P0977Shift Solenoid B Control Circuit High
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Can trigger limp mode
- How the car detects it
- High-voltage fault in the control circuit of shift solenoid B. GM six-speeds put an open or a power short of the mode 3 multiplex valve here, 1.2 of 1.5 s; the 2016 table sets it without MIL, the 2019 table with MIL after one trip. The Saab 9-4X 6T70 treats it more severely than P0976: 2 s, Type A, high-side driver off, only reverse and 5th gear left, no converter lockup. Ford uses it strictly for SSB short to power, as in its 2012 and later summaries. GM's Allison 1000 checks for 0.39 ohm or less to a supply over three samples (75 ms in 2016, 60 ms in 2023). FCA 9-speed and Aisin uses are not documented for this code. Ground-side faults are P0976.
- What you may notice
- Limp mode with only reverse and one high forward gear
- Weak acceleration from rest
- MIL or transmission warning, depending on calibration
- Likely causes
- LikelyOpen solenoid B coil or wire on GM six-speeds, where opens report as high
- PossibleControl wire shorted to battery or a switched supply
- PossibleDamaged pins or seals at the transmission pass-through connector
- RareFaulty driver stage in the control module
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Hard · Usually a job for a workshop.Typical cost: €100 – €1,600
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.