Powertrain, generic (extended)

P2398 Diesel Intake Air Flow B Position Sensor Circuit Low

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modePossible

P2398 is logged when the position signal of the B intake throttle falls below its lower limit. Likely reasons are a signal lead shorted to ground, a lost 5 V supply, or a broken signal wire that the module input pulls low; on SENT sensors the transmitted raw value can also leave its range. No manufacturer documents P2398 itself. For the A valve, GM's LML reacts to less than 0.40 V persisting 5 s, its SENT-equipped 2017 diesels to under 1 % of 5 V in 200 of 250 checks (two trips), while Ford's 2023 diesels flag readings under 0.08 V lasting 3 s. If several 5 V sensors fail at once, suspect a shorted shared reference circuit. The flap is normally switched off, leaving the EGR loop with less control.

Likely causes

Signal wire shorted to ground
Open 5 V reference or open signal wire
Shared 5 V reference pulled down by another faulty sensor
Internally failed position sensor

Symptoms

  • MIL on
  • Further 5 V sensor codes at the same time
  • Regeneration suspended

Repair estimate

DifficultyMediumDIY possible
Parts and labour€30–500
Time0.5–2 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

diesel intake throttle position sensordiesel intake throttle valvesensor wiring

Related codes

P2399P2396P2397P239AP02E8

References: law.cornell.edu, gsi.ext.gm.com, gsi.ext.gm.com, fordservicecontent.com.