Powertrain, generic · Transmission

P0978 Shift Solenoid C Control Circuit Range/Performance

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modePossible

Range/performance fault in the drive circuit of shift solenoid C. GM's 2007 Allison 1000 table used it for an open SS3 circuit, but only while the commanded gear is not reverse trim, 5th or 6th; the table even prints the label Circuit Low beside an open-circuit test, an apparent typo. FCA lists P0978 among the four codes that the 2014–2016 9-speed transaxle set under old software when the range sensor harness had poor crimps. Ferrari's DCT bulletin uses it for a missing signal from the actuator 4 engage position sensor. Ford and GM six-speeds do not use it. Low/high are P0979/P0980, the current open code P097C.

Likely causes

Intermittent high resistance at crimped harness terminals (FCA 9-speed)
Open coil of shift solenoid C (Allison-type usage)
Transmission software that predates the manufacturer's fix
Faulty driver stage in the transmission control module

Symptoms

  • MIL or transmission warning on
  • Sudden neutral or default gear while driving
  • Erratic or missing shifts

Repair estimate

DifficultyHardWorkshop job
Parts and labour€0–1,500
Time0.5–5 h

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

Parts involved

shift solenoid cwiring harnesstcm

Related codes

P097CP0979P0980P0760P0975P0981

References: gsi.ext.gm.com, static.nhtsa.gov, static.nhtsa.gov.