference
General diagnostic-code context. The code alone does not confirm a cause for your vehicle; use the applicable issue card and its sources.
Frequently asked questions
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.
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Content compiled with AI assistance using NHTSA complaints, TSBs, and owner reports. May contain errors. Always verify with your vehicle's service manual.