U1002 on 2008-2012 Infiniti EX35: CAN Communication Failure Causes and Fixes

What's Unique About the 2008-2012 Infiniti EX35

The Infiniti EX35 shares its platform and many electronic systems with the G37, making it susceptible to similar issues. A widely documented problem on this platform is water intrusion from clogged sunroof drains. The drain tubes, particularly the one on the passenger side, can clog or the firewall grommet can shrink, causing water to overflow and drip directly onto the Body Control Module (BCM) and its connectors in the passenger-side footwell. This specific water leak issue is a primary suspect and should be investigated before extensive electrical diagnosis, as confirmed by numerous owner experiences on forums.

Diagnostic Flowchart

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

Symptoms You May Notice

• Check Engine Light is on
• ABS, VDC, and/or SLIP warning lights are illuminated
• Vehicle may not start with the push-button ignition, but may start with the remote starter
• Erratic or harsh transmission shifting
• Gauges on the instrument cluster may behave erratically or not work
• Loss of power windows, locks, or other body functions
• Car alarm going off randomly
• Radio or infotainment screen stays on after the car is turned off
• Inability to shut the engine off with the push button

Most Likely Causes

1. Water Damage to Body Control Module (BCM) 🔴 High Probability → Shop Body Control Module The EX35, like the related G37, has sunroof drains that are notorious for clogging or having their firewall grommets shrink and fail. When they do, water overflows and drips into the passenger footwell, directly onto the BCM and its connectors, causing corrosion and short circuits. This is the most frequently cited cause in owner forums.
   How to confirm: Check for dampness, water stains, or a musty smell in the passenger-side footwell carpet and under the glove box. Remove the passenger kick panel to visually inspect the BCM 🎬 See this walkthrough on locating and removing the BCM. (a white or black plastic box with multiple large connectors) and its wiring harness for green or white corrosion.
   Typical fix: The BCM must be removed, dried, and its connectors cleaned with electrical contact cleaner. If corrosion is severe, the BCM and/or connector pigtails may need replacement. A replacement BCM requires programming by a dealer or a specialized shop. Crucially, the sunroof drains must be cleared or modified to prevent recurrence. Some owners perform a 'forever fix' by rerouting the drain to bypass the problematic firewall grommet entirely.
   Est. part cost: $50-$800
2. Low Battery Voltage or Poor Ground Connections 🔴 High Probability → Shop Vehicle Battery Modern vehicles with numerous control modules are highly sensitive to system voltage. A weak battery or corroded main ground straps can cause modules to drop off the network intermittently, especially during engine cranking. This is a common issue on aging Nissan/Infiniti platforms.
   How to confirm: Test the battery voltage with a multimeter (should be >12.4V with engine off). Load test the battery, as a battery can show good voltage but fail under load. Inspect the main battery ground cable (negative terminal to chassis) and other major chassis ground points in the engine bay for looseness and corrosion (green/white powder).
   Typical fix: Charge or replace the battery. Disconnect, clean with a wire brush, and securely re-tighten all major ground connections. Applying dielectric grease can prevent future corrosion.
   Est. part cost: $5-$250
3. Damaged CAN Wiring Harness 🟡 Medium Probability Wiring can be damaged from chafing against chassis components, previous improper repairs, or rodent damage. The main harness grommet at the firewall can also be a source of water leaks that corrode wires.
   How to confirm: This requires a visual inspection of the wiring harness between major control modules (ECM, TCM, BCM, ABS). A professional would use a multimeter to check for ~60 ohms of resistance across the CAN-H (Pin 6) and CAN-L (Pin 14) at the DLC with the battery disconnected. A reading of 120 ohms suggests a break in the circuit or a problem with a terminating resistor. A reading near 0 ohms indicates a short circuit.
   Typical fix: Repair the broken or shorted section of the CAN wiring harness. This may involve soldering, heat-shrinking, and re-looming the affected wires.
   Est. part cost: $10-$100
4. Failing ABS Actuator / Control Unit ⚪ Low Probability The ABS module is a critical node on the CAN network. Internal failure of this module, sometimes due to voltage spikes or internal corrosion, can disrupt communication across the entire system.
   How to confirm: This is a difficult diagnosis. An advanced scan tool (like Infiniti CONSULT) may show the ABS module is not responding ('NG' status on CAN Diagnosis Support Monitor). A technician may disconnect the ABS module to see if communication between other modules is restored. A visual inspection of the module's connector for corrosion is also necessary.
   Typical fix: Replace the ABS actuator and control unit assembly, followed by a brake fluid bleed and system calibration, which often requires a specialized scan tool.
   Est. part cost: $1000-$1800

Diagnosis Steps

1. Check Battery Health: Verify battery voltage is above 12.4V and have it professionally load tested. A weak battery is a very common and simple-to-fix cause of network codes.
2. Inspect for Water Intrusion: This is a critical step for the EX35. Pull back the passenger-side carpet and remove the plastic kick panel. Feel the carpet padding and insulation for any signs of moisture. Visually inspect the Body Control Module (BCM) and its connectors for water stains or green/white corrosion.
3. Clear Sunroof Drains: Regardless of finding water, proactively clean the sunroof drains. 🎬 Watch: How to clean your sunroof drains before they clog. Use a flexible drain cleaning tool or compressed air to clear the front drains. Many owners recommend modifying the drain ends at the firewall to prevent future clogs.
4. Check Grounds: Inspect the main battery-to-chassis ground strap and other major engine/chassis ground points for tightness and corrosion. Clean and tighten as necessary.
5. Perform CAN System Diagnosis: Use an Infiniti-compatible advanced scan tool to run a 'CAN Diagnosis Support Monitor'. This will show which modules are online ('OK') and which are not communicating ('NG'). This is the most effective way to narrow down the source of the problem.
6. Check CAN Bus Resistance: Disconnect the battery. Use a multimeter to measure the resistance between Pin 6 (CAN-H) and Pin 14 (CAN-L) at the OBD-II port. 🎬 Watch: How to perform a CAN bus multimeter check. A healthy network should read approximately 60 ohms. A reading of 120 ohms suggests a break in the circuit or a faulty terminating module. A reading near 0 ohms indicates a short circuit between the CAN wires.
7. Isolate Modules: If the resistance is incorrect, a technician will disconnect modules one by one from the network (starting with the one showing 'NG' on the scan tool) until the resistance returns to normal, thereby identifying the faulty module or wiring section.

Parts You'll Likely Need

• Body Control Module (BCM) (OEM #284B1-1CA9C (supersedes 284B1-1BA0A, 284B1-1CA4C, and others; always verify by VIN)) — Frequently fails due to water damage from clogged sunroof drains on this platform. A replacement requires programming.

Related Codes That Often Appear With This One

• U1000 — U1000 is a general CAN communication failure code. U1002 is a more specific version with stricter detection criteria, and they often appear together as they indicate the same underlying network instability.
• U1001 — This code specifically points to a communication loss with the ECM. It often accompanies other CAN codes when the network is unstable.
• U0121 — This code indicates a lost communication with the ABS control module. It can be set alongside U1002 if the ABS module is the source of the network disruption.
• C1109 — This code points to a power supply issue (low voltage) at the ABS actuator. It can be a clue that a weak battery or bad ground is the root cause of the network failure triggering U1002.

Technical Service Bulletins (TSBs) & Recalls

• ITB10-029A: 'CAN COMMUNICATION CODES – DIAGNOSTIC TIPS & GUIDELINES' - Explains that U1002 is a communication code with a tighter specification than U1000 and provides diagnostic procedures for all 2005-2015 Infiniti vehicles.

Platform-Specific Known Issues

• Clogged sunroof drains are a well-known issue that leads to water leaking into the cabin, specifically onto the BCM located in the passenger kick panel area, causing widespread electrical and network problems. YouTube videos show detailed procedures for cleaning and modifying these drains.
• A 'forever fix' popular in online communities involves rerouting the sunroof drain tubes to the A/C drain line, completely bypassing the firewall grommet that is prone to failure.
• The design of the sunroof drain ends includes a small shield to prevent insects from entering, but this shield also easily traps small debris, leading to clogs. Many owners snip this shield off as a preventative measure.

Mechanic-Grade Diagnostic Values

• CAN Bus Resistance — expected: ~60 Ω. Failure: A reading of ~120 Ω indicates a missing terminating resistor or an open circuit. A reading near 0 Ω indicates a short between the CAN High and Low lines. A reading of ~40-45 Ω may indicate a third, unintended resistor on the network or a failing module.
• CAN Bus Voltage (Key On, Engine Off) — expected: CAN-H (Pin 6 to Ground): ~2.5V to 3.0V. CAN-L (Pin 14 to Ground): ~2.5V to 2.0V.. Failure: Voltages that are stuck high, low, or at 0V indicate a short to power or ground on the respective line. These are best measured with an oscilloscope but a multimeter can spot hard faults.
• Ground Point Voltage Drop — expected: < 0.2 Volts. Failure: A reading higher than 0.2V indicates high resistance in the ground connection, which can cause modules to malfunction.

Scan Tool Commands That Help

• Infiniti CONSULT-II / CONSULT-III Plus: CAN Diagnosis Support Monitor — This is the primary and most crucial first step when diagnosing any 'U' code. It polls all modules on the CAN network and provides a simple 'OK' or 'NG' (No Good) status for each one, immediately showing the technician which module is offline and requires investigation.
• Infiniti CONSULT-II / CONSULT-III Plus: Self-Diagnostic Results — After identifying a non-communicating module with the CAN Diagnosis Support Monitor, this function is used to retrieve DTCs from all the *other* modules. This helps build a complete picture of the fault, as multiple modules may log codes related to the primary failure.
• Infiniti CONSULT-II / CONSULT-III Plus: ECU Programming / Configuration — This function is mandatory after replacing a major control module like the BCM. The new module must be programmed with the vehicle's VIN and specific configuration data to allow it to communicate on the network and function correctly.

Wiring & Ground Locations

• BCM (Body Control Module) — Located in the passenger kick panel area, typically behind a plastic trim piece to the right of the passenger's feet.. This is the module most susceptible to water damage from clogged sunroof drains, a primary cause of U1002 on this platform. Its connectors carry CAN bus signals.
• CAN Bus Wires at BCM — In the main BCM connector (a large, multi-pin connector), the CAN-H wire is typically Blue and CAN-L is Pink. Specifically, on the black 40-pin connector, CAN-L is Pin 19 and CAN-H is Pin 20.. These are the specific pins to inspect for corrosion if water intrusion is suspected at the BCM. They can also be used as a test point for CAN signals if the DLC is inaccessible.
• Ground Points B202 / B224 — Ground B202 is located in the right kick panel area. Ground B224 is located in the right 'C' pillar.. These are chassis ground points for various components, including the BCM and other nearby modules. Corrosion or looseness at these points can disrupt module communication.
• IPDM E/R (Intelligent Power Distribution Module Engine Room) — This is the 'smart' fuse and relay box located in the right-rear of the engine compartment.. The IPDM is a terminating module for the CAN bus and controls power to many other modules. A failure within the IPDM can bring down the entire network.

Real Owner Repair Stories

• YouTube Channel 'How2Helen' (2011 Infiniti EX35) — Interior water leak, damp A-pillar cover, wet passenger floorboard. While not explicitly stating a U1002 code, these are the direct precursor symptoms to the BCM failure that causes it.
  ❌ Tried (didn't work) Initial inspection focused only on the sunroof opening itself.
  ✅ What actually fixed it The sunroof drain hose had become detached from the sunroof assembly due to being clogged at the firewall exit point. The fix involved dropping the headliner to reattach the hose, then accessing the drain end at the firewall and snipping off the restrictive anti-insect shield to allow debris to pass through freely, preventing future clogs.
• YouTube Channel 'How to Helen' (2008 Infiniti EX35) — Proactive maintenance to prevent the common water leak issue. The video shows the passenger side drain end is already becoming 'gunked up'.
  ✅ What actually fixed it The owner performed preventative maintenance by accessing the sunroof drain ends at the firewall on both the driver and passenger sides. The small plastic 'protective shield' inside the rubber drain tip, which is designed to keep insects out but is prone to clogging with dirt and debris, was clipped out. This modification allows water and small debris to flow through without obstruction.

OEM Part Supersession History

• 284B1-1BA0A, 284B1-1BM0A, 284B1-1CA0A, 284B1-1CA0B, 284B1-1CA0C, 284B1-1CA4C, 284B1-1CA5C, 284B1-1CA7C → 284B1-1CA9C — Standard part revisions for bug fixes, component updates, or manufacturing process changes.
  Heads up: While many numbers are superseded, it is critical to match the part number on the original BCM or verify by VIN. A BCM from a vehicle with different options (e.g., AWD vs RWD, Tech Package) may not program or function correctly even if it physically fits.

Model Year Variations Within This Range

• 2011-2012: For the 2011 model year, the EX35's 5-speed automatic transmission was replaced with a new 7-speed automatic transmission. Standard wheel size also increased from 17 to 18 inches. This change affects the TCM and its communication on the CAN bus, though the U1002 diagnostic process remains the same.
• 2008: The 2008 model was the launch year and had a 5-speed automatic transmission. Some features that became standard in later years, like leather seating and a RearView Monitor, were optional.