U0100 on 2018-2023 Volvo S90: Lost Communication With ECM Causes and Fixes

What's Unique About the 2018-2023 Volvo S90

The Volvo S90, built on the SPA (Scalable Product Architecture) platform, has a highly complex and sensitive electrical network. Unlike older vehicles, a U0100 code here is frequently traced back to two specific areas: general battery health and the Vehicle Connectivity Module (VCM). These modern Volvos are extremely sensitive to low voltage, and a slightly weak 12V battery can trigger a cascade of communication faults. Additionally, the VCM, which manages telematics and acts as a network gateway, has its own small backup battery that is a known failure point, causing network errors and battery drain. This issue is common enough that Volvo has issued Technical Journals (e.g., TJ 36916.1.0 and 36916.2.0) regarding its replacement.

Symptoms You May Notice

• Engine will not start (no-crank or cranks but won't fire)
• Check Engine Light is on
• Multiple other warning lights may illuminate simultaneously (e.g., ABS, SRS, Transmission)
• Vehicle enters 'limp mode' or 'turtle mode' with severely reduced power
• Instrument cluster gauges may stop working or go blank
• Engine may stall intermittently while driving
• "Volvo On Call Service Required" message may appear if the VCM backup battery is the cause
• Audio/navigation system fails or reboots intermittently

Most Likely Causes

1. Weak or Failing 12V Main Battery 🔴 High Probability Modern Volvos have a high constant electrical draw and are extremely sensitive to voltage drops. A battery that is even slightly degraded can fail to provide the stable voltage required by the network modules during startup, triggering communication faults.
   How to confirm: Use a digital multimeter to test the battery voltage with the car off. A healthy battery should read at least 12.4-12.6 volts. Anything below 12.0V indicates a discharged state that can cause network issues. Have the battery load-tested at an auto parts store to confirm its health under load.
   Typical fix: Replace the main 12V AGM battery (typically Group Size H8). 🎬 Watch: How to replace the auxiliary and support batteries. The new battery must be registered with the vehicle's Battery Management System (BMS) using a capable scan tool like VIDA to ensure proper charging and longevity.
   Est. part cost: $250-$450
2. Failed VCM (Vehicle Connectivity Module) Backup Battery 🔴 High Probability The small lithium-ion battery that powers the VCM for the 'Volvo On Call' emergency system has a finite lifespan (typically 3-5 years). When it fails, it can cause network communication errors, a persistent 'Volvo on Call Service Required' message, and DTC VCM-U105000. Volvo has issued multiple service actions and technical journals (like TJ 36916.1.0 and 36916.2.0) for this issue.
   How to confirm: The primary symptom is the 'Volvo On Call Service Required' message on the driver display. A Volvo-specific scan tool can directly query the VCM for faults related to its internal battery, such as VCM-U105000.
   Typical fix: Replace the VCM backup battery (Part No. 31450445 or superseding part 32279613). On the S90, this module is located behind the right-side trunk trim panel. 🎬 See this walkthrough for VCM backup battery removal and installation. After replacement, a dealer or specialist must use VIDA to perform a software download to clear the stored fault code and restore function.
   Est. part cost: $50-$100
3. CAN Bus Wiring or Connector Issue 🟡 Medium Probability The CAN bus is a network of twisted-pair wires running throughout the vehicle. A loose connector, corroded pin, or chafed wire can disrupt the entire network.
   How to confirm: This requires a visual inspection of major network harnesses and connectors, particularly at the ECM and CEM. A technician would use a multimeter to check for 60 ohms of resistance across pins 6 and 14 of the OBD-II port (with the battery disconnected) to verify the integrity of the network's terminating resistors. A reading of 120 Ohms suggests a break in the circuit or a faulty module.
   Typical fix: Repair the damaged section of wiring or clean/replace the corroded connector. This is labor-intensive and requires wiring diagrams to trace the fault.
   Est. part cost: $10-$50
4. Faulty Central Electronic Module (CEM) ⚪ Low Probability The CEM acts as a primary gateway and fuse box for many of the vehicle's networks. While more common on the older P3 platform, a CEM failure on the SPA platform can still cause a total network collapse, often due to internal software glitches or hardware failure.
   How to confirm: Diagnosis involves checking for power and ground at the CEM and using a Volvo-specific scan tool to see if the module is communicating. This is typically diagnosed by a process of elimination after ruling out battery and wiring issues.
   Typical fix: Replace and program the Central Electronic Module. This requires dealer-level software (VIDA) for programming and configuration. Alternatively, specialized services can clone the software from your old CEM to a used unit.
   Est. part cost: $800-$1500

Rare But Worth Checking

• Faulty Engine Control Module (ECM): While the code blames the ECM, the module itself is rarely the true cause. It should only be suspected after all wiring, power, ground, and other network modules have been thoroughly checked.
• Faulty Third-Party Component: A non-OEM electronic component (e.g., a cheap aftermarket water pump or alternator) that communicates on a vehicle sub-network can create electrical noise and disrupt the main CAN bus, leading to communication codes.

Diagnosis Steps

1. Check for other DTCs. A full vehicle scan with a Volvo-specific tool can provide clues. Multiple 'U' codes point to a network-wide problem. Look specifically for VCM-U105000.
2. Test the 12V Main Battery. Check voltage (should be >12.4V) and perform a load test. This is the most common and easiest-to-fix cause.
3. Inspect Battery Terminals and Main Ground Straps. Ensure all connections are clean, tight, and free of corrosion. Poor grounds are a common cause of communication failures.
4. Address VCM-related warnings. If the 'Volvo On Call Service Required' message is present, investigate and replace the VCM backup battery.
5. Check Fuses. Inspect all fuses related to the ECM, CEM, and other control modules in the engine bay, under the glove compartment, and in the trunk.
6. Perform a CAN Bus Integrity Test. With the battery disconnected, measure resistance between Pin 6 (CAN High) and Pin 14 (CAN Low) on the OBD-II port. A reading of ~60 Ohms indicates the main bus wiring and terminating resistors are likely intact. A reading of 120 Ohms suggests a break in the circuit or a faulty terminating resistor in one of the modules.
7. Visually Inspect Wiring Harnesses. Check for physical damage, corrosion, or loose connections at the ECM, CEM, and under the passenger side carpet where water intrusion can sometimes occur.
8. If all else fails, seek professional help to test the individual modules (ECM, CEM) for internal failure using specialized diagnostic equipment.

Parts You'll Likely Need

• AGM 12V Main Battery — The extreme voltage sensitivity of the SPA platform makes a weak battery the number one cause of network communication faults like U0100.
  Trusted brands: Volvo Genuine, Bosch, Interstate
  OEM price range: $350-$450
  Aftermarket price range: $250-$350
• VCM (Telematics) Backup Battery (OEM #31450445 (superseded by 32279613)) — This small battery is a common failure item that can disrupt the entire CAN network. Its failure is often indicated by a 'Volvo on Call Service Required' message and DTC VCM-U105000.
  Trusted brands: Volvo Genuine
  OEM price range: $60-$100

Related Codes That Often Appear With This One

• U0101 — Lost Communication with TCM (Transmission Control Module). The TCM and ECM are on the same high-speed CAN bus. A network-wide failure will almost always cause both codes to appear together.
• U0121 — Lost Communication with ABS Control Module. Like the TCM, the ABS module is on the high-speed CAN bus and loses communication during a network failure.
• U0140 — Lost Communication with Body Control Module (or CEM). This indicates a widespread network problem affecting multiple key gateways.
• VCM-U105000 — This Volvo-specific code indicates an internal fault with the VCM backup battery and is a direct pointer to one of the most common causes of U0100 on this platform.

Technical Service Bulletins (TSBs) & Recalls

• R39917 - VCM Software Error
• S39893 - VCM Backup Battery Service Action

Platform-Specific Known Issues

• Recall R39917: A software error in the Vehicle Connectivity Module (VCM) could cause improper function of telematics and driver support systems. While not directly causing U0100, it highlights the VCM's critical role and sensitivity.

Mechanic-Grade Diagnostic Values

• CAN Bus Network Resistance — expected: ~60 Ω. Failure: A reading of ~120 Ω indicates an open circuit or one missing terminating resistor. A reading near 0 Ω indicates a short between CAN High and CAN Low wires.
• CAN Bus Voltage (Key On, Engine Off) — expected: CAN High (Pin 6): ~2.6V to GND. CAN Low (Pin 14): ~2.4V to GND.. Failure: Voltages on both lines being the same can indicate a short between them. Significant deviation from these values suggests a module or wiring fault.
• CAN Wire Resistance to Ground — expected: Infinite resistance (Open circuit / O.L.). Failure: Any low resistance reading indicates a short to ground on either the CAN High or CAN Low line.
• ECM/PCM Power Supply Voltage — expected: 12.0–14.5 V. Failure: Voltage sag below 10V during cranking can cause communication modules to drop offline.

Hidden / Shadow Codes Worth Checking

• VCM-U105000: Indicates an internal fault with the VCM backup battery. This is a primary indicator that the VCM battery is the root cause of network communication issues. (see via Requires a Volvo-specific scan tool like VIDA.)
• CEM-DF series (e.g., CEM-DF13 to DF16): These codes indicate a network fault detected by the Central Electronic Module, specifically pointing to short circuits to ground or voltage on the high-speed CAN bus. (see via Requires a Volvo-specific scan tool like VIDA.)

Scan Tool Commands That Help

• Volvo VIDA: VCM Backup Battery Replacement Software Download — This procedure is required after replacing the VCM backup battery. It involves downloading a specific Software Product (SP) to reset the internal battery age counter in the VCM and clear the persistent 'Volvo on Call Service Required' message. Volvo TJ 36916.2.0 specifies SP 32398268 for SPA platform vehicles.
• Volvo VIDA: CEM Reload — If the Central Electronic Module (CEM) is replaced, a 'CEM Reload' must be performed. This downloads the vehicle-specific software and configuration from Volvo's servers to the new module, binding it to the car.
• Volvo VIDA: Fault Trace and Delivery Tabs — Within VIDA, the 'Fault Trace' tab is used to read all DTCs from all modules. After repairs, navigating to the 'Delivery' tab allows a technician to erase all fault codes from the entire network.

Wiring & Ground Locations

• VCM (Vehicle Connectivity Module) — Located in the trunk, behind the right-side trim panel on the S90.. This module houses the backup battery that is a primary cause of U0100. Its connectors and wiring can be inspected during battery replacement.
• CEM (Central Electronic Module) — Located under the passenger side dashboard, behind the carpet/kick panel.. The CEM is a central network gateway. Checking its connectors for corrosion or looseness is a key diagnostic step. Water intrusion in this area can cause widespread network faults.
• Main Ground Points — Key ground points for the SPA platform are welded studs throughout the body. A thorough investigation of ground quality is crucial for electrical stability.. Poor grounding can introduce electrical noise and voltage drops, disrupting CAN bus communication and triggering U-codes.

Real Owner Repair Stories

• YouTube user comment on 'Volvo ON CALL SERVICE REQUIRED' video (2018 Volvo XC90 (SPA Platform, similar to S90)) — 'ON CALL SERVICE REQUIRED' message on the dash.
  ❌ Tried (didn't work) Initially quoted $700-$800 by the dealer for the fix.
  ✅ What actually fixed it The owner replaced the VCM backup battery (Part No. 31450445) themselves for about $100. They noted that a subsequent software update from the dealer is required to reset the internal battery life counter within the VCM to prevent the warning from returning prematurely.

OEM Part Supersession History

• 31450445 → 32279613 — Standard part revision and update by Volvo.
  Heads up: Both parts are functionally interchangeable for replacing the VCM backup battery.

Model Year Variations Within This Range

• 2017-2021: Volvo Technical Journal TJ 36916.2.0 specifically lists chassis ranges for various models from these years as being affected by the VCM backup battery issue, suggesting these earlier SPA platform vehicles are more prone to the failure.

Diagnostic Flowchart

Other Known Issues on This Vehicle

Issues unrelated to this code that are worth knowing about as an owner of this generation:

• Excessive Oil Consumption (2015-2016 Drive-E Engines) 🔴 High — Common on early Drive-E 4-cylinder engines around 80k-125k miles, though the S90's model years are generally outside the highest-risk window. The root cause is clogged piston oil control rings. (Ref: Volvo issued an extended warranty and TSB TJ 31233 for this issue on affected models.)
• Sensus Infotainment System Lag/Freezing 🟠 Medium — Very common on early model years (2017-2019). Symptoms include slow response, random reboots, or a blank screen. Often addressed with software updates, but can sometimes indicate hardware issues. (Ref: Multiple software updates have been released. TSB TJ 36555 addresses the iCUP getting stuck in recovery mode.)
• Premature Brake Rotor Wear/Vibration 🟠 Medium — Often reported on 2017-2018 models. Owners report vibration from the rear brakes and faster-than-expected wear. (Ref: TSB TJ 20803.21.0 provides a diagnostic test schedule for speed-dependent vibrations.)
• Sunroof Drain Gurgling/Leaking 🟡 Low — Some owners report a gurgling noise from the sunroof area when driving in the rain, which can lead to water ingress if the drains are clogged or improperly designed. (Ref: TSB TJ 34532 describes a fix that involves extending the front sunroof drain hoses to prevent the issue.)
• 12V Battery Drain (iCUP Vehicles) 🟠 Medium — A known issue on vehicles equipped with the Android Automotive (iCUP) infotainment system where the 12V battery can drain unexpectedly. (Ref: TSB TJ 36189 addresses this specific 12V battery drain issue.)

Used vs. New Parts: Buying Guide for This Vehicle

When a used part is the smart pick: For this specific fault, using used parts is generally not recommended for the primary electronic modules. A used part may make sense for simple mechanical components or trim pieces that need to be removed for access.

Donor-vehicle mileage cap: roughly under 100000 miles for the part to have meaningful remaining life.

What to inspect on the donor part:

• Verify the donor vehicle was not in a flood or had significant electrical fire damage.
• For electronic modules, ensure the part number matches exactly.
• Obtain the VIN of the donor car if possible, as it may be needed for programming.

OEM-only on this vehicle (don't cheap out):

• Central Electronic Module (CEM): Used CEMs are VIN-locked. A used one cannot be simply installed. It either requires a 'CEM Reload' from a dealer (which they may refuse to do on a used part) or specialized cloning of the original module's software to the donor unit.
• Engine Control Module (ECM): Similar to the CEM, the ECM is VIN-locked and requires dealer programming for a new unit or cloning for a used one.
• VCM Backup Battery: Given the low cost of a new OEM part ($50-$100) and its known limited lifespan, installing a used battery is not cost-effective and highly likely to fail soon.

Aftermarket brands forum-validated for this vehicle:

• For the main 12V AGM battery, established brands like Bosch and Interstate are reliable alternatives to the Volvo Genuine part.

Brands owners have reported issues with on this vehicle:

• For the VCM backup battery, unbranded, no-name options from direct-from-China marketplaces are available but carry a higher risk of premature failure compared to the OEM part.

Real Owner Stories

Aggregated from forums and TSBs cited above. Mileages and costs reflect what owners reported in those sources.

Related OBD-II Codes

• VCM-U105000 — A Volvo-specific fault code directly related to the VCM internal backup battery failure, often appearing alongside network communication issues.
• U1050 — Often triggered in conjunction with U0100 when the Vehicle Connectivity Module (VCM) backup battery fails or loses communication.
• U0101 — Communication loss code that may appear simultaneously with U0100 when the high-speed CAN bus is disrupted by low voltage or wiring issues.
• U0121 — Communication loss with the ABS module, which may illuminate multiple warning lights simultaneously during a network-wide voltage drop or CEM failure.

Frequently Asked Questions