Code
C1401
MERCEDES-BENZ
C — Chassis
High Pressure Return Pump Circuit Open/Shorted; Will Not Shut Off
Views:
UK: 23
EN: 42
RU: 19
AI status
Completed
Completed
100%
Causes
- Open or shorted wiring between pump and control module
- Corroded or loose connector at the pump or module
- Failed high-pressure return pump motor
- Stuck or welded relay/contact that supplies the pump
- Faulty ABS/ESP control module
- Blown or intermittent fuse/power supply fault
Symptoms
- ABS/ESP warning light(s) illuminated on dash
- High-pressure pump audible and runs continuously or more frequently than normal
- Battery drain when vehicle is parked
- Reduced or altered ABS/ESP functionality
- Possible brake pedal feel changes during ABS events
What to check
- Read and record all stored DTCs and freeze-frame data with a Mercedes-capable scan tool
- Visually inspect pump connector and wiring harness for corrosion, damage, or water ingress
- Check related fuses and relays for proper operation
- Backprobe pump power and ground while commanding pump on/off with scanner
- Measure voltage at pump power terminal (engine off and running) and observe changes when commanded
- Perform resistance and continuity checks from pump connector to ABS/ESP module pins
Signal parameters
- Battery supply voltage to pump: typically ~11–14 V (varies with battery/charging)
- Control signal: switched ground or module-driven transistor/PWM (duty 0–100%)
- Pump current draw (typical running range): expect single-digit amps; a very high or zero reading indicates fault
- Connector resistance to module: near 0 ohms for power/ground; open circuit indicates break
- No high-voltage signals—vehicle electrical system remains low-voltage 12 V domain
Diagnostic algorithm
- Retrieve and note all faults; clear codes and attempt to reproduce. If code returns, continue.
- Listen for pump operation and verify if it runs continuously. Note conditions when it runs (ignition on, engine off, during ABS events).
- Visually inspect pump connector and harness for corrosion, bent pins, water, or damage. Repair any evident damage.
- Check fuses and relays in the pump/power supply circuit. Replace suspect items and re-test.
- Backprobe the pump connector: verify constant battery supply and check the control return/ground while commanding pump on/off with a scan tool. Observe voltage changes.
- Measure continuity between pump power/ground pins and ABS/ESP module pins to locate opens or shorts. Repair wiring as needed.
- Measure pump current while operating. High current suggests mechanical/electrical motor failure; zero or no change suggests no power or open circuit.
- If wiring, fuses and relays check good and pump is receiving correct control but still behaves incorrectly, replace the pump assembly.
- If pump and wiring are good but control signal is abnormal, consider ABS/ESP control module diagnostics or replacement (confirm with module bench testing or dealer-level procedures).
- After repairs, clear codes and perform a road/operational test and re-scan to confirm the fault is resolved.
Likely causes
- Damaged connector or corroded pins at the pump
- Broken/shorted harness (chafing, water ingress)
- Pump motor internal failure (runs continuously or stuck on)
- Relay or power transistor in module stuck closed
- Module reporting or interpreting incorrect signal due to internal fault
Fault status
Status
High Pressure Return Pump Circuit Open/Shorted — pump will not shut off; ABS/ESP systems affected.
Repair difficulty: Medium
Diagnostic time: 1.0-3.0 hours
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