All codes
P0408Emissions System
Exhaust Gas Recirculation Sensor B Circuit High
P0408 means the EGR position sensor B signal is above the expected electrical range. Learn what to check before replacing parts.
What you may notice
Symptoms
- 01Warning light may illuminate
- 02Intermittent or implausible scan data
- 03Vehicle-specific symptoms may vary
Where to look first
Common causes
- 01An open ground, short to voltage, connector damage, or sensor fault can produce a high signal.
- 02Wiring, connector, or ground fault
- 03Vehicle-specific mechanical or control issue
A sensible sequence
Best diagnostic order
- 01Save codes and freeze-frame information
- 02Inspect the correct EGR valve and position-sensor circuit, then compare the commanded position with feedback using vehicle-specific data.
- 03Confirm readings with vehicle-specific specifications
- 04Verify the repair under the conditions that set the code
Step by step
What to check and repair
- 01Inspect the correct EGR valve and position-sensor circuit, then compare the commanded position with feedback using vehicle-specific data.
- 02Repair only the verified cause and retest
Read the signals
Live-data clues
Related sensor or switch signal
- Typical behavior
- Plausible and consistent with the operating condition
- Possible clue
- An unexpected value or dropout helps localize the fault
| Parameter | Typical behavior | What it can suggest |
|---|---|---|
| Related sensor or switch signal | Plausible and consistent with the operating condition | An unexpected value or dropout helps localize the fault |
What P0408 means
The EGR position sensor B signal is above the expected electrical range. The code identifies an observed condition; it does not prove which part needs replacement.
Diagnostic direction
Inspect the correct EGR valve and position-sensor circuit, then compare the commanded position with feedback using vehicle-specific data.
Before clearing the code
Save stored and pending codes and freeze-frame data. Use service information for the exact vehicle before repair, then confirm the issue no longer returns.