A P0408 code on your 2023 Chevrolet Equinox indicates high voltage detected in the EGR position sensor B circuit. Like its low-circuit counterpart, this code points to a specific sensor within a multi-sensor EGR system.
High Circuit Interpretation
High voltage in a sensor circuit typically indicates an open condition—the signal wire is broken or the sensor has failed open internally. Without the sensor's normal resistance in the circuit, the ECM sees the full reference voltage, registering as an abnormally high reading.
Equinox Engine Details
The 2023 Equinox offers the 1.5L turbocharged four-cylinder engine. GM's modern EGR systems may use dual position sensors for verification and accuracy. The sensor B circuit operates independently from sensor A, allowing isolated fault identification.
Diagnostic Approach
Use GM GDS2 to compare sensor A and B readings. If sensor A reads correctly while B is stuck high, the problem is isolated to the B circuit. Check for open circuits in sensor B wiring. Test the sensor B connector for proper pin contact. Verify the sensor isn't physically disconnected.
Repair Options
Locate and repair any open circuits in the sensor B wiring. If the sensor has failed internally, EGR valve replacement is typically required as sensors are often integrated. Given the 2023 model year, warranty coverage should apply. After repair, verify both sensors track correctly.