Encountering the OBD2 code P0700 can be unsettling, especially when your check engine light illuminates unexpectedly. This code signals a problem within your vehicle’s transmission control system, but it’s not always a cause for immediate panic. Understanding what P0700 means, its potential causes, and possible solutions can empower you to address the issue effectively, potentially saving time and money on unnecessary repairs.
What Does OBD2 Code P0700 Mean?
The OBD2 (On-Board Diagnostics II) code P0700 is a generic trouble code that indicates “Transmission Control System Malfunction.” Essentially, your car’s Engine Control Module (ECM) has received a signal from the Transmission Control Module (TCM) indicating that a fault has been detected within the transmission system.
It’s important to understand that P0700 itself is not a specific problem, but rather a notification that there’s a deeper issue within the TCM. When the ECM detects P0700, it triggers the check engine light to alert you to the potential transmission problem. To get to the root cause, further investigation into the transmission system is necessary, often requiring a scan tool capable of reading TCM codes.
Symptoms Associated with OBD2 Code P0700
While P0700 primarily indicates a TCM malfunction, you might experience various symptoms depending on the specific underlying issue. Some common symptoms include:
- Check Engine Light is illuminated: This is the most direct symptom, as the P0700 code is designed to trigger the malfunction indicator lamp.
- Transmission shifting problems: These can range from harsh or erratic shifting, delayed engagement, or getting stuck in a particular gear (often second gear limp mode).
- Reduced performance or fuel economy: Inefficient transmission operation can lead to decreased engine performance and lower gas mileage.
- Inability to shift into certain gears: In some cases, the transmission might refuse to shift into certain gears, limiting vehicle speed and power.
- Speedometer malfunction (in some cases): If the output speed sensor is involved, you might notice erratic or non-functional speedometer readings.
It’s worth noting that in some instances, as seen in the original forum post, the P0700 code might appear intermittently, and the symptoms might seem to disappear temporarily, only to return later.
Potential Causes of OBD2 Code P0700
Pinpointing the exact cause of P0700 requires a systematic approach. Based on expert advice and community experiences, potential causes can include:
- Faulty Transmission Input or Output Speed Sensors: These sensors monitor the speed of the transmission’s input and output shafts. Malfunctions can disrupt gear shifting and trigger P0700.
- Transmission Control Module (TCM) Issues: While P0700 indicates a TCM fault, the TCM itself might be malfunctioning due to internal failures or electrical problems.
- Relay Problems: Relays provide power to the TCM and transmission components. A failing or intermittent relay can disrupt the system’s operation.
- Fuse Problems: Similar to relays, fuses protect circuits. A blown fuse in the TCM or transmission circuit can cause a P0700 code.
- Solenoid Issues: Transmission solenoids control the flow of transmission fluid, enabling gear changes. Faulty solenoids can lead to shifting problems and P0700.
- Wiring and Connector Problems: Damaged, corroded, or loose wiring and connectors in the transmission control system can cause intermittent or permanent faults.
- Low Transmission Fluid Level or Condition: While less directly related to electrical faults, low or contaminated transmission fluid can cause transmission issues that might indirectly trigger a P0700 code in some vehicles.
Troubleshooting and Fixing OBD2 Code P0700
Addressing P0700 involves a step-by-step diagnostic process. Here are some troubleshooting steps, drawing from both expert recommendations and community experiences in the original forum:
-
Check for other OBD2 Codes: Use an OBD2 scanner to read all stored codes. P0700 is a general code, and there are likely more specific transmission codes stored in the TCM. These additional codes are crucial for pinpointing the exact problem (e.g., codes related to specific sensors or solenoids).
-
Inspect Transmission Fluid: Check the transmission fluid level and condition. Low or dirty fluid can sometimes contribute to transmission issues. Refer to your vehicle’s owner’s manual for the correct procedure and fluid type.
-
Check TCM and Starter Relays: Locate the Power Distribution Center (PDC) under the hood. Identify the TCM relay and starter relay (consult your owner’s manual for location). Try swapping these relays temporarily, as suggested in the forum. If the issue improves after swapping, replace the potentially faulty relay. Note: This is a diagnostic step, not a permanent fix if a relay is indeed failing.
-
Inspect TCM Fuse: Locate the TCM fuse in the PDC or fuse box (again, refer to your manual). Check if the fuse is blown. If it is, replace it with a fuse of the same amperage. If the fuse blows again immediately, there’s likely a short circuit in the system that needs further investigation. Note: As seen in the forum, temporarily removing and reinserting the TCM fuse might clear the code, but this is not a reliable fix and doesn’t address the underlying problem.
-
Evaluate Input and Output Speed Sensors: If you suspect sensor issues (especially if you experience symptoms like getting stuck in second gear or speedometer problems), consider inspecting or replacing the input and output speed sensors. These are typically located on the transmission housing. As mentioned in the forum, if your speedometer works when the transmission issue occurs, the input sensor is more likely the culprit. If the speedometer also malfunctions, the output sensor might be the cause.
-
Professional Scan and Diagnosis: If the above steps don’t resolve the issue, it’s highly recommended to seek professional diagnosis. A qualified mechanic with a professional-grade scan tool can access the TCM and retrieve specific transmission fault codes, perform advanced diagnostics, and pinpoint the root cause of the P0700 code. They can also properly test sensors, solenoids, wiring, and the TCM itself.
When to Consult a Professional Mechanic
While some basic troubleshooting steps like checking fuses and relays can be done by car owners, diagnosing and repairing transmission issues related to P0700 often requires specialized knowledge and equipment.
It’s advisable to consult a professional mechanic in the following situations:
- You are uncomfortable working on your vehicle’s electrical or transmission systems.
- You cannot retrieve specific TCM codes with your OBD2 scanner.
- Replacing fuses or relays does not resolve the issue.
- You suspect sensor or TCM problems.
- The transmission symptoms are severe or persistent.
Ignoring a P0700 code and associated transmission problems can lead to further damage and more costly repairs down the line. Addressing the issue promptly and correctly is essential for maintaining your vehicle’s reliability and performance.
