Powertrain, generic · Ignition system or misfire

P0391 Camshaft Position Sensor B Circuit Range/Performance Bank 2

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modePossible

Camshaft position sensor B is the exhaust camshaft sensor; bank 2 is the side without cylinder 1, so the code only occurs on V and boxer engines with one exhaust cam sensor per bank. P0391 means the bank 2 exhaust cam signal is present, but the number or position of its pulses does not fit the crankshaft. GM's 3.0 twin-turbo V6 (LGW) expects 4 to 6 pulses in the first 12 reference events and 398 to 402 per 100 engine cycles on the four-tooth wheel, after two trips; the Saab 9-4X 2.8 turbo V6 (LAU) checks pulses per crank revolution below 2,520 rpm. The 2004 Northstar requires each edge within a window of crank teeth, and GM's 2004 3.6-litre V6 (LY7) counts implausible signals over two drive cycles. The phaser then goes to its base position and the engine cranks longer. Mechanical causes – damaged tone wheel, jumped chain – matter more here than with P0390.

Likely causes

Tone wheel on the bank 2 exhaust phaser damaged, loose or wrongly fitted
Interference or loose contact producing extra edges
Sensor loose, wrong O-ring or gap, chips on the magnet
Timing chain stretched or jumped
Sensor faulty

Symptoms

  • Check engine light on
  • Loss of power (bank 2 exhaust cam timing in its base position)
  • Longer cranking
  • Rough idle
  • Occasional stalling

Repair estimate

DifficultyMediumDIY possible
Parts and labour€60–1,200
Time0.5–8 h

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

Parts involved

camshaft position sensor exhaustcamshaft tone wheelsensor wiringengine control modulecam phaser exhaust bank2timing chain

Related codes

P0390P0392P0393P0394P0366P0018

References: gsi.ext.gm.com, saabwisonline.com, saabwisonline.com, gsi.ext.gm.com.