Code
C0021
LAND ROVER
C — Chassis
Performance of brake accelerator
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UK: 15
EN: 127
RU: 21
AI status
Completed
Completed
100%
Causes
- Faulty accelerator pedal position sensor (APP) or sensors
- Faulty brake pedal switch or brake pressure sensor
- Damaged wiring, corroded connector, or poor ground in pedal circuits
- CAN bus or module communication error (ABS, engine ECU, BCM)
- Intermittent battery/charging system voltage or power supply faults
- Software or calibration mismatch in one or more control modules
Symptoms
- Malfunction Indicator Lamp (MIL) or ABS/ESC warning lamp illuminated
- Reduced engine power or 'limp' mode activated
- Cruise control disabled or unavailable
- Inconsistent or unexpected pedal response (hesitation, delayed throttle)
- Brake-related warnings or traction control/ABS interventions without driver input
- Fault(s) may be intermittent or occur after vibration/temperature changes
What to check
- Read and record all stored DTCs and freeze-frame data from engine, ABS, BCM and other relevant modules
- Check battery voltage with key on/engine off — should be within manufacturer spec (generally ~12.4–12.8 V at rest)
- Inspect connectors and wiring at accelerator pedal module, brake pedal switch and ABS/ECU for corrosion, damage or loose pins
- Check for CAN-bus related codes (U0xxx series) and physical damage to CAN wiring
- Scan live data: APP sensor channels A and B, brake switch state, brake pressure sensor and ABS wheel speed data
- Perform wiggle tests on harness while monitoring live data for intermittent changes
Signal parameters
- Accelerator pedal position sensor: dual channel outputs typically vary across ~0.5–4.5 V as pedal moves (two independent ramp signals should track each other)
- Brake light switch: two-state signal (usually ~0 V vs battery voltage depending on switch design) — confirm OEM spec
- Brake pressure sensor (if fitted): output varies with pressure, see manufacturer ranges
- CAN bus nominal idle voltages: CAN_H and CAN_L common-mode around ~2.5 V; differential signaling with expected message rates for modules (verify bus activity with a scope/scan tool)
- Module supply: stable 12 V (key on) and solid ground connection; reference 5 V sensor supply present where applicable
Diagnostic algorithm
- Retrieve all DTCs and freeze-frame data from engine, ABS, transmission and chassis modules. Note event conditions (speed, throttle, brake status).
- Visually inspect pedal assemblies, connectors and harnesses for damage, contamination, pin corrosion, or loose connections. Repair any visible faults.
- Verify battery and charging system health; ensure stable vehicle voltage during testing. Recharge if low and recheck code.
- With a scan tool, observe live data for accelerator channels A/B, brake switch state and brake pressure (if present). Compare both APP channels for matching response across full pedal travel.
- Perform a wiring wiggle test while monitoring live data to expose intermittent faults. Inspect ground and power pins for resistance to body/chassis.
- If CAN-bus or inter-module communication errors are present, inspect CAN wiring, terminators and check for module faults. Use an oscilloscope to verify CAN signals and message integrity.
- If a sensor channel is out of expected voltage range or channels disagree, measure sensor signal, reference and ground with a DMM/oscilloscope. Replace sensor and re-test if out of spec.
- If modules show corrupted or unexpected behavior and wiring is good, check for software updates or perform module reprogramming/initialization per manufacturer procedures.
- Clear codes and road-test under similar conditions to attempt re-creation. If code returns, follow guided replacement of the most likely failed component based on measured faults.
- After repair, clear all codes and confirm no recurrence; verify related systems (cruise, ABS, traction) operate normally.
Likely causes
- Faulty accelerator pedal position sensor(s) (common failure)
- Faulty brake pedal switch or connector
- Intermittent/poor ground or power to pedal sensors or receiving module
- CAN bus message loss or corruption between ABS/ECU/BCM
Fault status
Status
Stored when brake and/or accelerator input signals or their communication are outside expected parameters or inconsistent between redundant channels/modules. Can be intermittent or permanent depending on wiring, sensor or communication failures.
Repair difficulty: Medium
Diagnostic time: 0.5-2.5 hours
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