P2D21Turbocharger Interstage Pressure Sensor A Circuit
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Can trigger limp mode
- How the car detects it
- Engines with two turbochargers in series can measure the pressure between the low-pressure and the high-pressure compressor. GM's patent on two-stage boost control uses this mid-stage value to split the pressure ratio between both stages and to steer the low-pressure wastegate; Cummins describes the same sensor between the stages and the intercooler. P2D21 is the general circuit code: the module rejects the signal but does not assign it to the low, high or erratic codes. No manufacturer documents P2D21 publicly. California requires input sensors to be checked for circuit faults and boost systems for under- and overboost. Single-turbo engines never set it. Expect reduced boost and power.
- What you may notice
- Check engine light
- Reduced power, boost held to a safe value
- Sluggish response while accelerating
- Likely causes
- LikelyLoose, corroded or oil-soaked sensor connector
- PossibleChafed or heat-damaged harness near the turbochargers
- PossibleFailed interstage pressure sensor
- RareShared 5 V sensor supply faulty
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Medium · Usually a job for a workshop.Typical cost: €100 – €600
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.