Introduction:

The P1700 diagnostic trouble code (DTC) indicates that the Transmission Control Module (TCM) has requested the Malfunction Indicator Lamp (MIL), commonly known as the check engine light, to illuminate. This signifies that the TCM has detected a fault within the transmission system but is not directly responsible for the specific problem. Instead, it's acting as a messenger, informing the Engine Control Module (ECM) to turn on the MIL and alert the driver to a potential transmission issue that requires attention. Addressing this code promptly is crucial to prevent further damage and ensure optimal vehicle performance.

Table: P1700 Diagnostic Trouble Code (DTC) Breakdown

Topic Description Relevance to P1700
Definition Transmission Control Module (TCM) Requested MIL Illumination. The core meaning of the code; signifies the TCM has detected a transmission fault and requested the ECM to activate the MIL. This is not the root cause, but rather an indicator of a deeper problem within the transmission.
Affected Systems Automatic Transmission System, Engine Control System (specifically ECM/PCM). P1700 directly involves the communication between the TCM and the ECM/PCM. The TCM detects the transmission issue, and the ECM/PCM is responsible for illuminating the MIL. Other transmission components are indirectly affected as they are the source of the detected fault.
Common Symptoms Illuminated MIL (Check Engine Light), Possible transmission performance issues (hard shifting, slipping, delayed engagement), Limp mode (reduced power and limited gear selection). The primary symptom is the illuminated MIL. The presence and severity of other symptoms depend on the underlying transmission fault that triggered the P1700 code. Limp mode is a protective mechanism to prevent further damage.
Possible Causes Internal transmission failures (worn clutches, damaged solenoids, valve body issues), Transmission fluid level issues, Faulty sensors (transmission speed sensors, temperature sensors), Wiring harness issues (damaged wires, loose connections), TCM malfunction (less common). P1700 is a general code, meaning the actual cause can be varied. It requires further diagnostics to pinpoint the specific problem. Internal transmission failures are often the culprit, but simpler issues like low fluid or faulty sensors should be ruled out first. TCM failure is a last resort diagnosis.
Diagnostic Steps Scan for other transmission-specific DTCs, Inspect transmission fluid level and condition, Check wiring and connectors, Test sensors, Perform transmission internal diagnostics (pressure tests, solenoid tests), Consult vehicle-specific repair manual. Prioritize scanning for more specific transmission codes (e.g., codes related to solenoids, gear ratios, or pressure). The P1700 code acts as a starting point. The repair manual provides specific testing procedures and acceptable ranges for sensors and other components.
Related DTCs Any transmission-specific DTCs (e.g., P0700 series, P07xx, P08xx, P09xx codes), U0100 (Lost Communication with ECM/PCM), U0101 (Lost Communication with TCM). These codes provide more detailed information about the specific transmission problem. Communication errors (U codes) can sometimes trigger P1700 if the TCM cannot properly communicate with the ECM/PCM. Addressing these related codes is often necessary to resolve the P1700.
Tools Required OBD-II scanner, Multimeter, Wiring diagram, Transmission fluid dipstick (if applicable), Pressure gauge (for transmission pressure testing), Vehicle-specific repair manual. An OBD-II scanner is essential for reading the DTCs. A multimeter is needed for testing sensor circuits and wiring continuity. The repair manual provides valuable information on testing procedures and component locations. Specialized tools may be required for internal transmission diagnostics.
Severity Moderate to High. The severity depends on the underlying transmission problem. Ignoring P1700 can lead to further transmission damage and potentially complete transmission failure, resulting in costly repairs or replacement. Addressing the issue promptly can prevent escalation.
Potential Repair Costs Variable; can range from minor repairs (e.g., sensor replacement, fluid change) to major repairs (e.g., transmission rebuild or replacement). The cost depends entirely on the root cause. A simple sensor replacement might be relatively inexpensive, while a transmission rebuild can be a significant expense. Getting an accurate diagnosis is key to estimating the repair cost.
TCM Location Varies by vehicle make and model; typically located inside the vehicle cabin (under the dash, under the seat) or within the engine compartment.

Detailed Explanations:

Definition: The P1700 code, "Transmission Control Module (TCM) Requested MIL Illumination," is a signal indicating the TCM has detected a problem within the transmission system severe enough to warrant alerting the driver. It's not the specific issue itself, but rather a request to the ECM/PCM to turn on the check engine light.

Affected Systems: The primary systems involved are the automatic transmission system and the engine control system (specifically the ECM/PCM). The TCM monitors the transmission's operation and, upon detecting a fault, sends a signal to the ECM/PCM. The ECM/PCM then illuminates the MIL.

Common Symptoms:

  • Illuminated MIL (Check Engine Light): This is the most obvious symptom.
  • Possible transmission performance issues: These can include hard or erratic shifting, slipping during acceleration, delayed engagement when shifting into drive or reverse, or complete failure to shift.
  • Limp mode (reduced power and limited gear selection): This is a safety feature that limits the vehicle's speed and gear selection to protect the transmission from further damage.

Possible Causes: Identifying the root cause of P1700 can be complex, as it's a general indicator. Here's a breakdown of potential issues:

  • Internal transmission failures: This is a broad category encompassing problems like worn clutches and bands, damaged solenoids, valve body issues (stuck valves, worn bores), and broken hard parts (gears, shafts).
  • Transmission fluid level issues: Low fluid level can cause slipping and overheating, leading to transmission damage and potentially triggering the P1700 code. Overfilled fluid can also cause problems.
  • Faulty sensors: Transmission speed sensors (input and output), transmission temperature sensors, and other sensors provide critical data to the TCM. If these sensors fail or provide inaccurate readings, the TCM may incorrectly detect a problem.
  • Wiring harness issues: Damaged wires (frayed, broken), loose connections, or corrosion in the wiring harness can disrupt the signals between the sensors, TCM, and ECM/PCM.
  • TCM malfunction: Although less common, the TCM itself can fail, leading to false error readings and a P1700 code. This is usually diagnosed after ruling out other potential causes.

Diagnostic Steps: A systematic approach is crucial for diagnosing P1700:

  1. Scan for other transmission-specific DTCs: This is the most important step. Use an OBD-II scanner to retrieve all stored DTCs, paying close attention to any codes related to specific transmission components or functions (e.g., solenoid codes, gear ratio codes, pressure codes). These codes will provide clues about the underlying problem.
  2. Inspect transmission fluid level and condition: Check the fluid level using the dipstick (if equipped) or the fill plug. The fluid should be at the correct level and should appear clean and bright red or pink. Dark, burnt, or metallic-contaminated fluid indicates a serious problem within the transmission.
  3. Check wiring and connectors: Visually inspect the wiring harness and connectors associated with the transmission, sensors, and TCM. Look for any signs of damage, corrosion, or loose connections. Use a multimeter to check for continuity and voltage at the sensor connectors.
  4. Test sensors: Use a multimeter and a vehicle-specific repair manual to test the resistance and voltage output of the transmission speed sensors, temperature sensors, and other relevant sensors. Compare the readings to the specifications in the repair manual.
  5. Perform transmission internal diagnostics: This may involve pressure tests, solenoid tests, and other specialized procedures to evaluate the internal components of the transmission. These tests typically require specialized tools and knowledge.
  6. Consult vehicle-specific repair manual: This is an invaluable resource for troubleshooting P1700. The repair manual provides detailed diagnostic procedures, wiring diagrams, component locations, and specifications for your specific vehicle.

Related DTCs:

  • Any transmission-specific DTCs (e.g., P0700 series, P07xx, P08xx, P09xx codes): These codes provide more detailed information about the specific transmission problem that triggered the P1700.
  • U0100 (Lost Communication with ECM/PCM): This code indicates a communication failure between the TCM and the ECM/PCM, which can sometimes trigger P1700.
  • U0101 (Lost Communication with TCM): This code indicates a communication failure with the TCM itself.

Tools Required:

  • OBD-II scanner: To read and clear DTCs.
  • Multimeter: To test sensor circuits and wiring continuity.
  • Wiring diagram: To trace wiring and identify component locations.
  • Transmission fluid dipstick (if applicable): To check fluid level.
  • Pressure gauge (for transmission pressure testing): For more in-depth diagnostics.
  • Vehicle-specific repair manual: For detailed procedures and specifications.

Severity: The severity of P1700 is moderate to high. While the code itself doesn't pinpoint the exact problem, it indicates a transmission issue that needs attention. Ignoring the code can lead to further transmission damage and potentially complete failure, resulting in costly repairs or replacement.

Potential Repair Costs: Repair costs vary greatly depending on the underlying cause.

  • Minor repairs (e.g., sensor replacement, fluid change): \$100 - \$500
  • Valve body repair or replacement: \$500 - \$1500
  • Transmission rebuild: \$2000 - \$4000
  • Transmission replacement: \$3000 - \$7000+

TCM Location: The TCM location varies by vehicle make and model. It's typically located inside the vehicle cabin (under the dash, under the seat) or within the engine compartment. Consult the vehicle-specific repair manual for the exact location.

Frequently Asked Questions:

  • What does the P1700 code mean? The P1700 code means the Transmission Control Module (TCM) has detected a fault in the transmission system and requested the Engine Control Module (ECM) to turn on the check engine light. It indicates a problem that requires further investigation.

  • Can I drive my car with a P1700 code? It depends on the severity of the underlying transmission problem. If the transmission is shifting normally, you might be able to drive it for a short distance, but it's best to get it checked out as soon as possible to avoid further damage. If the transmission is slipping or shifting erratically, it's best to avoid driving it.

  • Is the P1700 code serious? Yes, P1700 indicates a potential transmission problem that should be addressed promptly. Ignoring it can lead to more significant and costly damage.

  • Will replacing the TCM fix the P1700 code? Not necessarily. Replacing the TCM should only be done after ruling out all other possible causes, as the TCM is often not the root of the problem. Focus on diagnosing the underlying transmission fault first.

  • How do I clear the P1700 code? You can clear the code using an OBD-II scanner, but it will likely return if the underlying problem is not fixed. Fix the issue first, then clear the code.

Conclusion:

The P1700 code is a signal from your vehicle's TCM indicating a potential transmission problem. Thoroughly diagnose the issue by scanning for other DTCs and inspecting the transmission system components to determine the root cause and prevent further damage.