Code
U040C
Generic
U — Network/User
Invalid Data Received From Exhaust Gas Recirculation Control Module B
AI status
Completed
Completed
100%
Causes
- Faulty EGR Control Module B
- Damaged or corroded wiring/connectors between ECM and EGR Control Module B
- Loss of ground or supply voltage to the EGR control module
- Faulty or intermittent CAN/LIN bus (electrical fault, missing termination, short)
- Software/calibration mismatch or corrupted module firmware
- Intermittent connection (wiring chafe, water intrusion)
Symptoms
- Malfunction Indicator Lamp (MIL) or warning lamp illuminated
- Reduced engine performance, increased emissions, or limp-home mode
- EGR system faults or EGR not operating as commanded
- Multiple network-related DTCs present
- Intermittent drivability issues, rough idle, or hesitation
What to check
- Use a capable scan tool to read U040C and any related DTCs; record freeze frame and occurrence counts
- Verify presence of EGR Control Module B on the network (module ID/listing) and attempt to communicate with it via scanner
- Check for other network fault codes (U0100 series, U0121, etc.) that indicate broader bus issues
- Inspect EGR module connector and harness for corrosion, water intrusion, broken pins, or damaged insulation
- Verify battery voltage and chassis/engine ground(s) are within specification
- Backprobe EGR module power and ground while key on/engine running
Signal parameters
- CAN bus idle voltages ~2.5 V on CAN_H and CAN_L (both roughly mid-supply); dominant state shifts CAN_H higher (~3.5–4.0 V) and CAN_L lower (~1.0–1.5 V) — verify with oscilloscope if available
- Typical CAN data rates: 250 kb/s or 500 kb/s (vehicle specific) — verify messages present at expected data rate
- LIN signals: dominant low (approx 0 V) and recessive pulled high via master; wake/voltage levels vary by system
- Expected behavior: consistent periodic messages from EGR Control Module B when awake; absence or corrupted frames indicate fault
Diagnostic algorithm
- Connect a scan tool and confirm U040C and any related network codes. Record freeze frame data and occurrence history.
- Attempt bi-directional communication with EGR Control Module B. Note if tool reads module parameters or reports no response.
- Inspect physical connectors and wiring at EGR Control Module B and at the PCM/gateway. Repair any damage, corrosion, or loose pins.
- With ignition on, verify module supply voltage and ground at the EGR module connector. Repair any power/ground issues.
- Measure CAN_H and CAN_L voltages at the EGR module and at the PCM/gateway. Compare to expected idle voltages and look for differences between locations.
- Use an oscilloscope to view CAN waveforms. Look for noise, missing frames, erratic levels, or bus collisions. Verify termination resistance (~60 ohms across CAN_H and CAN_L).
- If wiring and bus are good, try updating or reflashing EGR Control Module B and the PCM/gateway software to the latest calibration per manufacturer service information.
- If bench/verifications indicate the module is unresponsive, swap or replace EGR Control Module B with a known-good unit if available (or isolate with manufacturer-approved procedure) and retest.
- Clear codes and perform a road test to confirm the fault does not return. If intermittent, monitor network traffic during reproduction of symptoms.
Likely causes
- Open/short or high resistance in CAN/LIN wiring to EGR Control Module B
- Bad connector or corrosion at the EGR module harness or ground
- EGR Control Module B internal failure or corrupted firmware
- Network termination problem or other module pulling bus lines low/high
Fault status
Status
Control module reports invalid or corrupted data received from the Exhaust Gas Recirculation Control Module B; indicates a communications or module fault on the vehicle data bus.
Repair difficulty: Medium
Diagnostic time: 1.0-3.0 hours
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Code
U040C
HYUNDAI
U — Network/User
Invalid Data Received From Exhaust Gas Recirculation Control Module “B”
AI status
Completed
Completed
100%
Causes
- Faulty EGR Control Module B
- Damaged or corroded wiring/connectors between ECM and EGR Control Module B
- Loss of ground or supply voltage to the EGR control module
- Faulty or intermittent CAN/LIN bus (electrical fault, missing termination, short)
- Software/calibration mismatch or corrupted module firmware
- Intermittent connection (wiring chafe, water intrusion)
Symptoms
- Malfunction Indicator Lamp (MIL) or warning lamp illuminated
- Reduced engine performance, increased emissions, or limp-home mode
- EGR system faults or EGR not operating as commanded
- Multiple network-related DTCs present
- Intermittent drivability issues, rough idle, or hesitation
What to check
- Use a capable scan tool to read U040C and any related DTCs; record freeze frame and occurrence counts
- Verify presence of EGR Control Module B on the network (module ID/listing) and attempt to communicate with it via scanner
- Check for other network fault codes (U0100 series, U0121, etc.) that indicate broader bus issues
- Inspect EGR module connector and harness for corrosion, water intrusion, broken pins, or damaged insulation
- Verify battery voltage and chassis/engine ground(s) are within specification
- Backprobe EGR module power and ground while key on/engine running
Signal parameters
- CAN bus idle voltages ~2.5 V on CAN_H and CAN_L (both roughly mid-supply); dominant state shifts CAN_H higher (~3.5–4.0 V) and CAN_L lower (~1.0–1.5 V) — verify with oscilloscope if available
- Typical CAN data rates: 250 kb/s or 500 kb/s (vehicle specific) — verify messages present at expected data rate
- LIN signals: dominant low (approx 0 V) and recessive pulled high via master; wake/voltage levels vary by system
- Expected behavior: consistent periodic messages from EGR Control Module B when awake; absence or corrupted frames indicate fault
Diagnostic algorithm
- Connect a scan tool and confirm U040C and any related network codes. Record freeze frame data and occurrence history.
- Attempt bi-directional communication with EGR Control Module B. Note if tool reads module parameters or reports no response.
- Inspect physical connectors and wiring at EGR Control Module B and at the PCM/gateway. Repair any damage, corrosion, or loose pins.
- With ignition on, verify module supply voltage and ground at the EGR module connector. Repair any power/ground issues.
- Measure CAN_H and CAN_L voltages at the EGR module and at the PCM/gateway. Compare to expected idle voltages and look for differences between locations.
- Use an oscilloscope to view CAN waveforms. Look for noise, missing frames, erratic levels, or bus collisions. Verify termination resistance (~60 ohms across CAN_H and CAN_L).
- If wiring and bus are good, try updating or reflashing EGR Control Module B and the PCM/gateway software to the latest calibration per manufacturer service information.
- If bench/verifications indicate the module is unresponsive, swap or replace EGR Control Module B with a known-good unit if available (or isolate with manufacturer-approved procedure) and retest.
- Clear codes and perform a road test to confirm the fault does not return. If intermittent, monitor network traffic during reproduction of symptoms.
Likely causes
- Open/short or high resistance in CAN/LIN wiring to EGR Control Module B
- Bad connector or corrosion at the EGR module harness or ground
- EGR Control Module B internal failure or corrupted firmware
- Network termination problem or other module pulling bus lines low/high
Fault status
Status
Control module reports invalid or corrupted data received from the Exhaust Gas Recirculation Control Module B; indicates a communications or module fault on the vehicle data bus.
Repair difficulty: Medium
Diagnostic time: 1.0-3.0 hours
Similar codes
Repair manuals
Manual library for HYUNDAI
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