U1421 on 2014-2015 Ram 3500: Implausible Ignition Key Off Time Fixes

What's Unique About the 2014-2015 Ram 3500

For this specific generation of Ram HD trucks, the U1421 code is exceptionally well-documented in manufacturer-issued Technical Service Bulletins (TSBs). Ram released multiple software updates for the Powertrain Control Module (PCM) to correct the overly sensitive logic that triggers this code. This indicates it was a known issue from the factory, and the primary solution is a software correction rather than 🎬 See how a professional PCM reflash and programming is performed. a hardware replacement. The high electrical demand of the diesel models also makes them particularly sensitive to battery voltage, a frequent secondary cause.

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
• Code is often found with other DTCs
• Potential issues with remote start functionality, as any active fault can disable it.
• No noticeable drivability problems in most cases

Most Likely Causes

1. Outdated Powertrain Control Module (PCM) Software 🔴 High Probability Manufacturer TSBs #1811322, #1805416, #1807622, #18-099-16, and #18-037-16 REV. A all list U1421 as a code resolved by software updates, confirming it's a known factory logic error.
   How to confirm: A Ram dealership or a qualified shop with access to OEM service information can check the vehicle's current software version against available TSBs using the VIN.
   Typical fix: Reprogramming the PCM with the latest software version. This procedure is often called a 'flash' or 'reflash' and typically takes under an hour.
   Est. part cost: $0
2. Weak or Failing Batteries 🟡 Medium Probability Ram HD trucks, especially diesels with dual batteries, have high electrical demands. Low voltage during startup or shutdown can cause communication glitches between modules, triggering this code. Modern trucks are very sensitive to battery condition, and a weak battery can cause numerous, seemingly unrelated electronic issues.
   How to confirm: Test both batteries individually with a digital multimeter or a carbon pile load tester. A healthy, fully charged battery should read approximately 12.6 volts at rest. It is critical to disconnect the batteries from each other before testing to get an accurate reading. Also, check for loose or corroded battery terminals.
   Typical fix: Replace weak or failing batteries. It is critical to replace both batteries at the same time on diesel models to prevent the older battery from damaging the new one. The common battery group size is H7 (also called 94R).
   Est. part cost: $200-$500 for a pair of quality AGM batteries
3. Aftermarket Electrical Accessories ⚪ Low Probability Improperly installed accessories, especially remote starters, tuners, or alarms tapped into ignition or CAN bus wiring, can interfere with the normal power-down sequence of modules, causing communication errors.
   How to confirm: Inspect the vehicle for any non-factory electronics. If any are found, temporarily disconnect them completely (including any T-harnesses) to see if the code clears and does not return after a few drive cycles.
   Typical fix: Correctly install or completely remove the faulty aftermarket accessory.
   Est. part cost: $0 if removing

Rare But Worth Checking

• Failing Control Module (PCM, BCM, or TIPM): While rare, a module itself can fail and send corrupt data over the network. This is usually a last resort after software, battery, and wiring issues have been ruled out. The diagnostic procedure points to PCM replacement if no other CAN bus faults are present.
• CAN Bus Wiring Issue: An open or shorted wire in the CAN bus network can disrupt communication between modules. This requires advanced diagnostics to trace the wiring harness and check for continuity and resistance between the PCM, BCM, and Instrument Cluster.
• Blown Fuse for Alternator Sense Wire: In some cases, a blown fuse related to the alternator's battery sense circuit can cause system-wide low voltage and trigger various communication codes, including U1421. One owner found a blown mega fuse on the main power distribution stud after changing batteries.

Diagnosis Steps

1. Scan for all DTCs: Note any other codes present, as U1421 is often a companion code set by a primary software or voltage issue.
2. Inspect and Test Batteries: Visually inspect battery terminals for corrosion. Disconnect the batteries from each other and test the voltage (should be ~12.6V) and load capacity of each one. A simple voltage check is often insufficient; a load test is required. Ensure they are fully charged before proceeding.
3. Check for TSBs: Use the vehicle's VIN to check with a dealer or online for applicable TSBs related to U1421 and PCM software updates. The provided NHTSA records are prime examples. TSB 18-037-16 REV. A is a key bulletin for 2015 models.
4. Inspect for Aftermarket Accessories: Look for non-factory wiring, especially around the steering column, fuse box (TIPM), and under the dash for remote starters or performance tuners.
5. Perform Software Update: If a relevant TSB exists and the batteries are healthy, have a dealership or qualified shop perform the PCM software reflash. This is the most common resolution.
6. Advanced Diagnostics: If the code persists after a reflash, the vehicle will need advanced network diagnostics to check the CAN bus wiring and individual modules (PCM, BCM, Cluster) for faults, as outlined in the factory diagnostic procedure.

Parts You'll Likely Need

• Vehicle Battery (OEM #BBH7F001AA (replaces BB0H7730AB, BB0H7730AA)) — Low system voltage is a common cause of communication codes. Diesel models have two batteries that must be replaced in pairs. The common group size is H7/94R.
  Trusted brands: Mopar, Interstate, DieHard, Duralast
  OEM price range: $250-$385 per battery.
  Aftermarket price range: $200-$250 per battery

Related Codes That Often Appear With This One

• P20E8 — Reductant Pressure Too Low - Often included in the same software update TSBs from Ram. [Bulletin #1811322, #1807622, #18-099-16, #18-037-16 REV. A]
• U3017 — Control Module Timer/Clock Performance - Directly related to module timing and often fixed with the same software flash. [Bulletin #1811322, #18-099-16]
• P2281 — Air Leak Between MAF And Throttle Body - Addressed in the same software updates. [Bulletin #1811322, #1807622, #18-099-16, #18-037-16 REV. A]
• P0420 — Catalyst Efficiency Below Threshold - Another code addressed by the software improvements in Ram TSBs for gasoline models. [Bulletin #1805416]
• P026B — Injection Timing Performance - Included in the list of DTCs fixed by a PCM reflash. [Bulletin #1805416, #1807622, #18-037-16 REV. A]

Technical Service Bulletins (TSBs) & Recalls

• 1811322: Mentions U1421 and software enhancements for 2015 models.
• 1805416: Lists U1421 as a code addressed by software updates for 2014 gasoline models.
• 1807622: Cites U1421 and software fixes for 2015 models.
• 18-099-16: A key TSB for 2015 6.7L diesels that lists U1421 as a primary code fixed by an ECM reflash. Also includes improvements for NOx sensors and charging systems.
• 18-037-16 REV. A: Another critical bulletin for 2015 6.7L diesels specifying a software update to resolve U1421, among other codes.

Platform-Specific Known Issues

• Multiple Technical Service Bulletins (TSBs) were issued by Ram to address this specific code via a software update, indicating it was a widespread factory software issue on 2014-2015 models.
• The dual-battery system in diesel models, when one or both batteries begin to weaken, is a very common trigger for an array of electrical faults, with U1421 being a frequent symptom.