If your Honda’s check engine light is on and you see the code P0843, you’re probably looking for answers. This article covers everything about the P0843 Honda error code, from what it means to how you can fix it. This transmission-related code is serious, but understanding it is the first step to getting your car running smoothly again.
Ignoring this code can lead to bigger, more expensive problems. Let’s look at what this code is telling you and what your next steps should be.
Everything About the P0843 Honda Error Code!
The P0843 is a diagnostic trouble code (DTC) that stands for “Transmission Fluid Pressure Sensor/Switch ‘A’ Circuit High Input.” It’s specific to Honda and Acura vehicles. In simple terms, your car’s computer (the PCM) is seeing a voltage signal from a specific transmission sensor that is higher than the normal expected range.
This sensor is crucial. It monitors the hydraulic pressure inside your automatic transmission. The PCM uses this data to control shift timing, shift firmness, and the operation of the torque converter clutch. When the signal is off, your transmission can’t operate correctly.
What Does the Transmission Fluid Pressure Sensor Do?
Think of this sensor as the transmission’s blood pressure monitor. It constantly checks the pressure of the fluid that makes the gears change. This information is sent to the PCM as an electrical signal.
If the pressure is too low, shifts might be soft or slip. If it’s too high, shifts can be harsh. The P0843 code specifically means the signal is reading too high, which the computer interprets as a problem.
Common Symptoms of the P0843 Code
You might notice one or more of these symptoms when the P0843 code is stored:
- Illuminated check engine light or transmission warning light.
- Harsh or erratic shifting between gears.
- Transmission slipping (engine revs high but car doesn’t accelerate properly).
- Failure to shift into higher gears (like being stuck in 2nd or 3rd gear).
- Reduced fuel economy.
- In some cases, the transmission may go into a fail-safe or “limp” mode. This limits you to only one or two gears to prevent further damage.
Main Causes of the P0843 Code in Hondas
Several issues can trigger this code. Here are the most common culprits, starting with the most frequent:
1. Faulty Transmission Fluid Pressure Sensor
This is the most common cause. The sensor itself has failed internally and is sending an incorrect high voltage signal to the PCM. Over time, heat and vibration inside the transmission can cause these sensors to wear out.
2. Problems in the Sensor’s Wiring or Connector
The wiring harness connected to the sensor can get damaged. Look for:
- Chafed or broken wires.
- Corrosion or moisture in the electrical connector.
- A loose connector that isn’t making good contact.
A short to power in the wiring can easily cause a “high input” signal.
3. Low or Degraded Transmission Fluid
While this code points to an electrical signal issue, low fluid level or old, burnt fluid can affect system pressure and sensor readings. It’s a simple thing to check first and a common oversight.
4. Issues with the Transmission Valve Body
The pressure sensor is often mounted on the transmission valve body. If there is a problem inside the valve body—like a stuck pressure switch valve or a clogged fluid passage—it can create an abnormal pressure condition that the sensor rightfully reports.
5. A Failing PCM (Rare)
It’s not common, but sometimes the powertrain control module itself can malfunction and misread a normal sensor signal. This is usually a last-resort diagnosis after everything else has been ruled out.
How to Diagnose the P0843 Code: A Step-by-Step Guide
Diagnosis requires some mechanical knowledge and tools. Always prioritize safety—use jack stands if lifting the vehicle.
- Scan for Codes: Use an OBD-II scanner to confirm P0843 is present. Check for any other codes that may provide additional clues.
- Check Transmission Fluid: With the engine warm and running, on a level surface, check the transmission dipstick. Is the fluid at the correct level? Assess its condition: it should be reddish and smell slightly sweet, not brown/black or burnt.
- Visual Inspection: Locate the transmission fluid pressure sensor (consult your vehicle’s service manual for its location, often on the side or top of the transmission). Inspect the wiring harness and connector for obvious damage, corrosion, or looseness.
- Test the Sensor and Circuit: This requires a digital multimeter.
- Disconnect the sensor connector.
- With the key on, check for reference voltage (usually 5V) and ground at the harness connector.
- Test the sensor’s resistance. Compare your readings to the specifications in the service manual. An out-of-spec sensor needs replacement.
- Monitor Live Data: If your scanner can read live data, view the transmission fluid pressure sensor voltage while the engine is running. An abnormally high reading (like stuck at 4.8V) with the connector plugged in points to a bad sensor or circuit issue.
Repair Procedures for the P0843 Code
The fix depends on what you find during diagnosis. Here are the common repairs:
Replacing the Transmission Fluid Pressure Sensor
- Gather the correct replacement sensor and a new sealing washer or O-ring.
- Disconnect the negative battery cable for safety.
- Disconnect the sensor’s electrical connector.
- Use the correct socket to uncrew the sensor from the transmission.
- Install the new sensor with its new seal and torque it to specification (do not overtighten).
- Reconnect the electrical connector and the battery.
- Clear the codes with your scanner and test drive the vehicle to see if the code returns.
Repairing Damaged Wiring
If you find damaged wires, they must be properly repaired. Do not just use electrical tape. You should:
- Cut out the damaged section of wire.
- Solder in a new piece of similar gauge wire.
- Seal the connection with heat-shrink tubing.
- Secure the harness so it doesn’t chafe again.
Changing Transmission Fluid and Filter
If the fluid is low or dirty, a fluid change is needed. For many Hondas, this involves dropping the transmission pan to replace the filter and fluid. Some models require a specific Honda ATF fluid—don’t use the wrong type. Refill to the exact level and check for leaks after.
Estimated Repair Costs
Costs vary widely based on the cause and whether you do it yourself or go to a shop.
- Transmission Fluid Pressure Sensor Part: $50 – $150.
- Professional Labor for Sensor Replacement: $150 – $300. The job can take 1-2 hours, as the sensor is often accesible without major disassembly.
- Transmission Fluid Change Service: $100 – $200.
- Valve Body Repair or Replacement: $500 – $1,200+. This is a more involved and expensive repair.
Getting a proper diagnosis from a trusted mechanic is key to avoiding unnecessary repairs.
Can You Drive with the P0843 Code?
It is not recommended. Driving for a short distance to get home or to a repair shop is one thing, but continued driving is risky.
The transmission may be operating incorrectly, causing excessive heat and wear on the clutches and bands. If the vehicle goes into limp mode, your mobility will be severely limited. You risk causing major internal damage that could lead to a full transmission rebuild or replacement—a cost often exceeding $3,000.
Prevention Tips
While sensors can fail randomly, you can take steps to help prevent this issue:
- Follow your Honda’s recommended severe maintenance schedule for transmission fluid changes. Many experts suggest every 60,000 miles, even if the manual says “lifetime.”
- Address any other transmission issues, like small leaks or odd shifts, immediately.
- During routine servicing, ask the technician to inspect transmission-related wiring for any early signs of damage.
FAQs About the Honda P0843 Code
Is P0843 a serious code?
Yes, it is considered serious because it directly affects transmission operation. Ignoring it can lead to costly damage.
What does ‘Circuit High Input’ mean?
It means the voltage signal coming from the sensor to the computer is higher than the maximum expected value under normal operating conditions. This indicates a fault.
Can a bad battery cause a P0843 code?
It’s very unlikely. While low system voltage can cause strange electrical issues, P0843 is typically caused by problems specific to the sensor or its dedicated circuit.
Will disconnecting the battery clear the P0843 code?
It may temporarily clear the check engine light, but the code will remain in the PCM’s memory and the light will almost certainly come back on once the driving cycle is completed and the fault is detected again. The underlying problem must be fixed.
Is the P0843 code the same for all Honda models?
The definition of the code is the same, but the location of the sensor and the exact repair steps can vary between models like the Civic, Accord, CR-V, Odyssey, and Pilots. Always consult repair information for your specific vehicle.
Dealing with a P0843 code can be stressful, but a methodical approach to diagnosis will save you time and money. Start with the simple checks—fluid level and condition, and a visual wiring inspection. From there, testing the sensor and its circuit will usually lead you to the root cause. Remember, addressing this code promptly is the best way to protect your Honda’s transmission and ensure many more reliable miles ahead.