U1002 on 2005-2008 Infiniti G35: CAN Communication Failure Causes and Fixes

What's Unique About the 2005-2008 Infiniti G35

The G35 platform, particularly the V36 generation (2007-2008), is highly susceptible to water leaks from clogged sunroof drains. These drains can get plugged with debris or the firewall grommet can shrink, causing rainwater to overflow from the A-pillar and drip directly onto the Body Control Module (BCM) and its connectors, located in the passenger-side footwell. This specific failure pattern is a very common cause of code U1002 and a host of bizarre electrical issues on this vehicle, as documented extensively in owner forums.

Diagnostic Flowchart

Tap your situation to follow the diagnostic path that matches what you're seeing on this vehicle.

Generation note: This range covers the end of the V35 generation (2005-2006 Sedan, 2005-2007 Coupe) and the start of the V36 generation (2007-2008 Sedan, 2008 Coupe). While the underlying cause is often similar, the infamous sunroof drain leak causing BCM failure is a well-documented problem on the V36 chassis. The V35 chassis is also prone to water intrusion in the IPDM area near the battery due to clogged cowl drains.

Symptoms You May Notice

• Multiple warning lights on the dashboard (VDC OFF, SLIP, ABS, Service Engine Soon)
• Vehicle will not start or has an intermittent no-crank condition.
🎬 Watch: Troubleshooting a no-crank, no-start condition on a G35.
• Engine stalls while driving.
• Transmission is stuck in a single gear or shifts erratically.
• Intelligent Key (I-Key) not detected or only works in the slot.
• Gauges, radio, or climate control stop working or behave erratically.
• Clicking noises from the dash or door locks.
• Trunk opens by itself randomly.
• OBD-II scanner fails to connect or power on.

Most Likely Causes

1. Water Intrusion on Body Control Module (BCM) 🔴 High Probability → Shop Body Control Module The front sunroof drain tubes are known to clog with debris. The design allows overflowing water to run down the passenger A-pillar and drip directly onto the BCM and its wiring harnesses.
   How to confirm: Check for dampness or standing water in the passenger-side footwell carpet. Remove the passenger kick panel and glove box to visually inspect the BCM (a white box with multiple connectors) for signs of moisture, water stains, or blue/green corrosion on the pins and connectors.
   Typical fix: First, clear the clogged sunroof drains using compressed air or a flexible wire like weed trimmer line. The BCM and its connectors must be disconnected (with the battery unplugged), thoroughly dried, and cleaned of any corrosion with electronics cleaner. If the module is internally damaged, it will require replacement and reprogramming by a dealer or qualified shop. Some owners have successfully rerouted the drain tube to bypass the firewall grommet entirely 🎬 See this walkthrough on cleaning and repairing sunroof drains. as a permanent fix.
   Est. part cost: $500-$800
2. Low Battery Voltage or Failing Battery 🔴 High Probability → Shop Vehicle Battery Infiniti's diagnostic guidelines explicitly state that low battery voltage (below 10V) can set CAN DTCs. As a battery ages, its voltage can drop enough under load (especially during cranking) to cause modules to temporarily fall off the communication network, triggering a U1002 code.
   How to confirm: Test the battery with a multimeter. A healthy battery should read above 12.4V with the engine off. Perform a load test at an auto parts store for a definitive diagnosis. Check that the alternator is charging between 13.5V-14.8V with the engine running.
   Typical fix: Replace the battery. Ensure the new battery meets or exceeds the OEM specifications for Cold Cranking Amps (CCA). After replacement, perform an ECU reset procedure.
   Est. part cost: $150-$300
3. Corroded or Loose Ground Wires 🟡 Medium Probability The main battery-to-chassis ground cable and various engine block grounds can corrode over time, creating high resistance and causing intermittent electrical problems that disrupt CAN communication.
   How to confirm: Visually inspect the negative battery cable and its connection point to the car's body for corrosion or looseness. Locate and inspect other key grounding points on the engine block, plenum, and near the ECM. A resistance check between the ground point and the negative battery terminal should read less than 1 ohm.
   Typical fix: Disconnect, clean all contact points with a wire brush until they are shiny, and securely retighten the ground connections. Apply dielectric grease to prevent future corrosion. If the cable itself is heavily corroded, replace it. The OEM negative battery cable for the V35 is part number 24080-AM600. 🎬 Watch: How to install a grounding kit on your G35. Aftermarket splice kits are also available.
   Est. part cost: $20-$60

Rare But Worth Checking

• Failing ABS Actuator/Control Unit: The ABS unit is a critical node on the CAN network. If it fails internally, it can disrupt all communication, causing a U1002 code in other modules. In some cases, the ABS actuator can leak brake fluid internally, causing an electrical short that can, in rare instances, lead to a fire. Diagnosis requires an advanced scan tool to see if the ABS module is unresponsive.
• Faulty IPDM (Intelligent Power Distribution Module): The IPDM, located in the battery compartment, is another key module on the network. It can also be susceptible to water damage from clogged cowl drains, leading to network failures.
• Poorly Installed Aftermarket Electronics: Improperly tapped wires for aftermarket stereos, alarms, or remote starters can interfere with the CAN bus signals and cause communication codes. The CAN wires are a twisted pair.

Diagnosis Steps

1. Check for Water Intrusion: Pull back the passenger-side carpet and check for any signs of moisture. This is the most common cause on this platform. Also check the battery compartment for water near the IPDM.
2. Test Battery and Charging System: Ensure the battery voltage is above 12.4V (engine off) and that the alternator is charging correctly (13.5V-14.8V engine on). A weak battery is a primary cause of communication codes.
3. Inspect All Grounds: Disconnect the negative battery terminal. Inspect the main battery ground cable connection to the chassis for corrosion. Clean and tighten it regardless of appearance. Inspect other major ground points on the engine and near affected modules.
4. Check Fuses: Inspect fuses related to the BCM, ECM, and other control modules, particularly in the IPDM next to the battery and the fuse block in the driver's kick panel.
5. Perform a CAN System Check (Professional): Use an advanced scan tool (like Infiniti CONSULT) to perform a 'CAN Diagnosis Support Monitor'. This will show which specific modules are not communicating, pinpointing the source of the network failure.
6. Measure CAN Resistance: With the battery disconnected, a technician can measure the resistance across the CAN-H (Pin 6) and CAN-L (Pin 14) pins at the OBD-II port. A healthy network should read approximately 60 ohms. A reading of 120 ohms indicates a problem with a terminating resistor or a break in the wiring. A reading near 0 ohms indicates a short between the CAN lines.
7. Isolate Modules: If a specific module is suspected (e.g., the ABS unit or a water-damaged BCM), a technician may disconnect it from the network to see if communication is restored to the other modules and if the CAN resistance returns to 60 ohms.

Parts You'll Likely Need

• Body Control Module (BCM) (OEM #284B1-JK62A (2007-2008 G35), 284B1-CM32A (2005-2006 G35)) — This module is frequently damaged by water from clogged sunroof drains, a very common issue on the G35. It must be replaced or repaired if corroded. Replacement requires programming to the vehicle's keys and options.
  Trusted brands: Infiniti (OEM), Module Mechanics (Remanufactured), Circuit Board Medics (Repair Service)
  OEM price range: $500-$800
  Aftermarket price range: $200-$400 (Used/Remanufactured/Repair Service)
• Battery — Low system voltage from a weak or failing battery is a very common trigger for network communication codes.
  Trusted brands: Interstate, DieHard, Duralast
  OEM price range: $200-$350
  Aftermarket price range: $150-$300
• Grounding Wires/Kit — Corroded or high-resistance ground connections are a common cause of intermittent electrical faults and CAN codes. Cleaning original grounds or adding a supplementary kit can improve electrical stability.
  Trusted brands: Stillen, Z1 Motorsports, DIY (using 4-8 gauge wire)
  OEM price range: $20-$60 (OEM Cable)
  Aftermarket price range: $30-$150 (Aftermarket Kit)

Related Codes That Often Appear With This One

• U1000 — U1000 is the general CAN communication failure code. U1002 is a more specific and sensitive version, and they often appear together.
• U1001 — This code specifically points to a communication loss with the ECM. It often accompanies other CAN codes when the network is unstable.
• C1109 — This code indicates a power supply issue (low voltage) to the ABS actuator. It can be triggered by a failing battery or alternator, which in turn can cause network codes like U1002.

Technical Service Bulletins (TSBs) & Recalls

• ITB10029A / NTB10-066B: Provides general diagnostic guidelines for CAN codes U1000, U1001, U1002, emphasizing checking battery voltage and using the CONSULT tool.
• NTB13-076B: Provides a diagnostic flow chart for CAN communication issues on 2005-2013 Nissan/Infiniti vehicles.

Platform-Specific Known Issues

• Sunroof Drain to BCM Leak (V36 Chassis): The 2007-2008 G35 Sedans are particularly known for the front sunroof drain tubes clogging or the firewall grommet failing. This causes water to run down the passenger A-pillar and directly onto the BCM, leading to corrosion and CAN network failure (U1002). The first sign is often the Intelligent Key system failing, followed by a no-start condition.
• Cowl Drain to IPDM Leak (V35 Chassis): On the earlier 2005-2006 models, drains in the cowl area below the windshield can clog with leaves and debris. This can cause the battery compartment to fill with water, submerging and damaging the Intelligent Power Distribution Module (IPDM), which is a critical CAN network module.

Mechanic-Grade Diagnostic Values

• CAN Bus Resistance — expected: Approximately 60 Ω. Failure: A reading of ~120 Ω indicates an open circuit or a missing terminating resistor. A reading near 0 Ω indicates a short between the CAN H and CAN L wires.
• Terminating Module Resistance — expected: Approximately 120 Ω. Failure: A reading significantly different from 120 Ω suggests the module's internal terminating resistor has failed.

Scan Tool Commands That Help

• Infiniti CONSULT-III Plus: CAN Diagnosis Support Monitor — This is the primary function to use when diagnosing U1002. It polls all modules on the network and displays a matrix showing which modules are failing to communicate, quickly identifying the source of the network disruption.
• Infiniti CONSULT-III Plus: ECU Programming / Configuration — This function is required after replacing a control module like the BCM. The new module must be programmed to the vehicle's VIN and configuration to restore communication and functionality with the Intelligent Key and other systems.

Wiring & Ground Locations

• BCM Connectors — Behind the passenger-side kick panel and glove box. It is a white box with several large multi-pin connectors.. This is the most common point of failure due to water intrusion from clogged sunroof drains. Corrosion on these connectors or internal damage to the BCM will sever CAN communication.
• IPDM E/R (Intelligent Power Distribution Module Engine Room) — In the engine compartment, next to the battery, under a plastic cover.. The IPDM is a terminating module on the CAN bus and also controls power to many other modules. Water intrusion from clogged cowl drains or internal failure can cause network-wide issues.
• Primary Transmission Ground — Located on the top middle of the timing chain cover. Two wires are landed here, one of which is the transmission ground.. A poor ground for the transmission can cause erratic shifting and communication issues with the TCM, which can broadcast errors on the CAN bus.
• Main Chassis Grounds — Key locations include the negative battery cable connection to the chassis, and ground points designated M30 and M66, which are located behind the instrument cluster and right-side of the dash, respectively.. High resistance at any of these main grounding points can cause voltage drops that lead to random module communication failures and U-codes.

Real Owner Repair Stories

• G35Driver Forum User (2008 Infiniti G35x) — Car would not start, no response from push-button ignition, keyless entry not working, but brake lights and interior lights functioned. Convinced it was a BCM issue due to known water leak problems.
  ❌ Tried (didn't work) Replacing the battery in the key fob.
  ✅ What actually fixed it The user corrected a sunroof drainage issue and thoroughly dried the car's interior. Although the symptoms pointed directly to a wet BCM, the user did not explicitly state they replaced the BCM, but implied the water leak was the root cause of the electronic failures.
• MyG37 Forum User (2009 G37x (similar platform)) — Sluggish automatic transmission shifts, laggy throttle response.
  ❌ Tried (didn't work) ECU tune did not fully resolve the issue.
  ✅ What actually fixed it The user created and installed a DIY grounding kit. They reported that after installation, nearly all of the transmission shifting delay was fixed, suggesting that poor grounding was a contributing factor to the electronic performance issues.

OEM Part Supersession History

• 284B1-JK61A → 284B1-JK62A — Part revision by the manufacturer.
  Heads up: Part 284B1-JK61A was used for the early 2007 G35 Sedan production (up to 07/2007). It was replaced by 284B1-JK62A, which was used from 07/2007 to 08/2008. While they may be physically interchangeable, using the wrong revision can cause compatibility issues. Always match the part number from the original BCM.

Model Year Variations Within This Range

• 2005-2006 (V35 Chassis): The BCM is located behind the left kick panel. While still susceptible to electrical issues, the specific failure pattern of the sunroof drain leaking directly onto the BCM is less common than on the V36. V35s are more known for water pooling in the battery compartment, affecting the IPDM.
• 2007-2008 (V36 Chassis): The BCM is located behind the passenger kick panel/glove box, directly in the path of water from the notoriously failure-prone sunroof drain grommet. The engine was updated from the VQ35DE to the VQ35HR in 2007, which involved significant electronic and wiring changes.