P1955 Code: Complete DIY Repair Guide

The P1955 code is a diagnostic trouble code (DTC) that indicates a communication issue between the glow plug module and the powertrain control module (PCM). This code is particularly relevant for diesel engines, where glow plugs are essential for starting and maintaining engine temperature. When the P1955 code is triggered, it often results in reduced engine performance and may cause the vehicle to enter limp mode, limiting speed and power to prevent further damage.

Symptoms of P1955 Code

When experiencing a P1955 code, vehicle owners may notice several symptoms, including:

• Check Engine Light: The most common indication of trouble codes.
• Limp Mode Activation: The vehicle may enter limp mode, restricting power and speed.
• Difficulty Starting: Especially in cold weather, as glow plugs are crucial for diesel engine ignition.
• Rough Idle: The engine may run unevenly or misfire.
• Increased Emissions: Poor combustion due to faulty glow plugs can lead to higher emissions.

Technical Explanations

The P1955 code specifically refers to a communication failure between the glow plug module and the PCM. The glow plug module controls the operation of the glow plugs, which preheat the combustion chamber for easier starting. If the PCM cannot communicate effectively with this module, it cannot regulate the glow plug operation properly.

How Glow Plugs Work

Glow plugs are heating elements that assist in starting diesel engines. They heat up to facilitate combustion at startup, especially in cold conditions. If any component involved in this system fails, it can trigger a fault code like P1955.

Step-by-Step Diagnosis

To diagnose the P1955 code effectively, follow these steps:

1. Scan for Codes: Use an OBD-II scanner to confirm the presence of the P1955 code and check for any additional codes.
2. Visual Inspection:

• Check wiring and connectors related to the glow plug module for signs of damage or corrosion.
• Inspect the glow plugs themselves for wear or failure.

1. Test Glow Plug Operation:

• Measure resistance across each glow plug. A typical reading should be between 0.5 to 2 ohms.
• If any glow plug shows infinite resistance, it is likely faulty.

1. Check Glow Plug Module:

• Verify that the glow plug module is receiving power from the PCM.
• Test the output signal from the module using a multimeter.

1. Inspect PCM Connections:

• Ensure that all connections to the PCM are secure and free from corrosion.
• Look for any signs of water intrusion or shorts.

1. Perform Software Update:

• Check if there are any software updates available for your vehicle’s PCM that may resolve communication issues.

Solution Methods

Depending on your diagnosis, here are potential solutions:

• Replace Faulty Glow Plugs: If testing reveals that one or more glow plugs are defective, replace them with new ones.
• Repair Wiring Issues: If you find damaged wires or connectors, repair or replace them as necessary.
• Replace Glow Plug Module: If the module is confirmed faulty after testing, replacing it will restore proper function.
• Reprogram or Replace PCM: In cases where software issues persist, consider reprogramming or replacing the PCM if it is found to be defective.

Cost Estimates

Repair costs can vary based on parts and labor costs in your region:

• Glow Plugs: $20-$100 each (labor costs vary)
• Glow Plug Module Replacement: $100-$300 (including labor)
• PCM Replacement/Programming: $500-$1500 depending on make and model

Warnings and Recommendations

• Always disconnect the battery before working on electrical components to avoid shorts.
• If you are not comfortable performing these diagnostics or repairs yourself, seek professional assistance to avoid further damage to your vehicle.

Closing Paragraph

The P1955 code can be a significant issue for diesel vehicle owners, impacting performance and drivability. By understanding its meaning and following a systematic approach to diagnosis and repair, DIY mechanics can effectively address this trouble code. Regular maintenance of electrical components related to the glow plug system can also help prevent future occurrences of this issue.

Frequently Asked Questions About P1955

• What does a P1955 code mean?
  The P1955 code indicates a communication error between the glow plug module and the powertrain control module.
• Can I drive my vehicle with a P1955 code?
  It is not advisable as it may lead to reduced engine performance and increased emissions.
• What causes a P1955 code?
  Common causes include faulty glow plugs, wiring issues, or a defective glow plug module.
• How do I clear a P1955 code?
  You can clear it using an OBD-II scanner after addressing the underlying issue.
• Is it safe to replace glow plugs myself?
  If you have basic mechanical skills and tools, you can replace them safely; otherwise, consult a professional.
• What should I check first when diagnosing a P1955?
  Start with checking for additional trouble codes and perform a visual inspection of wiring and connectors.
• How much does it cost to fix a P1955 code?
  The cost can range from $100 to $1500 depending on whether you need to replace parts like glow plugs or the PCM.
• When should I seek professional help for a P1955 code?
  If you’re unable to diagnose or fix the issue after following standard procedures, it’s best to consult an automotive technician.