Troubleshooting P0847 Error Code In Your Honda Civic

If your Honda Civic’s check engine light is on and you’ve pulled a P0847 code, you’re likely feeling a bit stressed. This guide will help you understand and fix the Troubleshooting P0847 Error Code in Your Honda Civic, saving you time and money. It’s a common transmission-related issue, but with some patience, many DIYers can handle it.

The P0847 code specifically points to a problem with the transmission fluid pressure sensor/switch “B” circuit. In simpler terms, your car’s computer is getting a signal from a sensor that it doesn’t expect. This sensor monitors hydraulic pressure inside your automatic transmission. Don’t ignore it—addressing it early can prevent more serious transmission damage.

Before you start replacing parts, it’s crucial to follow a logical troubleshooting process. Jumping straight to a new transmission or sensor can be an expensive mistake. This section outlines the systematic approach you should take to accurately diagnose the root cause of the P0847 in your Civic.

What You’ll Need for the Job

Gathering the right tools before you start will make the process smoother. Here’s a basic list:

OBD-II scanner (to read and clear the code)
Digital multimeter
Basic hand tools (wrenches, sockets, screwdrivers)
Jack and jack stands or a vehicle ramp
Safety glasses and gloves
New transmission fluid (if needed, check your owner’s manual for the specific type)
Shop rags or paper towels

Step 1: Check the Transmission Fluid Level and Condition

This is always the first and easiest step. A low fluid level or burnt fluid can cause pressure issues that trigger the P0847 code.

Ensure your car is on level ground and the engine is warmed up to normal operating temperature.
With the engine idling and the parking brake firmly applied, shift the gear selector slowly through each position, pausing briefly, then return to Park.
Pull the transmission dipstick (usually a yellow ring handle near the back of the engine bay), wipe it clean, reinsert it fully, and pull it out again.
Check the level. It should be between the two marks labeled “Hot.” Also, note the fluid’s color and smell. It should be reddish and relatively clear, not dark brown/black or smell burnt.

If the fluid is low, top it up carefully with the correct Honda ATF. If it’s burnt, a fluid change may be in order, but it also signals internal wear.

Step 2: Inspect the Wiring and Connectors

Often, the problem isn’t the sensor itself but the wiring leading to it. Physical damage, corrosion, or a loose connection can cause this code.

Locate the transmission fluid pressure sensor(s). On most Honda Civics, they are mounted on the side of the transmission. Refer to a service manual for your specific year for the exact location.
Carefully unplug the electrical connector to the sensor labeled “B” (usually there are two: A and B).
Look for any signs of corrosion on the terminals, bent pins, or moisture inside the connector.
Follow the wiring harness back a few inches, checking for any chafing, cuts, or melting from exhaust heat.

A simple cleaning of the connector or repairing a broken wire can sometimes solve the problem.

Using a Multimeter to Test the Sensor Circuit

If the wiring looks good, you can test the circuit. With the connector disconnected and the ignition key in the “ON” position (engine off), use your multimeter set to DC Volts.

Check for power. Probe the appropriate terminal in the vehicle-side harness (often a red/blue wire) for 5 volts or 12 volts reference voltage from the PCM.
Check for ground. Probe another terminal (often a black wire) for a good ground connection.
If power and ground are present at the harness, the issue may be the sensor itself.

Step 3: Testing the Transmission Fluid Pressure Sensor Itself

Sensor “B” is typically the one that monitors pressure in specific gears (like 2nd, 3rd, or 5th, depending on the model). You can test its resistance.

Set your multimeter to Ohms (Ω).
With the sensor disconnected, measure the resistance between its two terminals.
Compare your reading to the specifications for your Civic (often found in a service manual; a typical range might be between 5 and 100 ohms, but it varies). A reading of zero (short) or infinite (open) means the sensor is faulty.
You can also sometimes check if the resistance changes smoothly as you apply slight air pressure to the sensor port, but this requires a special tool.

Step 4: Consider Other Potential Causes

If the sensor and its wiring test perfectly fine, the problem might be mechanical. The P0847 code indicates the PCM sees a pressure that doesn’t match its expectations for the current driving conditions. This could mean:

A failing solenoid inside the transmission valve body.
A clogged transmission filter (if applicable to your model).
Worn seals or internal transmission wear affecting hydraulic pressure.
In rare cases, a faulty Powertrain Control Module (PCM) itself.

Diagnosing these issues gets more complex and may require professional scan tools to monitor live data from the sensor while driving.

Step-by-Step Sensor Replacement Guide

If you’ve determined the pressure sensor “B” is faulty, here’s a general guide to replacing it. Remember, procedures can vary by model year.

Disconnect the negative battery terminal for safety.
Locate the sensor on the transmission. You may need to remove an air intake box or other components for access.
Unplug the electrical connector by pressing the locking tab and pulling it straight off.
Using the correct size wrench or socket, carefully unscrew the sensor from the transmission. Be prepared for some fluid to leak out—have a rag ready.
Compare the old and new sensors to ensure they are identical.
Install the new sensor with a new sealing washer or O-ring if provided. Tighten it to the specified torque (do not overtighten, as the housing is often aluminum).
Reconnect the electrical connector and any components you removed.
Reconnect the battery.
Use your OBD-II scanner to clear the P0847 trouble code.
Start the engine, let it idle, and check for leaks. Take the car for a test drive to see if the check engine light stays off.

When to Call a Professional Mechanic

DIY has its limits. You should consider seeking professional help if:

You’re uncomfortable working under the vehicle or with electrical diagnostics.
The code returns immediately after replacing the sensor and verifying wiring.
You notice other transmission symptoms like slipping, harsh shifts, or strange noises.
Live data shows illogical pressure readings, pointing to an internal transmission fault.

A trusted mechanic with a advanced scanner can perform pressure tests and analyze live data to pinpoint internal issues.

FAQs About the P0847 Code

Can I drive my Honda Civic with a P0847 code?

It’s not recommended for the long term. While you might be able to drive short distances, the abnormal pressure can lead to increased wear or sudden transmission failure. Get it diagnosed as soon as possible.

How much does it cost to fix a P0847 code?

Costs vary widely. If it’s just a sensor, parts are $50-$150, plus labor if you don’t DIY. If it’s an internal transmission issue like a solenoid or valve body, repairs can range from $400 to over $1000.

Is the P0847 code serious?

Yes, it should be considered serious because it directly relates to transmission hydraulic pressure. Ignoring it can lead to costly transmission damage down the road.

What’s the difference between sensor A and sensor B?

They monitor pressure in different parts of the transmission circuit or different gear ranges. Your Civic’s service manual will specify which is which for your model. The troubleshooting process for both is very similar.

Will the code clear itself after I fix the problem?

Sometimes, after several drive cycles without the fault reoccurring, the light may turn off, but the code will likely remain in the history. It’s best to clear it with an OBD-II scanner after making the repair to confirm it’s fixed.

Dealing with a P0847 code in your Honda Civic can be a manageable DIY project if you’re methodical. Always start with the simplest checks—fluid level and wiring—before moving to part replacement. Remember, this code is your car’s way of telling you something is wrong with the transmission pressure; listening to it early is the key to preventing a minor issue from becoming a major repair. Take your time, be safe, and use this guide to get your Civic back to running smoothly.