What does it mean?
This is a generic diagnostic trouble code (DTC) that applies to OBD-II vehicles with an automatic transmission. This may include, but is not limited to, vehicles from Ford, GMC, Chevrolet, Honda, BMW, Saturn, Land Rover, Acura, Nissan, Saturn, etc. Although generic, the exact repair steps may vary depending on the year, make, model, and powertrain configuration.
In most cases, automatic transmissions will incorporate at least three pressure control solenoids known as solenoids A, B, and C. Newer transmissions tend to have more speeds and more solenoids. Various trouble codes are associated with the “B” solenoid control circuit, and some of the most common include P0964, P0965, P0966, and P0967. When the OBD-II trouble code P0966 is set, the Powertrain Control Module (PCM) has detected a problem with the “B” transmission pressure control solenoid control circuit. The specific code set is based on the specific malfunction detected by the PCM.
An automatic transmission is controlled by bands and clutches that change gears by having fluid pressure in the right place at the right time. The purpose of the transmission pressure control solenoids is to regulate the fluid pressure so that the automatic transmission operates correctly and shifts smoothly. The PCM monitors the pressure inside the solenoids and directs fluid to various hydraulic circuits that change the gear ratio precisely as needed.
The P0966 code is set by the PCM when it detects that the “B” pressure control solenoid control circuit is experiencing a low voltage condition and is therefore not functioning properly.
How severe is this DTC?
The severity of this code normally starts as moderate, but it can escalate to a more severe level quickly when not corrected in a timely manner. In circumstances that cause the transmission to slam into gear, permanent internal damage can be caused, making the issue serious.
What are some of the symptoms of the code?
Symptoms of a P0966 trouble code may include:
- Increased fuel consumption
- Check engine light illuminated
- Transmission overheating
- Transmission slipping during gear shifts
- Transmission shifts hard (gear slam)
- Potential missed symptoms
- Transmission put into limp mode by the PCM
What are some common causes of the code?
Causes of this P0966 transmission code may include:
- Faulty pressure control solenoid
- Contaminated transmission fluid
- Restricted transmission filter
- Faulty transmission pump
- Faulty transmission valve body
- Blocked hydraulic passages
- Corroded or damaged connector
- Faulty or damaged wiring
- Faulty PCM
What are the troubleshooting steps for P0966?
Before starting the troubleshooting process for any malfunction, you should research the Technical Service Bulletins (TSBs) for the specific vehicle by year, model, and transmission. In some situations, this can save you a lot of time in the long run by pointing you in the right direction.
Fluid and Wiring Inspections
The first step is to check the fluid level and examine the condition of the fluid for contamination. Before changing the fluid, you should (if possible) check the vehicle’s records to verify the last time the filter and fluid were changed.
A detailed visual inspection to check the condition of the wiring for obvious defects is next. Check the connectors and connections for security, corrosion, and damaged pins. This should include all wiring and connectors for the transmission pressure control solenoids, transmission pump, and PCM. Depending on the specific configuration, the transmission pump may be electrically or mechanically driven.
Advanced Steps
Advanced steps always become very vehicle-specific and require appropriate advanced equipment to operate accurately. These procedures require a digital multimeter and vehicle-specific technical references. You should always obtain troubleshooting data specific to your vehicle before proceeding with advanced steps. Voltage requirements vary depending on the specific vehicle model. Fluid pressure requirements may also vary depending on the transmission design and configuration.
Continuity Checks
Unless otherwise indicated in the technical data, normal readings for wiring and connections should be 0 ohms of resistance. Continuity checks should always be performed with the power disconnected from the circuit to avoid short-circuiting the circuit and causing further damage. Resistance or lack of continuity is an indication of faulty wiring that is open or short-circuited and must be repaired or replaced.
What are the common repairs for this code?
- Replacing the fluid and filter
- Replacing the faulty pressure control solenoid
- Repairing or replacing a faulty transmission pump
- Repairing or replacing the faulty transmission valve body
- Cleaning the passages
- Cleaning corrosion from connectors
- Repairing or replacing faulty wiring
- Flashing or replacing a faulty PCM
Possible misdiagnosis may include:
- Engine misfire issue
- Transmission pump malfunction
- Internal transmission problem
- Transmission problem
Hopefully, the information contained in this article will help you fix the issue with your P0966 pressure control solenoid diagnostic trouble code(s). This article is strictly for informational purposes, and specific technical data and service bulletins for your vehicle will always take precedence.