If your check engine light is on and your scanner shows code P1738, you’re likely looking for answers. This article explains the P1738 Honda Accord code, its meaning, and what to do next.
Seeing any check engine light can be stressful. But with the right information, you can understand the problem and find a solution. We’ll break down everything in simple terms, from symptoms to fixes.
P1738 Honda Accord Code
The P1738 code is specific to many Honda and Acura vehicles with automatic transmissions. In simple terms, it points to a problem within the transmission’s gear position monitoring system.
Your car’s computer, the PCM, monitors the actual gear you’re in. It compares this to where it thinks the gear should be based on sensor data. Code P1738 sets when these two pieces of information don’t match for a certain amount of time.
What Does the P1738 Code Mean?
Specifically, P1738 stands for “Gear Position Switch Circuit Malfunction (Second Gear).” This indicates the Powertrain Control Module (PCM) has detected an illogical signal from the gear position switch or related sensors concerning the second gear operation.
It doesn’t always mean second gear is broken. Instead, it signals that the computer’s expectation and the reported reality are in conflict. This is a safeguard to protect your transmission from potential damage.
Common Symptoms of a P1738 Code
You might notice one or more of these signs when P1738 is active. The check engine light is the most obvious, but other drivability issues often follow.
- Illuminated Check Engine Light (MIL): This is always the first indicator.
- Harsh or Slipping Shifts: The transmission may shift rough, especially into or out of second gear. It might feel like a jerk or a slip.
- Limp Mode Activation: To prevent damage, the PCM may force the transmission into a “limp” or “fail-safe” mode. This often locks the transmission in a single gear (like 2nd or 3rd) to get you home slowly.
- Poor Acceleration: You may notice a lack of power, as the transmission struggles to manage gear changes correctly.
- Incorrect Gear Indicator Display: On your dashboard, the gear selector display (P, R, N, D, etc.) might show the wrong position or flicker.
What Causes the P1738 Code?
Several issues can trigger this code. It’s often related to electrical signals rather than major mechanical failure inside the transmission itself. Here are the most common culprits.
- Faulty Transmission Range Switch (aka Gear Position Switch): This is the most common cause. This switch tells the PCM what gear you’ve selected with the shifter.
- Problems with the Transmission Speed Sensors: Your Accord has multiple speed sensors (like the secondary shaft speed sensor). A faulty sensor sends incorrect RPM data to the PCM.
- Damaged Wiring or Connectors: Corrosion, fraying, or loose connections in the wiring harness to any of these sensors can interrupt the signal.
- Low or Degraded Transmission Fluid: Old, burnt, or low fluid can affect hydraulic pressure and sensor operation, leading to erroneous codes.
- Issues with the Shift Solenoids: While less common, a sticking or failing shift solenoid can cause incorrect gear application.
- PCM Software Glitch or Failure: Rarely, the computer itself may have a software bug or hardware fault causing it to misread data.
How to Diagnose and Fix P1738
Diagnosis requires a systematic approach. Always start with the simple, inexpensive checks before assuming the worst. You’ll need a basic set of tools and an OBD-II scanner.
Step 1: Scan and Record Codes
Use your OBD-II scanner to confirm P1738 is present. Clear the code and take the car for a test drive. See if the code returns immediately or only under certain conditions (like during a 2nd gear shift). Note any other codes that appear alongside it.
Step 2: Check the Transmission Fluid
This is a critical and easy step. With the engine warm and running, check the transmission fluid level using the dipstick. Assess its condition:
- Is it at the correct level?
- Does it smell burnt?
- Is it dark brown or black instead of reddish?
Low or burnt fluid can cause a multitude of issues. A fluid change is sometimes a simple fix if the fluid is old but not severely degraded.
Step 3: Inspect Wiring and Connectors
Visually inspect the wiring harness connected to the transmission, especially near the gear position switch and speed sensors. Look for:
- Chafed or broken wires
- Corroded or loose connectors
- Any signs of damage from heat or road debris
Repair any damaged wiring you find and ensure connections are tight. This solves many intermittent electrical problems.
Step 4: Test the Transmission Range Switch
The gear position switch is often located on the side of the transmission housing. You can test it with a multimeter.
- Locate the switch and disconnect its electrical connector.
- Consult a repair manual for your specific Accord year to find the pinout diagram.
- With the multimeter set to resistance (Ohms), check for continuity between specific pins as you move the shifter through each position (P, R, N, D, etc.).
- The resistance should change (often to zero Ohms for continuity) in each position. No change in a specific position indicates a faulty switch.
Step 5: Test Speed Sensors
Speed sensors can also be tested with a multimeter for resistance. Their values should fall within a specific range (often a few hundred Ohms). A reading of zero (short) or infinite (open) means the sensor is bad. Sometimes, they can be tested for an AC voltage output while spinning the wheels, but this is more advanced.
Step 6: Consider Professional Diagnosis
If you’ve reached this point without finding the issue, the problem may be internal (like a sticking solenoid) or require advanced PCM diagnostics. A professional mechanic with a high-end scan tool can monitor live data from the sensors while driving, which is often the key to pinpointing an intermittent fault.
Common Fixes for P1738
Based on the diagnosis, here are the typical repairs:
- Topping Off or Changing Transmission Fluid: If fluid was low or dirty, this can resolve the issue. Always use Honda-approved ATF.
- Replacing the Transmission Range Switch: This is a very common fix. The part is relatively affordable, and replacement is straightforward for many DIYers.
- Replacing a Speed Sensor: Secondary shaft speed sensor failure is common in Hondas. It’s usually bolted to the transmission and easy to swap.
- Repairing Wiring Harness: Splicing in new wire or replacing a connector can fix the problem.
- Updating PCM Software: A dealer can check for Technical Service Bulletins (TSBs) and reflash the PCM with updated software.
- Transmission Solenoid Replacement: This requires dropping the transmission oil pan. It’s more involved but often cheaper than a full rebuild.
Is It Safe to Drive with a P1738 Code?
It is not recommended to drive for long with this code active. The main risk is that the vehicle may enter limp mode without warning, leaving you with very limited power and mobility. This can be dangerous in traffic.
If the code appears, drive gently and directly to a safe place to diagnose it. If limp mode activates, your top speed will be severely limited. You should arrange for a tow to avoid causing further stress or damage to the transmission.
Estimated Repair Costs
Costs vary widely based on the cause and who does the work.
- Transmission Fluid Service: $100 – $200
- Transmission Range Switch: Part: $50 – $150. Labor: 1-2 hours ($100 – $300).
- Speed Sensor Replacement: Part: $30 – $100. Labor: ~1 hour ($80 – $150).
- Shift Solenoid Replacement: Part: $50 – $200 per solenoid. Labor: 2-4 hours ($200 – $500) as the pan must be dropped.
- Professional Diagnosis: Typically $100 – $150 for diagostic time.
These are estimates. Always get a quote from your trusted mechanic. Catching it early usually leads to a simpler, cheaper fix.
FAQ Section
Can I reset the P1738 code myself?
Yes, you can clear it with an OBD-II scanner. However, if the underlying problem isn’t fixed, the code will come back, usually within one or two drive cycles. Clearing the code alone does not repair the car.
Does P1738 mean my transmission is failing?
Not necessarily. While it’s a transmission-related code, it’s often an electrical or sensor issue, not a sign of immediate internal mechanical failure. Proper diagnosis is key to avoiding unnecessary expensive repairs.
What years of Honda Accord are affected by P1738?
This code is most commonly reported in 6th and 7th generation Honda Accords (model years roughly 1998-2007), especially those with the V6 engine and automatic transmission. However, it can potentially appear in other years and models with similar transmission systems.
Can a bad battery cause transmission codes like P1738?
Yes, a weak battery or poor alternator output can cause low system voltage. This can make sensors act erratically and the PCM to set spurious codes. It’s a good idea to have your battery and charging system tested, especially if you’re having multiple electrical gremlins.
Should I go straight to a transmission shop for P1738?
Not immediately. Start with a general mechanic who is familiar with Hondas. Many fixes for P1738 are external to the transmission and don’t require a specialist. A transmission shop might be more likely to recommend a rebuild than a simple sensor replacement.
Dealing with a P1738 code can be manageable. By starting with the simple checks—fluid, wiring, and the common sensors—you can often find the problem without a major repair bill. Remember, your Honda Accord is giving you a clue with this code, and with patience, you can solve the puzzle and get back to smooth driving.