P0977 code meaning
Shift Solenoid B Control Circuit High
Powertrain system Generic code P09xx codes Check engine light
What P0977 means
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.
P0977 at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modePossible
- Repair difficultyHard
- Typical labor1 to 5 hours
- Clears after repairWhen cleared with a scanner
Symptoms of P0977
- Limp mode with only reverse and one high forward gear
- Weak acceleration from rest
- MIL or transmission warning, depending on calibration
Common causes of P0977
- Most 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
- Less likelyFaulty driver stage in the control module
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Shift solenoid bWiring harnessTCM
What each part of P0977 means
| P | Powertrain system: engine, fuel system, ignition, emissions and transmission. |
| 0 | Generic code: it means the same on every make (SAE standard). |
| 9 | Area: transmission. |
| 77 | The exact fault in that area. |
What to do next
- Note P0977 and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about P0977
What does P0977 mean?
P0977 means "Shift Solenoid B Control Circuit High". High-voltage fault in the control circuit of shift solenoid B. It is a generic code, so it means the same on every make.
Is it safe to drive with P0977?
Drive gently and only to a workshop. With P0977 the car can go into limp mode (reduced power) to protect itself.
Will P0977 fail an emissions test?
Yes, it can. P0977 is emissions-related, so most inspection programs fail a car while it is stored or while the check engine light is on.
How hard is P0977 to fix?
Difficulty: hard. A typical repair takes 1 to 5 hours of work. This is a job for a workshop.
Will P0977 clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.