|Trouble Code||Fault Location||Probable Cause|
|P0966||Pressure control (PC) solenoid B -control circuit low||Wiring, short to earth, pressure control solenoid, ECM/PCM/TCM|
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What Does Code P0966 Mean?
In the modern automatic transmission, hydraulic pressure is generated in the pump, usually located at the front of the transmission, driven by the engine via the torque converter housing. Channels direct automatic transmission fluid to the valve body, which contains the shift solenoid (SS) valves and pressure control solenoid (PCS) valves. The transmission control module (TCM) controls the activation and modulation of the various solenoid valves, depending on driver demand and driving conditions. The TCM may or may not be integrated into the ECM (engine control module).
Electronically-controlled valves are used to shift and maintain gears. The SS valves control the activation and deactivation of clutches, brakes, and bands inside the transmission, effecting the engagement and disengagement of whatever gear is desired or required by the driver and operating conditions. One or more PCS valves control hydraulic pressure inside the transmission, which can affect how shift engagements occur, whether slow and soft or hard and fast.
If the TCM detects a problem with one of the valves, such as a short circuit, it commands the malfunction indicator lamp (MIL) “On” and stores a diagnostic trouble code (DTC) in system memory. DTC P0966 is defined as “Pressure Control Solenoid ‘B’ Control Circuit Low,” though different automakers may have slightly different definitions.
Note: Circuit Low Input codes are often the result of low battery voltages (that can have many possible causes), bad connections across electrical connectors or previously repaired wiring, as well as corrosion in electrical connectors. Other possible causes of low input voltages include poor installation of aftermarket components, poor quality aftermarket components like fuses, relays, and switches, and modification of the electrical system that could include the use of conductors that are not rated for use in a particular application. However, poor connections often result in high resistances in some parts of the circuit, which is why it is important to perform resistance and continuity checks during the diagnostic procedure.
What are the common causes of code P0966 ?
Depending on year, make, and model, DTC P0966 may have number of causes. Here are some of the most common.
- Harness – Usually, external damage or a poor connection can cause this problem. Road damage, poor repair practices, misrouted wire harnesses, or corrosion are par for the course.
- PCS Valve – Somewhat less common, the coil in the pressure control solenoid valve itself may be faulty, causing a short circuit. You’ll most likely need to remove the automatic transmission oil pan, filter, and valve body to access the valve.
What are the symptoms of code P0966 ?
If the TCM is unable to control the pressure control solenoid, this usually results in transmission problems, which may vary depending on year, make, and model. Some vehicles may simply boost transmission line pressure to an unregulated maximum, which may lead to harsh shifting or banging into gear, even on gentle acceleration. Other vehicles may experience missing gears or limited performance. You should still be able to drive the vehicle, but it won’t be very comfortable. If your transmission is bang-shifting, you should have it repaired immediately, as this could actually cause further and more expensive damage to the transmission and driveline.
How do you troubleshoot code P0966 ?
Because this DTC refers to a circuit problem, you’ll need a DVOM (digital multimeter) and a vehicle-specific EWD (electrical wiring diagram) to diagnose it from a source such as All Data DIY. Because the PCS valves are typically located inside the transmission, repairs may involve opening up the transmission, which is complicated and messy. Some DIYers opt to visit the professionals when dealing with internal transmission work for this reason.
- Harness Check – Check over the wire harness going from the TCM to the transmission, looking for any obvious damage, such as from road debris or chafing. Check the TCM and transmission connectors, as well as any sub-harness connectors, for corrosion, evidence of water entry, or damaged pins. Repair as necessary and ensure all connectors are seated properly.
- Circuit Check – Again, this check will require intimate knowledge of your EWD, so make sure your EWD is specific to your year, make, model, engine, and transmission. Most PCS valves are wired to activate in two directions, that is, the TCM can activate them forwards or backwards to regulate pressure. That being said, you can start by disconnecting the TCM connector and measuring the resistance across the terminals. Generally, you can expect to measure 20 Ω to 30 Ω, depending on the temperature of the transmission.
- If resistance is as expected, suspect an intermittent problem or a fault in the TCM. Recheck the harnesses and connectors for loose connections or broken wires, which may cause short circuit problems when the vehicle is in motion. Do not condemn the TCM until you have checked and eliminated absolutely everything else and had it checked by a professional, preferably one who specializes in automatic transmissions.
- If resistance is not as expected, in this case anything over 100 Ω or a short circuit, repeat the test at the transmission connector.
- If the resistance is not as expected, suspect a PCS valve failure or transmission internal wire harness failure, the latter being less common.
- If the resistance is as expected, suspect a short circuit in the wire harness somewhere between the TCM and transmission. Repair as necessary.
Codes Related to P0966
- P0745 Pressure Control Solenoid “A”
- P0746 Pressure Control Solenoid “A” Performance or Stuck Off
- P0747 Pressure Control Solenoid “A” Stuck On
- P0748 Pressure Control Solenoid “A” Electrical
- P0749 Pressure Control Solenoid “A” Intermittent
- P0775 Pressure Control Solenoid “B”
- P0776 Pressure Control Solenoid “B” Performance or Stuck off
- P0777 Pressure Control Solenoid “B” Stuck On
- P0778 Pressure Control Solenoid “B” Electrical
- P0779 Pressure Control Solenoid “B” Intermittent
- P0795 Pressure Control Solenoid “C”
- P0796 Pressure Control Solenoid “C” Performance or Stuck off
- P0797 Pressure Control Solenoid “C” Stuck On
- P0798 Pressure Control Solenoid “C” Electrical
- P0799 Pressure Control Solenoid “C” Intermittent
- P0960 Pressure Control Solenoid “A” Control Circuit/Open
- P0961 Pressure Control Solenoid “A” Control Circuit Range/Performance
- P0962 Pressure Control Solenoid “A” Control Circuit Low
- P0963 Pressure Control Solenoid “A” Control Circuit High
- P0964 Pressure Control Solenoid “B” Control Circuit/Open
- P0965 Pressure Control Solenoid “B” Control Circuit Range/Performance
- P0966 Pressure Control Solenoid “B” Control Circuit Low
- P0967 Pressure Control Solenoid “B” Control Circuit High
- P0968 Pressure Control Solenoid “C” Control Circuit Open
- P0969 Pressure Control Solenoid “C” Control Circuit Range/Performance
- P0970 Pressure Control Solenoid “C” Control Circuit Low
- P0971 Pressure Control Solenoid “C” Control Circuit High