U0100 on 2014-2026 Ram ProMaster: Causes for Lost Communication with ECM/PCM and Fixes

What's Unique About the 2014-2026 Ram ProMaster

For the 2018 model year specifically, the Ram ProMaster was subject to a critical recall (NHTSA 18V-524 / FCA recall U87) for a faulty voltage regulator inside the PCM, which directly causes the U0100 code and can lead to stalling or a no-start condition. This recall affected over a dozen other FCA vehicles from the same period. Beyond that specific recall, ProMasters, like other vehicles in the FCA/Stellantis family, can be sensitive to low battery voltage and are known to have issues with wiring harness corrosion or faults in the Totally Integrated Power Module (TIPM) that can trigger this code. Furthermore, platform mates like the Ram 1500 show a pattern of U0100 codes caused by water intrusion in the driver's footwell corroding a central network connector called the 'Star Connector'.

Generation note: The 2014-2026 model years represent a single generation of the Ram ProMaster in North America (based on the Fiat Ducato), though it has received several facelifts. The diagnostic approach is similar across all years, with the notable exception of the 2018 model year due to a specific PCM recall.

Symptoms You May Notice

• Engine will not start (no-crank or cranks but won't fire).
• Engine stalls intermittently while driving.
• Check Engine Light is on.
• Multiple warning lights on the dashboard may illuminate simultaneously (e.g., ABS, stability control).
• Transmission may be stuck in a single gear (limp mode).
• Erratic or dead instrument cluster gauges.
• Scan tool cannot communicate with the ECM/PCM.
🎬 Watch: Troubleshooting a no-start and stuck key with a ground wire.

Most Likely Causes

1. Faulty Powertrain Control Module (PCM) - 2018 Models 🔴 High Probability → Shop Engine Control Module (ECM) A specific batch of PCMs was manufactured with a suspect voltage regulator chip on the circuit board, leading to recall NHTSA 18V-524 (FCA recall U87).
   How to confirm: Contact a Ram dealer or use the NHTSA website with your VIN to see if your vehicle is part of this recall. The recall involves replacing the PCM.
   Typical fix: Replace and reprogram the Powertrain Control Module. This is covered for free by the dealer if the recall is open for your vehicle.
   Est. part cost: $0 (if under recall)
2. Weak or Faulty Battery 🟡 Medium Probability → Shop Vehicle Battery Modern vehicle electronics are highly sensitive to voltage. A battery that is failing, has low charge, or has corroded terminals can cause unpredictable communication errors between modules, especially after exposure to cold weather.
   How to confirm: Test the battery with a multimeter. A healthy battery should show ~12.6 volts with the engine off. With the engine running, the charging system should produce ~13.5-14.5 volts. Ensure terminals are clean and tight.
   Typical fix: Recharge or replace the battery. Ensure battery terminals are clean and tight.
   Est. part cost: $150-$350
3. Corroded or Loose Ground Straps / Power Connections 🟡 Medium Probability → Shop Engine Ground Strap The primary engine ground strap on the ProMaster, which runs from the transmission case to a bolt on the transmission mount, is a known potential failure point. 🎬 Watch: A guide to locating and inspecting the ground strap. Corrosion or looseness here can corrupt data signals. Water intrusion in the footwell area has also been noted as a cause of circuit corrosion.
   How to confirm: Visually inspect all major ground connections. Specifically, locate the braided strap at the transmission and ensure it is tight and free of corrosion at both ends. A temporary fix for testing is to use a jumper cable to create a new ground from the engine block to the chassis.
   Typical fix: Clean the connection points to bare metal and re-secure the ground straps. Replace corroded straps or add a redundant ground cable.
   Est. part cost: $20-$100
4. Damaged CAN Bus Wiring Harness ⚪ Low Probability Wiring harnesses can chafe against engine or chassis components, particularly near A/C lines or where the harness passes through the firewall, causing the two CAN bus wires to short together or to ground.
   How to confirm: Perform a detailed visual inspection of the wiring harness. Advanced diagnosis involves checking for 60 ohms of resistance across the CAN High and CAN Low pins at the OBD-II port.
   Typical fix: Repair the damaged section of the wiring harness and protect it from future chafing.
   Est. part cost: $20-$200

Rare But Worth Checking

• Faulty ABS or other module: A failing module, such as the Anti-lock Brake System (ABS) module, can broadcast corrupt data onto the network or short the bus internally, preventing other modules from communicating and falsely implicating the PCM. A full-system scan is needed to check for codes in other modules.
• Faulty Totally Integrated Power Module (TIPM): → Shop Fuse Box The TIPM is the main fuse and relay center. Internal failures can cut power to the PCM, causing a U0100 code. This is a known issue on many FCA vehicles and can cause a wide range of electrical gremlins.
• Corroded Star Connector / Junction Block: On related Ram platforms, a primary cause of U0100 is a corroded 'Star Connector' (CAN bus junction) located behind the driver's side kick panel. 🎬 See how to find and fix a corroded star connector. Water intrusion from a leaky windshield or clogged drain can cause corrosion on the pins, breaking network communication. While not documented specifically for ProMaster as often, it is a critical diagnostic path given the shared architecture.

Diagnosis Steps

1. Check for Recalls: If you have a 2018 model, immediately check if your VIN is affected by recall NHTSA 18V-524.
2. Check Battery Health: Test the battery voltage with the engine off (should be ~12.6V) and running (should be ~13.5-14.5V). Clean any corrosion from the terminals and ensure they are tight. A weak battery is a very common trigger.
3. Scan for All Codes: Use a high-quality OBD-II scanner capable of reading codes from all vehicle modules (PCM, TCM, ABS, BCM, etc.). Note all communication codes present.
4. Inspect Grounds and Connectors: Visually inspect the main battery and engine ground straps. Pay special attention to the braided ground strap from the transmission case to the chassis mount. Inspect the PCM connectors for corrosion, moisture, or pushed-out pins.
5. Inspect Wiring Harness: Carefully check the wiring harness for any signs of chafing, melting, or rodent damage, especially where it routes near hot or moving parts like A/C lines.
6. Inspect Star Connector (Advanced): Remove the driver-side kick panel and inspect the CAN bus junction block ('Star Connector') for any signs of green or white corrosion caused by water intrusion.
7. Advanced Diagnostics (CAN Bus Resistance Check): Disconnect the negative battery terminal. Set a multimeter to Ohms (Ω). Probe between Pin 6 (CAN High) and Pin 14 (CAN Low) at the OBD-II port. A healthy network should read approximately 60 Ohms. A reading of ~120 Ohms indicates an open in the circuit or a faulty terminating resistor. A reading near 0 Ohms indicates the CAN High and Low wires are shorted together.

Parts You'll Likely Need

• Powertrain Control Module (PCM) (OEM #68345830AB (example for 2018, VIN specific)) — This is the required fix for the 2018 model year recall. For other years, it's replaced only after all other causes (wiring, power, grounds) have been ruled out. Part numbers are VIN-specific.
  Trusted brands: Mopar
  OEM price range: $800-$1200
  Aftermarket price range: $500-$900
• Battery — A weak or failing battery is a very common cause of network communication codes due to low system voltage.
  Trusted brands: Interstate, Duralast, DieHard
  OEM price range: $250-$400
  Aftermarket price range: $150-$350
• Engine Ground Strap — The primary engine ground can corrode or break, leading to unstable voltage for all modules and sensors.
  Trusted brands: Mopar, Dorman
  OEM price range: $40-$80
  Aftermarket price range: $15-$40

Related Codes That Often Appear With This One

• U0101 — Lost Communication with TCM (Transmission Control Module). The TCM is on the same high-speed network, so a network failure often takes both the ECM and TCM offline.
• U0121 — Lost Communication With Anti-Lock Brake System (ABS) Control Module. This can appear if the entire network is down or if the ABS module itself is the source of the failure.
• U0140 — Lost Communication with Body Control Module (BCM). Its presence suggests a widespread network problem rather than an isolated PCM issue.

Technical Service Bulletins (TSBs) & Recalls

• NHTSA 18V-524 / FCA Recall U87: Title: 'Voltage Regulator may Fail and Cause Stall'. This is the primary recall for the 2018 model year, involving the replacement of the PCM due to a faulty internal voltage regulator chip.
• Ram TSB #18-037-16 REV. A: While for Ram 2500/3500 trucks, it addresses a similar 'No crank/No start' condition with code U0100, which is corrected by a software update, showing that software can also be a cause on related platforms.
• Bulletin #18-091-16: Notes that U0100 can be present alongside various transmission solenoid and pressure sensor codes, such as P1775 and P1776, on related heavy-duty platforms.
• Bulletin #08-037-21: Describes a scenario where U0100-00 (Lost Communication With ECM/PCM) occurs simultaneously with U0140-00 (Lost Communication With Body Control Module) and U0102-00 (Lost Communication With Transfer Case Control Module).

Platform-Specific Known Issues

• Recall NHTSA 18V-524 / FCA U87: Affects some 2018 Ram ProMaster models. The PCM may have a faulty voltage regulator that can cause the engine to stall or not start.
• Ground Strap Corrosion: The primary engine ground strap, located on the transmission, is a common point of failure due to corrosion or looseness, leading to a host of electrical issues including U0100.
• Potential for Star Connector Corrosion: Based on issues with platform mates, the CAN bus junction block behind the driver's kick panel is a potential failure point if the vehicle has any water leaks in that area.
• Software-Induced No-Start: As documented in Bulletin #18-037-16, enhanced software was released for related Ram models to address a "No crank/No start" issue specifically associated with U0100.

Mechanic-Grade Diagnostic Values

• CAN C Bus Resistance — expected: 53.5 to 67 Ohms between Pin 6 and Pin 14 of the OBD-II port (ignition off, battery disconnected).. Failure: A reading of ~120 Ohms indicates one of the two terminating resistors is offline. A reading near 0 Ohms indicates a short between the CAN High and Low wires.
• CAN C+ (High) Voltage — expected: ~2.5V to 3.0V DC with key on, engine off, measured between Pin 6 of OBD-II port and chassis ground.. Failure: Significant deviation, being stuck high (near 5V) or low (near 0V), indicates a short to power or ground.
• CAN C- (Low) Voltage — expected: ~2.0V to 2.5V DC with key on, engine off, measured between Pin 14 of OBD-II port and chassis ground.. Failure: Significant deviation, being stuck high or low, indicates a short circuit.
• PCM Ground Circuit Resistance — expected: Less than 0.1 Ohms between the PCM ground pins and a clean chassis ground point.. Failure: Higher resistance indicates a poor ground connection, which can cause module communication errors.

Scan Tool Commands That Help

• wiTECH (FCA/Stellantis Dealer Tool) or AlfaOBD: Vehicle Scan Report / Read All DTCs — Use this as the first step to see a complete list of which modules are reporting the U0100 code. If only one module reports it, the issue may be with that module. If many modules report it, it points to a network-wide failure.
• wiTECH (FCA/Stellantis Dealer Tool): Check for Flashes — After confirming power, grounds, and CAN bus wiring are intact, use this function to check if there are any available software updates for the PCM or other modules. Communication glitches are sometimes resolved with a software update.

Wiring & Ground Locations

• Primary Engine Ground Strap — A braided strap running from the transmission case to a bolt on the upper side of the transmission mount. It is best accessed by removing the driver's side headlight assembly.. This is the main ground path for the engine and its electronics, including the PCM. Corrosion or looseness here creates an unstable ground reference, corrupting data signals and causing communication codes like U0100.
• Star Connector (CAN Bus Junction) — On the related Ram 1500 platform, this is a bank of connectors located behind the driver's side kick panel, near the parking brake. This is a high-probability location to check for corrosion on the ProMaster as well.. This acts as a central hub for the CAN bus network. Water intrusion from a leaky windshield or clogged drain can corrode the pins, causing intermittent or total loss of communication between modules.
• PCM Connector C1 (Example from Ram platform) — The main large connector at the Powertrain Control Module.. Specific pins can be tested for power, ground, and CAN signals. For example, on a similar Ram, power is on pins 80, 81, 82, 84; ground is on pins 52, 53; CAN High is on pin 57; and CAN Low is on pin 33. These are critical points for advanced diagnosis.
• ProMaster City CAN-C Connector (Recall S24040816) — On 2015-2016 ProMaster City models, this connector was originally located under the driver's seat where it was prone to moisture and corrosion.. While a different model, this establishes a precedent for FCA placing critical CAN connectors in locations vulnerable to water damage, making under-seat areas a place to inspect on the full-size ProMaster.

Real Owner Repair Stories

• YouTube user 'T&N Automotive' (2014 Ram ProMaster) — No-start condition.
  ❌ Tried (didn't work) Initial diagnosis pointed towards a starter or battery issue.
  ✅ What actually fixed it A redundant ground cable was added, running from one of the starter mounting bolts directly to a solid point on the vehicle's chassis frame. This provided a sufficient ground path for the starter and resolved the no-start.
• YouTube channel 'Pine Hollow Auto Diagnostics' (2021 Ram ProMaster 3.6L) — No-start, key stuck in ignition, no communication with scan tool.
  ✅ What actually fixed it The final fix was not posted, but the diagnosis found the root cause: The CAN bus resistance measured 120 Ohms, indicating an open circuit / missing terminating resistor. The technician discovered significant water droplets on the PCM connector and nearby harnesses in the driver's footwell area, strongly suggesting water intrusion had corroded a connection or the PCM itself.
• YouTube channel 'Flying Wrenches' (2019-2022 Ram 1500 (related platform)) — Intermittent no-crank, no-start, U0100 code.
  ❌ Tried (didn't work) Assuming the PCM was faulty.
  ✅ What actually fixed it The Star Connector (CAN bus junction block) behind the driver's kick panel was corroded from water intrusion. Wiggling the connector temporarily restored communication. The permanent fix was to clean the connector pins with electrical contact cleaner or replace the connector entirely (Mopar P/N 68324484AA).
• NHTSA ODI #11662767 — An owner reported a communication or control module fault within the vehicle's network involving a cascade of codes including U0100, U0159, U0140, U0137, U0102, U10121, and U0101.

"I Checked Everything" — The Actual Cause

• A common scenario for this code is that all static electrical tests (CAN resistance, voltage checks, ground continuity) pass, yet the fault persists. This can happen when a ground wire breaks *inside* its crimped terminal lug. The wire looks secure and may even have continuity at rest, but when the engine torques under load (e.g., shifting into gear), the connection momentarily separates, causing the PCM to lose its ground reference and triggering the U0100 code. The fix is to physically pull on the ground wires at their terminals; a faulty one will pull out of the lug.

When the Usual Fixes Don't Work

• While U0100 directly implicates the PCM, master technicians and experienced owners strongly advise against replacing the PCM until all other possibilities are exhausted. There are numerous documented cases where a persistent U0100 with a no-start condition was ultimately resolved by simple, low-cost fixes. For example, one owner fixed the issue by adding a $20 redundant ground cable from the engine block to the chassis, bypassing a corroded factory ground that was causing the problem. In another common scenario on a related platform, the fix was cleaning a corroded Star Connector (a network hub) located in the driver's kick panel, which had been contaminated by a water leak. These examples prove that the root cause is very often in the supporting infrastructure (power, ground, wiring) and not the expensive computer itself.

OEM Part Supersession History

• 68345830AA → 68345830AB, 68345830AC, 68345830AD, 68345830AE — Standard revision and update process for electronic modules.
  Heads up: These part numbers are generally interchangeable for the 2018 model year, but the module must be programmed with the vehicle's VIN and configuration. Failure to program will result in a no-start condition due to the SKIM (Sentry Key Immobilizer Module) security system.

Model Year Variations Within This Range

• 2018: This model year was subject to recall NHTSA 18V-524 for an internal PCM fault. The PCM is the most likely cause of U0100 on these specific vans.
• 2015-2016 (ProMaster City): A recall (S24040816) was issued to relocate a CAN-C bus connector from under the driver's seat to a less moisture-prone location under the instrument panel. This highlights a known design weakness in the family that could be relevant to full-size ProMaster diagnostics.
• 2021+: Later models may be equipped with a dedicated Consumer Connection Point (CCP) at the passenger B-pillar for upfitter use. Improperly tapping into vehicle wiring instead of using this point could be a source of network faults on newer vans.

Diagnostic Flowchart

Real Owner Stories

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

Related OBD-II Codes

• U0101 — Lost Communication with TCM. Often appears alongside U0100 because CAN bus failures can cause the transmission to get stuck in a single gear (limp mode).
• U0121 — Lost Communication with ABS Control Module. Frequently triggered with U0100, as noted by the simultaneous illumination of ABS and stability control warning lights during a network failure.
• U0140 — Lost Communication with Body Control Module (BCM). Commonly accompanies U0100 when the Star Connector (CAN bus hub) suffers from water intrusion and corrosion.
• P0562 — System Voltage Low. Directly related to the weak or faulty battery cause, as low voltage is a primary trigger for module communication dropouts.
• U0001 — High Speed CAN Communication Bus. Appears when the CAN bus wiring harness chafes and shorts together or to ground, disrupting all module communication.

Frequently Asked Questions