U1500 on 2000-2007 Chevrolet Impala: OnStar Module Fault and Battery Drain Fixes

What's Unique About the 2000-2007 Chevrolet IMPALA

For this generation of Impala and its platform mates, the U1500 code is deeply tied to the history of the OnStar system. Many of these vehicles were equipped with analog-only (pre-2008) or 2G (2014 and older) cellular modules. When cellular carriers began shutting down their analog networks around 2008 and 2G networks by 2022, these modules could no longer connect. This often caused the module to continuously search for a signal it could never find, leading to internal faults, a parasitic battery drain that could kill a battery in days, and the U1500 trouble code. This makes the problem less about a defective part and more about technological obsolescence.

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 eighth generation (2000-2005) and the start of the ninth generation (2006-2007) Impala. The OnStar module issue is common to both generations, as the underlying analog and early digital cellular technology became obsolete. The fuse and module locations differ between generations. For 8th gen (2000-2005), fuse boxes are on both the driver's and passenger's side of the dash. For 9th gen (2006-2007), the main fuse box is under the hood, with another in the passenger footwell.

Symptoms You May Notice

• Parasitic battery drain leading to a dead battery, sometimes overnight or within a few days.
• Red or flashing OnStar status light on the rearview mirror.
• "Phone Unavailable" or similar audio message from the system, sometimes repeating.
• Inability to connect to OnStar services.
• "Battery Saver Active" message appearing on the driver information center.
• Green OnStar light may remain on even when the vehicle is off.

Most Likely Causes

1. Internal Failure of the OnStar/VCIM Module 🔴 High Probability As documented in GM Technical Service Bulletins like PIC3278G and PIC3718E, the VCIM in these vehicles is prone to internal faults that trigger code U1500. This can be due to age or, more commonly, the module's constant, failed attempts to connect to a defunct analog or 2G network, causing it to never enter its low-power 'sleep' mode.
   How to confirm: Perform a parasitic draw test. A normal draw after all modules go to sleep (wait at least 20-30 minutes) should be under 50mA (0.05A). A faulty OnStar module can cause a draw of several hundred milliamps to over 2 amps. If a significant draw is found, pull the OnStar/VCIM fuse. If the draw drops to a normal level, the module is confirmed as the cause.
   Typical fix: The most common and practical fix is to permanently disable the module by leaving the fuse out or unplugging the module directly. This resolves the battery drain with no negative effects on vehicle operation.
   Est. part cost: $0
2. Obsolete Analog/2G OnStar Module 🔴 High Probability Vehicles in this year range were manufactured before the mandatory switch to modern digital cellular networks for OnStar. The analog network was shut down around 2008, and the 2G network was decommissioned by the end of 2022, rendering the hardware in these cars useless.
   How to confirm: This is inherent to the vehicle's age. If the OnStar system hasn't been physically upgraded to a modern digital unit (a rare and expensive service), it is obsolete. The presence of U1500 combined with a battery drain is strong evidence. GM explicitly states in bulletins not to replace the module for this reason, as the new part would also be unable to connect.
   Typical fix: Disconnect the module by pulling the fuse to prevent battery drain. Upgrading to a modern system is not practical or cost-effective for these vehicles.
   Est. part cost: $0

Diagnosis Steps

1. Read the trouble codes with an OBD-II scanner to confirm U1500 is present.
2. Observe the OnStar light on the rearview mirror. A red light indicates a system fault.
3. Perform a parasitic draw test. Connect a multimeter set to measure Amps (use the 10A setting) in series with the negative battery terminal. Wait at least 20-30 minutes for all vehicle modules to enter sleep mode.
4. A normal draw should be under 50mA (0.05A). A draw from a faulty OnStar module is often significantly higher, from 200mA to over 2A.
5. Locate the fuse for the OnStar module (VCIM). On 9th-gen Impalas (2006-2007), this is the 10A red fuse labeled 'ONSTAR' in the under-hood fuse box on the passenger side. On 8th-gen Impalas (2000-2005), check the fuse panels on both the driver's and passenger's side of the dashboard for a fuse labeled 'ONSTAR' or 'INFO'.
6. Pull the OnStar fuse and watch the multimeter. If the parasitic draw drops to a normal level (e.g., from 1.5A to 0.03A), you have confirmed the OnStar module is the cause.
7. The simplest and most effective fix is to leave the fuse removed. This will disable OnStar but resolve the battery drain and clear the U1500 code.
8. Alternatively, you can unplug the VCIM module itself. It is often located behind the glove box or in the trunk.

Parts You'll Likely Need

• No parts needed (fuse removal) — The most common and effective solution is to simply disable the faulty/obsolete module by pulling its fuse, which resolves the battery drain at no cost.
  OEM price range: $0
  Aftermarket price range: $0
• Vehicle Communication Interface Module (VCIM) (OEM #15810816) — If you wish to replace the module, this is a common part number for the 2006-2007 era. However, replacement is not recommended as the service is obsolete and the new part will also be unable to connect to a network, offering no benefit. Used modules are available but serve little purpose.
  Trusted brands: ACDelco, Motorola (Original Manufacturer)
  OEM price range: $200-$400 (if available)
  Aftermarket price range: $30-$100 (used)

Related Codes That Often Appear With This One

• B1000 — GM Technical Service Bulletins PIC3278F and PIC3278G explicitly state that an internal OnStar module fault can set either U1500 or B1000. These codes are often seen together for this issue.

Technical Service Bulletins (TSBs) & Recalls

• PIC3278F / PIC3278G: Notes that an internal fault in the OnStar module can produce a 'Phone Unavailable' audio message and set a U1500 or B1000 DTC.
• PIC3718E: Addresses a 'no power or no connect concern' with a red OnStar LED and DTC U1500, recommending replacement of the VCIM for specific STID number ranges on Gen6 OnStar systems.
• GM Bulletin 14648: Addresses a similar battery drain issue on 2008-2010 GM vehicles where the green OnStar light stays on. The official fix is to remove the OnStar fuse to reset it, acknowledging the module as the cause of the drain.

Platform-Specific Known Issues

• The primary issue is the obsolescence of the factory-installed analog (Gen 6 and older) OnStar module. After the analog and 2G cellular networks were decommissioned, these modules became a common source of parasitic battery drain as they perpetually searched for a non-existent signal.
• Technical Service Bulletin #PIC3718E notes that certain vehicles with Gen6 VCIMs having Station Identification Numbers (STID) in the ranges of 14,000,000-16,000,000 or 22,000,000-23,200,000 were particularly prone to a 'no power or no connect concern' with a red LED and DTC U1500, requiring module replacement at the time.

Mechanic-Grade Diagnostic Values

• Parasitic Draw (Sleep Mode) — expected: Less than 50mA (0.050A). Failure: A draw of several hundred milliamps to over 2A often points to a faulty OnStar module that is not entering sleep mode.
• GM Class 2 Serial Data Bus Voltage — expected: The bus is active at a nominal 7.0 volts and inactive at ground potential. It toggles between these states to transmit data.. Failure: A bus that is stuck high (e.g., over 10V) or shorted to ground indicates a fault on the data line, potentially caused by a malfunctioning module like the VCIM or EBCM.
• Operating Voltage for VCIM — expected: Between 9.5 and 15.5 volts.. Failure: The module may not operate correctly or set codes if the supply voltage is outside this range.

Scan Tool Commands That Help

• GM Tech 2 / SPS: OnStar Activation (ONSA) / VCIM Vehicle Communication Interface Module Set-up — This function is required after replacing a VCIM on 2008 and prior model year vehicles. It gathers critical information from the new module and sends it to OnStar to activate the unit for the specific vehicle and subscriber account. Failure to perform this setup will result in an inoperative system.

Wiring & Ground Locations

• VCIM (2006-2007) — Mounted to the rear of the left rear wheelhouse, accessible by pulling back the rear compartment/trunk trim panel.. This is the physical location of the module that sets the U1500 code. Access is required to disconnect it as an alternative to pulling the fuse.
• VCIM (2000-2005) — Located in the trunk, on the back of the rear seat framing, typically on the right (passenger) side.. This is the location of the module for the 8th generation Impala. Access is needed to physically unplug the unit.
• BCM (Body Control Module) — To the left of the steering column, accessible after removing the lower dash insulator panel.. The BCM acts as a gateway for communication between various modules. While not the direct cause of U1500, its ground points and connectors are relevant for any deeper network diagnostics.
• G301 / G302 — G301 is below the driver's door opening, rear of the left 'A' pillar. G302 is in the corresponding location on the passenger side.. These are primary body ground points. A poor ground here could potentially affect modules on the Class 2 data bus, although U1500 is almost always an internal VCIM fault.
• Class 2 Serial Data Splice Pack (SP206 / SP207) — Located on the instrument panel harness, near the steering column.. This is where the Class 2 data wires from multiple modules join together. In advanced diagnostics, a technician can isolate individual modules from the bus at this point to find one that may be corrupting the network.

OEM Part Supersession History

• 15098277 → N/A — Part for early generation.
  Heads up: This part number is listed for 2000-2004 Impalas.
• 25749851 → N/A — Part for mid-generation.
  Heads up: This part number is listed for 2004 Impalas.
• 15832272 → 15810816 (mentioned in pass 2) — Part for later generation.
  Heads up: Part number 15832272 is specified for 2006 Impalas. It's crucial to match the part number as module hardware and software changed. Never swap VCIMs between vehicles as they are tied to the VIN.

Model Year Variations Within This Range

• 2000-2005 (8th Gen): The VCIM is typically located in the trunk, mounted to the rear seat frame structure. The primary fuse boxes are located on the driver's and passenger's sides of the instrument panel.
• 2006-2007 (9th Gen): The VCIM is located in the trunk, mounted to the left rear wheelhouse. The primary fuse box containing the OnStar fuse is located under the hood on the passenger side.