Seeing a check engine light is never fun. If your scanner shows the P0746 OBD-II trouble code, it means your car’s computer has detected a problem with the transmission’s pressure control solenoid. This code specifically points to an electrical issue with the solenoid circuit or its performance, which can affect your vehicle’s shifting and overall driveability.
P0746 OBD-II Trouble Code: Pressure Control Solenoid
This code is a generic powertrain code, meaning it applies to many makes and models. The pressure control solenoid is a crucial electronic valve inside your automatic transmission. Its job is to regulate the hydraulic fluid pressure that controls when and how the transmission shifts gears. When the Powertrain Control Module (PCM) sees a voltage or signal from this solenoid that is outside the expected range, it stores the P0746 code.
What Does the Pressure Control Solenoid Do?
Think of your transmission’s hydraulic system like the plumbing in your house. The pressure control solenoid is an electronically controlled valve in that system. The PCM tells it how much to open or close.
By adjusting the valve, it precisely controls the pressure of the transmission fluid. This fluid pressure is what engages clutches and bands to change gears. A faulty solenoid can lead to:
- Harsh or slipping shifts
- Failure to shift into certain gears
- Delayed shifting
- Increased transmission temperature
- Reduced fuel economy
Common Symptoms of a P0746 Code
You might notice one or more of these signs before or after the check engine light comes on. The symptoms can vary in severity.
- Illuminated Check Engine Light: This is the most common first sign.
- Transmission Slipping: The engine RPMs may flare up but the vehicle doesn’t accelerate properly.
- Harsh or Jerky Shifting: Gear changes feel rough or bang into place.
- Delayed Shifting: There’s a long pause when the transmission should shift.
- Limp Mode: The PCM may force the transmission to stay in only one gear (often 2nd or 3rd) to prevent damage.
- Poor Fuel Economy: Inefficient shifting leads to more fuel being used.
What Causes the P0746 Trouble Code?
Several issues can trigger this code. They range from simple electrical faults to serious internal transmission problems. Here’s a list of common culprits.
- Faulty Pressure Control Solenoid: The solenoid itself can wear out or fail internally.
- Open or Shorted Wiring: Damaged wires to or from the solenoid are a frequent cause.
- Poor Electrical Connection: A corroded, loose, or damaged connector at the solenoid.
- Low or Degraded Transmission Fluid: Old, burnt, or insufficient fluid can’t build proper pressure.
- Clogged Transmission Filter: A restricted filter starves the hydraulic system, affecting solenoid operation.
- Internal Transmission Damage: Worn clutches, seals, or a faulty valve body can mimic solenoid issues.
- Failed PCM: This is rare, but the computer itself could be malfunctioning.
How to Diagnose a P0746 Code
Diagnosis requires a systematic approach. Always start with the simplest and least expensive possibilities first. Safety First: Ensure the vehicle is on a level surface with the parking brake firmly engaged.
Step 1: Check the Transmission Fluid
This is your first and most critical step. Locate the transmission dipstick (if equipped), usually near the back of the engine bay.
- Start the engine and let it reach normal operating temperature.
- With the engine running and the parking brake on, cycle through each gear (P-R-N-D-L) briefly, then return to Park.
- Pull the dipstick, wipe it clean, reinsert it fully, and pull it out again to check the level.
- Check both the level and the condition. The fluid should be at the “Full” mark and be a clear red color. Brown, dark, or burnt-smelling fluid indicates a problem.
If the fluid is low, top it up with the correct type specified in your owner’s manual. If it’s very dark or burnt, a fluid change may be needed, but this could also point to internal wear.
Step 2: Scan for Additional Codes
Use your OBD-II scanner to check for any other codes. Codes like P0748 or those related to other solenoids or speed sensors can provide valuable clues about a larger issue.
Step 3: Visual Inspection of Wiring and Connectors
You’ll need to locate the transmission wiring harness and the solenoid’s electrical connector. This often requires safely raising the vehicle.
- Look for any wires that are chafed, melted, or chewed by animals.
- Inspect the solenoid connector for corrosion, bent pins, or looseness.
- Check that the connector is securely clicked into place.
Step 4: Electrical Testing
This step requires a digital multimeter (DMM) and possibly a wiring diagram for your specific vehicle.
- Check for Power and Ground: With the connector disconnected, use the DMM to check for battery voltage and a good ground at the harness side of the connector with the key on.
- Check Solenoid Resistance: Set your DMM to Ohms. Measure the resistance across the two terminals of the solenoid itself (you may need to unbolt it). Compare the reading to your vehicle’s service specification. A reading of zero (short) or infinite (open) means the solenoid is bad.
- Check for Shorts to Ground: With the wiring harness disconnected, check that neither wire from the PCM to the solenoid is shorted to the vehicle’s chassis.
Step 5: Professional Diagnostics
If the wiring and solenoid test okay, the problem may be internal. A mechanic might use a scan tool to command the solenoid on and off while monitoring the pressure with a gauge. They can also check for issues within the transmission valve body, which houses the solenoids.
How to Fix the P0746 Code
The fix depends entirely on the root cause you found during diagnosis. Here are the common repairs.
Fix 1: Addressing Fluid and Filter Issues
If the fluid was low or dirty, topping it up or performing a transmission fluid and filter change might clear the code. After the service, clear the code with your scanner and take a test drive to see if it returns. Remember, severely burnt fluid often indicates existing internal damage.
Fix 2: Repairing Wiring or Connections
If you found damaged wires, repair them properly with solder and heat shrink tubing—do not just use twist connectors. Clean any corroded connector pins with electrical contact cleaner. Ensure the connection is tight and waterproof.
Fix 3: Replacing the Pressure Control Solenoid
If the solenoid fails the resistance test, it needs replacement. On some vehicles, this is an external repair. On many others, it requires dropping the transmission oil pan to access the solenoid, which is mounted on the valve body.
- Drain the transmission fluid.
- Remove the transmission pan.
- Unbolt the old solenoid and disconnect its electrical connector.
- Install the new solenoid with a new seal/gasket if provided.
- Reinstall the pan with a new gasket, refill with fresh fluid, and test.
Fix 4: Internal Transmission Repair
If the valve body is clogged or damaged, or if there is internal wear (like worn seals or clutches), a major transmission repair or rebuild may be necessary. This is a complex and costly job best left to a professional transmission specialist.
Is It Safe to Drive With a P0746 Code?
It is not recommended. Driving with this code can lead to further transmission damage. The improper pressure can cause clutches to slip and overheat, leading to complete transmission failure. If the vehicle goes into limp mode, your mobility is severely limited. Have the vehicle diagnosed as soon as possible.
Estimated Repair Costs
Costs vary widly based on the cause and your vehicle model.
- Transmission Fluid Service: $100 – $300
- Pressure Control Solenoid (Part Only): $50 – $250
- Solenoid Replacement Labor: $200 – $600 (more if the transmission pan is difficult to access)
- Valve Body Repair/Replacement: $500 – $1,200
- Transmission Rebuild: $2,000 – $4,000+
FAQs About the P0746 Code
Can I reset the P0746 code and have it stay off?
You can clear the code with a scanner, but if the underlying problem isn’t fixed, it will almost certainly come back within a few drive cycles. Clearing the code without fixing the issue is just a temporary measure.
Is P0746 a serious code?
Yes, it should be taken seriously. Ignoring it can lead to severe and expensive transmission damage. It directly affects a critical control system for your transmission.
What’s the difference between P0746 and P0748?
Both relate to the pressure control solenoid. P0746 typically indicates an electrical performance or circuit issue (like a short or open). P0748 usually points to an electrical current or voltage problem in the solenoid control circuit. They are closely related and often diagnosed similarly.
Can a bad battery cause transmission solenoid codes?
In some cases, yes. A weak battery or poor alternator output can cause low system voltage. The PCM and solenoids require stable voltage to operate correctly. Fluctuating voltage can sometimes trigger electrical fault codes.
Will a bad pressure control solenoid always trigger a code?
Not always immediately, but usually yes. The PCM is constantly monitoring the solenoid’s feedback signal. A significant failure will be detected and stored as a code. Intermittent problems might cause symptoms before the light comes on.
Dealing with a P0746 OBD-II trouble code requires patience and careful diagnosis. Starting with a simple fluid check and visual inspection can often reveal the problem without the need for major repairs. However, given the importance of the transmission to your vehicle’s operation, don’t hesitate to seek help from a qualified technician if you’re unsure at any step. Addressing this code promptly is the best way to protect your transmission and your wallet from more serious damage down the road.