Code
C2120
HYUNDAI
C — Chassis
Servo Pump Relay
Views:
UK: 11
EN: 21
RU: 13
AI status
Completed
Completed
100%
Causes
- Blown fuse for pump/relay circuit
- Faulty pump relay (stuck open or shorted)
- Open, shorted or corroded wiring/connectors between relay, pump and control module
- Poor ground at pump, relay or control module
- Failed pump motor (high current draw or open)
- Faulty ABS/ESC control module or relay drive transistor
Symptoms
- ABS, ESC or VDC warning lamp illuminated
- Brake/ABS pump not running when system requests it
- Unusual noise or no noise from pump during self-test
- Intermittent operation of ABS/VDC functions
- Possible longer brake pedal recovery after ABS event
What to check
- Read and record freeze frame and related DTCs with a scan tool
- Check ABS/ESC warning lamps and perform system self-test
- Visually inspect fuses, pump relay and wiring harness for corrosion or damage
- Check connector pins for corrosion, looseness or pushed-out terminals at relay, pump and control module
- Measure battery voltage and ground quality at relay and pump
- Perform relay bench test or swap with known-good relay of same type
Signal parameters
- Ignition ON: supply voltage to relay feed ≈ battery voltage (12–14.5 V)
- Relay coil control: driver output should be ~0 V (low) when off and battery voltage when energized (or converse depending on vehicle wiring); verify with OEM wiring diagram
- Relay coil resistance (typical automotive 12 V relay): ~50–200 Ω (refer to specific relay spec)
- Pump motor DC resistance: low ohms (typically
- Pump motor current draw: can be several amps when operating; excessive current (> manufacturer spec) suggests seizure/short
Diagnostic algorithm
- Use a scan tool to confirm C2120, note related codes (ABS/ESC), clear codes and re-run self-test to reproduce.
- Visually inspect pump relay, fuse(s) for pump circuit and associated wiring/connectors for damage or corrosion.
- With key OFF, disconnect relay and inspect socket terminals. Check for heat damage or loose pins.
- With key ON, measure voltage at relay feed terminal — should be battery voltage. If no voltage, trace upstream fuse/wiring.
- Command pump ON with scan tool (if available) while monitoring relay coil control pin voltage and feed voltage. If feed present but coil not driven, suspect control module output.
- If coil is driven but relay does not click, bench-test or swap relay with known-good unit. Replace relay if faulty.
- If relay clicks but pump does not run, measure voltage at pump connector while commanded. If voltage present but pump does not run, test pump motor resistance and current; replace pump if defective.
- If no voltage at pump and relay is good, trace wiring between relay and pump for an open/short and repair.
- Check/repair grounds for pump and control module. Reassemble, clear codes and road-test to confirm repair.
- If wiring, relay and pump check good and control module still fails to drive relay, consult OEM module testing procedures or replace module as last resort.
Likely causes
- Failed pump relay
- Loose/corroded connector at relay or pump
- Blown fuse or poor ground
- Pump motor failure (seized or shorted)
- Control module output fault
Fault status
Status
Fault in servo pump relay circuit — power or control to the brake/servo pump is missing or abnormal. ABS/ESC assist pump may not run when required.
Repair difficulty: Medium
Diagnostic time: 0.5-2.0 hours
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