P277B: Electric/Auxiliary Transmission Fluid Pump B Driver Circuit Performance

P277B concerns the power stage that energises the motor of auxiliary pump B, wherever it sits: inside a separate pump controller or in the transmission module. The stage is switched on, but what comes back – current, speed or a status signal – does not fit the command, so the module rates the driver as implausible rather than reporting a plain open or short. No manufacturer documents P277B publicly. For pump A, Ford's 2024 OBD summary (10R60/10R80, 8F57) lists a related case: the pump flags implausible current together with implausible speed, stored as P0C29 (UDS P0C29_92). Overheated or failing driver electronics, a poor ground, low system voltage and a pump that loads the stage abnormally are the usual triggers. The gearbox then runs without the pump's support, which mainly affects stop-start.

Symptoms

• Transmission warning or service message
• Stop-start unavailable
• Jerky drive-off after engine restarts

Most likely causes

• Failing output stage in the pump controller or TCM
• Poor ground or low system voltage at the driver
• Pump motor loading the driver abnormally
• Loose or corroded pins between driver and pump

What to check, in order

Start with the simplest. You can tick off each step.

1. Check the fluid level and condition
2. Compare the reading with other engine data while varying the engine speed.
3. Read the input and output speed in live data
4. Check the connector and wiring
5. Check for other related engine codes
6. Consult the manufacturer's procedure for the transmission

Good to know

• Repair difficulty: hard
• It can trigger limp mode.

What each character of P277B means

• P: Powertrain: engine and transmission
• 2: Generic code: same on every make
• 7: Transmission
• 7B: Specific fault in that system

Frequently asked questions

Can I keep driving with code P277B?

Drive gently to a repair shop. If it slips, you hear clunks, or it loses its gears, do not keep driving.

What causes code P277B?

The most common causes are: failing output stage in the pump controller or TCM; poor ground or low system voltage at the driver; pump motor loading the driver abnormally.

Related codes

• P0C29Electric/Auxiliary Transmission Fluid Pump A Driver Circuit Performance
• P277DElectric/Auxiliary Transmission Fluid Pump B Motor Over Temperature
• P276FElectric/Auxiliary Transmission Fluid Pump B Motor Current High
• P276BElectric/Auxiliary Transmission Fluid Pump B Motor Supply Voltage Circuit Low

Sources

• fordservicecontent.com: OBDSM2400OUTPUT 16Jul2024 WSM final V2 MCS7001
• static.nhtsa.gov: MC 10153066 9999
• law.cornell.edu: 13 CCR 1968.2

Values and procedures vary by manufacturer. If it affects brakes, steering, fuel or high voltage, see a professional. Updated: 2026-11-04. How we build these pages.