Powertrain, generic (extended)

P284B Shift Fork C Stuck

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modePossible

P284B reports a third fork that refuses to travel. Two situations matter: stuck in neutral, which merely costs the gears of fork C, and stuck in an engaged gear, which is more serious because that shaft then turns with a fixed ratio and a second gear on the same shaft must never be selected. No published OBD strategy assigns P284B, so the code rests on what CARB 13 CCR 1968.2 demands for transmission parts. A hydraulic counterpart can be seen in GM's Corvette table, where stuck-on and stuck-off failures of the selector pilot valve, which steers oil to the rods, set P282A and P2829. Before replacing parts, check fluid level and condition and any valve or actuator codes, since a fork rarely jams without a reason upstream.

Likely causes

Selector or pilot valve not routing pressure to the fork C rod
Low or degraded transmission fluid
Fork C or its rod mechanically jammed

Symptoms

  • Car stays in one gear on one shaft or skips the fork C gears
  • Transmission warning lamp

Repair estimate

DifficultyShop_onlyWorkshop job
Parts and labour€300–4,500
Time2–12 h

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

Parts involved

shift fork cshift fork actuator csynchroniser assembly

Related codes

P2849P284AP284CP282AP2829

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