A 2016 Ford Transit Custom rolled in with a complaint that it loses power at 90 km/h, bringing a cluster of P126 codes with it. The technician noted the specific symptom and pulled codes P02ED, P126A, P126B, P126C, and P126D. When multiple injector circuit faults trigger simultaneously, picking the right diagnostic path prevents throwing expensive parts at a van that only acts up on the highway.
Our diagnostic platform analysed this combination and ranked the most probable failures. Here is how we break down a heavy load fault on this engine.
Thermal degradation of Continental injectors
The most likely culprit, ranked at 75 percent, is electrical degradation of the Continental injectors on cylinders 1 and 4. The 2.0 EcoBlue (YMFS) engine uses a fuel system that is prone to thermal and electrical breakdown of internal insulation.
At idle or when cold, the injector operates normally. The problem surfaces during sustained highway driving and high engine load. When accelerating from 90 km/h, rail pressure exceeds 1400 to 1800 bar. This creates a micro-breakdown or current leak in the input circuit, which the engine control unit flags as a loss of control, setting P126A for cylinder 1 and P126D for cylinder 4.
To prove this, test the insulation resistance of the injector piezo element to ground using a megohmmeter on a hot engine. You can also swap injectors 1 and 4 to different cylinders and test drive under load to see if the codes follow the components.
Physical stress on the wiring harness
The next highest probability is a harness issue, ranked at 65 percent. The injector wiring on this engine routes directly over the valve cover, sitting close to metal brackets, high pressure lines, and the engine lifting eye.
When the van demands high torque at highway speeds, the engine shifts hard on its mounts. This movement pulls the harness and vibrates the wires. If the protective loom is rubbed through, or if the terminal pins for injectors 1 and 4 are loose, the circuit suffers a brief short to ground or an open connection.
Inspect the harness carefully where it passes brackets and fuel pipes. Perform a drag test on the pins in the connectors for the affected cylinders to ensure tight contact.
Module and sensor edge cases
We also have to consider the Continental SID211 engine control unit itself. Ranked at 45 percent, an internal failure of the output stage can cause these exact codes. The ECU groups the output drivers, sharing power circuits or capacitor banks between cylinders 1 and 4. Sustained highway driving pushes the ECU to peak thermal limits, exposing failing MOSFETs or micro-cracks in the solder. A 21-watt bulb load test on the wiring from the PCM to the injectors helps rule this out.
Finally, a calibration shift in the exhaust gas temperature sensors sits at a 35 percent probability. If an EGT sensor sticks at a falsely low reading, the PCM attempts to heat up the system for regeneration. It drastically increases the injection pulse duration and energy. At 90 km/h, this overloads the injector supply circuits and pushes the current outside allowable limits. Check the EGT sensor readings on a cold engine against ambient temperature, then monitor them in live data under load.
Next steps for the bay
Intermittent highway faults require testing components at their physical and thermal limits. Let me know if you see this pattern on the 2.0 EcoBlue engines in your shop, or map your next set of intermittent codes through our platform to get these exact testing steps.