C0238

C0238 is a circuit-failure code for the hydraulic modulator pump motor inside the ABS hydraulic control unit (HCU) — the EBCM is commanding the pump motor on (to recharge the accumulator during an ABS event or as part of brake-system self-test) and either not seeing the motor draw current, seeing excessive current, or seeing the motor fail to spin up to commanded speed. The HCU pump is a brushed DC motor that draws 30-100A momentarily on startup and 10-25A during sustained operation; it lives integrated into the HCU casting on most modern systems, which means a failed pump usually means a full HCU replacement rather than a discrete motor swap. Cheapest-first ladder: (1) Scan-tool-actuate the ABS pump motor manually and listen — a healthy pump produces a brief, smooth whirring noise for 1-3 seconds; silence means no motor function (open circuit, failed driver, dead motor brushes); a grinding or labored noise means worn brushes or seized bearings. (2) Current-clamp the pump motor power lead during the scan-tool actuation — expect a 30-100A momentary inrush spike followed by a 10-25A running current. Zero current draw is a circuit-side fault; a high stalled current is a mechanically seized pump. (3) Check the pump motor relay (separate from the valve relay on most systems) — ohm the coil, swap with a known-good identical relay, and re-test. (4) Inspect the motor power feed at the HCU connector for corrosion and the chassis ground point for the EBCM at the body bolt where it's typically mounted. Expensive-misdiagnosis caveat: on Ford F250/F350 SuperDuty with the Hydra-Max hydraulic brake-boost system, C0238 with a 'brake assist failure' message is most often the hydraulic-boost pump (a separate, much higher-displacement pump than a normal ABS pump) failing rather than the ABS modulator pump — the two faults look similar in code form but the parts cost diverges by an order of magnitude ($350 ABS pump vs. $1,800-$2,500 Hydra-Max pump assembly).

Vehicle-specific patterns: 1999-2007 Ford F-250/F-350 SuperDuty with Hydra-Max hydraulic brake boost throws C0238 from the well-documented Hydra-Max pump failure — the symptom escalates from intermittent 'brake assist' messages to a hard pedal and red brake warning light; replacement of the pump-and-reservoir assembly is the durable fix. 2001-2010 GM Silverado HD/Sierra HD with the Duramax diesel and the GM exhaust-brake-integrated ABS module throws C0238 from corroded pump-motor terminals at the HCU where road salt collects in the wheel-well-mounted module. 2003-2008 Dodge Ram 2500/3500 with rear-anti-lock-only systems throws C0238 from a failed RWAL pump motor that's part of an integrated HCU/motor pack. 2005-2012 Mercedes-Benz E-class/S-class with the Sensotronic SBC system throw C0238 from a failed SBC hydraulic unit — Mercedes recalled and capped service costs on many affected VINs, so VIN-coverage check is the first step. Estimated repair: $300 to $2,500.