U0100 on 2020-2021 Ford Explorer Police Interceptor: Lost Communication with PCM Causes and Fixes

What's Unique About the 2020-2021 Ford EXPLORER POLICE INTERCEPT

For this specific vehicle, particularly the 3.3L Hybrid models, the U0100 code is frequently not a hardware problem. Ford issued Technical Service Bulletin TSB 21-2375 (superseding TSB 20-2429) acknowledging that a software issue within the Powertrain Control Module (PCM) can cause the Battery Energy Control Module (BECM) to log this code. Additionally, another bulletin, SSM 49519, points to a software issue in the Gear Shift Module (GSM) that can cause U0100 on vehicles with 10-speed transmissions built before late October 2020. This makes checking for software updates a mandatory first step, potentially saving significant expense on unnecessary hardware diagnosis.

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 (Malfunction Indicator Lamp) is on.
• Powertrain Malfunction (Wrench) light is on.
• Vehicle may not start, or the starter may not engage.
• Engine may stall, run rough, or misfire.
• Reduced engine power or 'limp mode'.
• Harsh or erratic transmission shifting.
• Multiple warning lights on the dashboard (ABS, traction control, etc.).
• Inability to communicate with the PCM using a scan tool.
🎬 Watch: A breakdown of common causes and fixes for U0100

Most Likely Causes

1. PCM/GSM Software Glitch 🔴 High Probability Ford TSB 21-2375 (superseding 20-2429) directly identifies a PCM software issue as the cause for the U0100 code being stored in the BECM on 2020-2021 3.3L Hybrid models. Separately, TSB SSM 49519 identifies a Gear Shift Module (GSM) software issue on some 2020-2021 models that can also log U0100.
   How to confirm: A Ford dealer or a shop with access to Ford's service information can check if TSB 21-2375 or SSM 49519 applies to the vehicle's VIN and build date.
   Typical fix: Reprogram the Powertrain Control Module (PCM) or Gear Shift Module (GSM) with the latest software version. This is a service performed by a dealer.
   Est. part cost: $0-$300
2. Weak or Failing Battery 🟡 Medium Probability Modern vehicles are highly sensitive to system voltage. A weak battery can cause unpredictable communication errors between modules before it's weak enough to cause a no-start condition. This is one of the most common causes for generic U-codes.
   How to confirm: Test the 12-volt battery with a digital multimeter or a professional battery tester. The voltage should be above 12.4V with the engine off. Perform a load test to check its health. A voltage reading of a dead battery on a 2020 Explorer was captured in a video at 4.3V before a jump start.
   Typical fix: Replace the 12-volt battery. These vehicles use an AGM (Absorbent Glass Mat) battery, which must be replaced with the same type. After replacement, a Battery Monitoring System (BMS) reset using a scan tool is required.
   Est. part cost: $200-$400
3. Wiring Harness or Connector Issue ⚪ Low Probability Police Interceptors are often fitted with additional equipment (upfitting), which can sometimes lead to wiring being disturbed, chafed, or damaged during installation or service. Forum users have also reported finding loose factory ground connections causing multiple communication codes.
   How to confirm: Visually inspect the wiring harnesses connected to the PCM and other major modules for signs of chafing, corrosion, or rodent damage. Check main ground straps for tightness and corrosion. 🎬 See how a simple wiring issue can mimic a dead PCM Check the resistance between pins 6 and 14 on the OBD-II port; it should be approximately 60 ohms.
   Typical fix: Repair the damaged section of the wiring harness and ensure all connectors and grounds are clean and securely seated.
   Est. part cost: $50-$800
4. Faulty Powertrain Control Module (PCM) ⚪ Low Probability
   How to confirm: This is diagnosed by exclusion. If all software updates have been performed, and all wiring, grounds, and power feeds to the PCM test good, the module itself is the likely culprit.
   Typical fix: Replace the PCM. The new module will require programming by a dealer or qualified technician to work with the vehicle.
   Est. part cost: $800-$2000

Rare But Worth Checking

• Faulty Gateway Module (GWM):
• Poor Ground on AWD Module:

Diagnosis Steps

1. Check the 12V battery voltage and perform a load test. A weak battery is a common cause of network codes.
2. Scan all vehicle modules for DTCs. Note which modules are reporting a loss of communication with the PCM.
3. For 3.3L Hybrid models, check if TSB 21-2375 applies. If so, the primary fix is a PCM software update performed by a dealer.
4. Check for other applicable TSBs, such as SSM 49519 for GSM software issues on models with 10-speed transmissions.
5. Inspect all fuses related to the PCM, TCM, and other control modules.
6. Visually inspect the wiring harness to the PCM for any signs of physical damage, corrosion, or loose connections. Pay special attention to areas where upfitter equipment may have been installed.
7. Check for proper power and ground connections at the PCM connector and main chassis ground points. A loose ground can cause intermittent communication faults.
8. Measure the CAN bus resistance at the OBD-II port (pins 6 and 14). A reading of approximately 60 ohms indicates the terminating resistors are intact. A reading of 120 ohms 🎬 Watch: Top 5 ways to diagnose lost communication with the PCM suggests an open circuit or a faulty module.
9. If multiple modules on different networks are failing, investigate the Gateway Module (GWM) as a potential cause.
10. If all wiring and software checks pass, the final step is to diagnose a potential internal failure of the PCM.

Parts You'll Likely Need

• PCM Software Update — This is the most common fix for 2020-2021 Hybrid models as specified by Ford TSB 21-2375.
  Trusted brands: Ford (Dealer Service)
  OEM price range: $150-$300
• AGM Battery (OEM #BAGM-94RH7-800) — Low system voltage from a weak battery is a frequent cause of network communication codes on modern vehicles.
  Trusted brands: Motorcraft, Interstate, DieHard
  OEM price range: $250-$350
  Aftermarket price range: $200-$300
• Powertrain Control Module (PCM) — If software and wiring issues are ruled out, the PCM itself may have an internal fault, requiring replacement.
  Trusted brands: Motorcraft
  OEM price range: $800-$2000
  Aftermarket price range: $500-$1200

Related Codes That Often Appear With This One

• U0073 — Control Module Communication Bus 'A' Off. This code indicates a general CAN bus failure, whereas U0100 is specific to the loss of communication from the PCM. Seeing both points to a more widespread network problem.
• U0101 — Lost Communication with TCM. The Transmission Control Module (TCM) and PCM are on the same high-speed network. A network wiring problem or a failing battery can cause communication loss to both modules simultaneously.
• U0155 — Lost Communication With Instrument Panel Cluster (IPC) Control Module. TSB SSM 49519 specifically lists this code alongside U0100 as a symptom of a Gear Shift Module (GSM) software issue.

Technical Service Bulletins (TSBs) & Recalls

• TSB 21-2375: For 2020-2021 3.3L hybrid models, an illuminated MIL with DTC U0100 stored in the BECM may be due to PCM software, requiring an update. This bulletin supersedes TSB 20-2429.
• TSB SSM 49519: For some 2020-2021 Explorers built on or before 29-Oct-2020, DTC U0100 (among others) can be caused by a software fault in the Gear Shift Module (GSM), requiring a reprogram.

Platform-Specific Known Issues

• TSB 21-2375: (Supersedes TSB 20-2429) Some 2020-2021 Explorer/Police Interceptor Utility vehicles equipped with a 3.3L hybrid engine and built on or before 21-Oct-2020 may exhibit an illuminated malfunction indicator lamp (MIL) with diagnostic trouble code (DTC) U0100 stored in the battery energy control module (BECM).

Mechanic-Grade Diagnostic Values

• HS-CAN Bus Resistance — expected: ~60 Ohms (± 5 Ohms). Failure: A reading of ~120 Ohms indicates an open circuit or a missing terminating resistor. A reading significantly lower than 60 Ohms suggests a short between the CAN high and low wires.
• CAN Bus Voltage (Key On, Engine Off) — expected: CAN High (Pin 6) and CAN Low (Pin 14) should both show approximately 2.5V to ground.. Failure: A wire stuck near 0V or a higher voltage (5V/12V) indicates a short to ground or power, respectively.
• PCM Ground Circuit Resistance — expected: Less than 0.2 Ohms. Failure: Higher resistance indicates a poor ground connection, which can cause intermittent module resets and communication faults.

Hidden / Shadow Codes Worth Checking

• Module reporting the code: With a generic U0100 code, the most critical piece of 'hidden' information is *which module* is reporting the loss of communication. The TSB for the hybrid model specifically notes that the U0100 is stored in the Battery Energy Control Module (BECM). If the code is stored in the ABS module or TCM, it points the diagnosis in a different direction. A basic code reader may only show the code, while a professional scan tool will show which module logged it. (see via Ford IDS/FDRS or a high-end professional scan tool with the ability to poll all modules individually.)
• U0100 in ACM: Per TSB SSM 48916, if DTC U0100 is found stored *only* in the Audio Control Module (ACM) with no other symptoms, the code should be disregarded as it does not affect vehicle operation. (see via Ford IDS/FDRS or professional scan tool.)

Scan Tool Commands That Help

• Ford IDS/FDRS: Network Test — This is a primary diagnostic step. The tool pings all modules on the various networks and provides a topology map showing which modules are communicating and which are not, quickly isolating the scope of the fault.
• Ford IDS/FDRS: PCM/GSM Reprogramming — This function is used to perform the software update specified in TSBs 20-2429 and SSM 49519, which is the most common fix for this code on affected vehicles.
• Ford IDS/FDRS: Programmable Module Installation (PMI) — This is required if the PCM or another network module must be replaced. It transfers vehicle-specific configuration data from the old module to the new one to ensure proper function.

Wiring & Ground Locations

• G108 / G111 — Located on the right side of the engine compartment, on the fender apron near the battery.. This is a major chassis ground point for several engine bay components, including modules. A loose or corroded connection here can cause widespread electrical issues, including network faults.
• G201 / G204 — Located inside the cabin, at the base of the left or right A-pillar, behind the kick panel.. These are primary interior ground points for many modules located inside the passenger compartment. A poor connection here can disrupt communication for modules like the GWM or BCM.
• C175B — This is the main electrical connector for the Powertrain Control Module (PCM).. All power, ground, and network communication wires for the PCM pass through this connector. Checking for backed-out pins, corrosion, or poor terminal tension at this specific connector is a critical diagnostic step.
• Upfitter Harnesses — Varies, but typically routed through the firewall and connected to power distribution points under the dash or in the rear cargo area.. On Police Interceptor models, aftermarket equipment for lights, sirens, and radios can be improperly spliced into vehicle wiring, disturbing CAN bus circuits or creating ground loops that cause communication errors. The Ford Modifier Guide explicitly warns against splicing into CAN bus wiring.

Real Owner Repair Stories

• YouTube Comment on 'Causes and Fixes U0100 Code' (2017 Ford Transit (related platform with similar electrical architecture)) — U0100 code, no crank/no start condition.
  ❌ Tried (didn't work) Wiggling the ECU would temporarily allow it to start.
  ✅ What actually fixed it The owner found a bad ground terminal that could be moved by hand. Tightening the ground connection resolved the no-start and the U0100 code.
• YouTube video 'Finding The Hidden CAN Bus Failure That Disabled Everything!' (2017 Ford Explorer (same generation)) — Multiple warning lights, non-functioning door locks, A/C, and liftgate. Multiple 'U' codes for lost communication on the MS-CAN bus (a different network, but the diagnostic principle is identical).
  ❌ Tried (didn't work) Initial scan pointed to multiple failed modules.
  ✅ What actually fixed it The root cause was not a faulty module, but a shorted wire in the harness for the side obstacle detection module in the rear bumper, which had been damaged. Repairing the shorted wires restored communication to all modules on that network. This demonstrates how a fault in one module's wiring can bring down an entire network and cause other modules to log U-codes.

Model Year Variations Within This Range

• 2020-2021 (built on or before 21-Oct-2020): For 3.3L Hybrid models, vehicles built on or before this date are susceptible to the PCM software glitch described in TSB 20-2429, which causes the BECM to store code U0100. Vehicles built after this date should have the updated software from the factory.
• 2020-2021 (built on or before 29-Oct-2020): For models with the 10-speed transmission, vehicles built on or before this date may have a Gear Shift Module (GSM) software issue that causes U0100 and other codes, as noted in SSM 49519. The fix is a GSM reprogram.