How to Fix U1421 Code On Cummins? (Completely Explained)

Diagnostic Trouble Codes, known as DTCs, indicate problems with the car’s engine and supporting components. Detecting the problem quickly with DTC code helps to resolve it faster. Ever wondered what code U1421 means on Cummins?

The code U1421 on Cummins appears when On ECM receives an implausible ignition key off time and sets the code. A defected Body Control Module (BCM),  visible harness from the BCM, loose BCM circuit connection, and a broken PCM module are responsible for the code U1421.

It’s not wise to drive a vehicle with this code. You can solve the issue by determining the signs of the U1421 code.

U1421 Code On Cummins

What Is Code U1421 On Cummins?

In the Cummins, the code U1421 means a situation in the ignition key timing. It is generally an electrical problem.

But breaking the code into small parts will help you understand the issue correctly.

  • U = Electrical network that keeps the electric parts running (in this case, the ignition key cycle)
  • 1 = Fuel and air metering index as per SAE
  • 4 =  Conducive emission control
  • 21 = specific fault index (in this scenario, the implausible key ignition off time)

An imbalanced ignition cycle can’t maintain the ignition timing, which means the implausible ignition key off time, puts the code on the car’s dashboard. It causes some crucial issues in the car. Popping up this code on the car’s dashboard indicates the slow response of the ignition port.

How Serious Is Code U1421 On Cummins?

U1421 on Cummins is not only a severe problem but also a sensitive case. The appearance of this code means the electric parts of the vehicle are in bad condition.

The PCM tracks the off time of a vehicle and compares it to the set value. Even your car’s temperature sensors will stop working because of this code. The real problem begins when the set value doesn’t increase by a little.

In the car’s electrical department, the scenario becomes very messy. You might have to change some essential parts to drive the car peacefully. A disturbed ignition is the worst outcome of this code.

What Causes U1421 Code On Cummins?

There is no exact cause behind the U1421 code. Some potential causes are responsible for the appearance of this code. Ignoring these signs only worsens the situation both for you and your car. So, it’s best to find those causes earlier to solve them efficiently.

Let’s take a quick look at the potential causes behind the U1421 code.

  • A defected body control module (BCM) can’t monitor overall electrical equipment properly.
  • Wet and Exposed Harness Of BCM is unable to hold a strong connection.
  • The weak and loose circuit connection of BCM fails to deliver signs in time.
  • The broken Powertrain Control Module (PCM) can’t provide the required electrical power.
  • A problematic cluster module also causes the U1421 code on Cummins.

How To Fix Cummins U1421 Code?

Fixing the U1421 code on Cummins is not child’s play. It’s a very complex and sensitive problem.

However, checking out the probable cause yourself might solve the U1421 code. But experts handling this problem are the best solution.

Follow these methods to solve this code DIY:

Fix The Harness

Look for a loose harness connection in the BCM. Connect it to the BCM as soon as you find it.Sometimes fixing the leakage in the wires of the circuit connection solves the U1421 code. It’s better to replace the wire with a new one.

Scanning The Code

Expert mechanics use an OBD-II scanner to scan the U1421 code. Scanning helps to crack the implausible ignition off time issue faster.

Restoring The PCM

Well, it’s super hard to restore the car’s PCM. But, it can be done. If you’re lucky,  fixing the loose hose connection resolves the U1421 code. Don’t fix it yourself if you’re an amateur. Ask for experienced mechanics’ help.

Other Symptoms Of Getting U1421 Code On Cummins

You’ll hardly notice any symptoms before the code U1421 pops up on your car’s dashboard. But some signs can be detected if you’ve sharp eyes.

Another problem is that these symptoms are identical to other DTC codes. Find a better and more experienced expert to inspect those symptoms thoroughly.

Let’s find out these symptoms of the U1421 code.

  • Engine Light Running for a long time is a common indicator of the U1421 code.
  • Service Engine Warning Light means the engine is misfiring
  • The car’s control panel indicates the lights while driving.

How Much Does It Cost To Fix Cummins U1421 Code?

The fixing cost of the Cummins U1421 code depends on some factors. Different auto repair shops charge differently depending on their expertise. Some repair shops charge extra money to run a diagnosis.

Labor charges also change if the location is different. Then comes your car’s make and model. The fixing cost even varies depending on the engine type.

Most automotive repair shops charge hourly. The average per hour rate is between 75 to 150 bucks per hour.

It’ll cost you even more if you take your car to a famous mechanic’s shop will cost you even more. They charge more because of the complex structure of the vehicle. This makes code scanning hard for the mechanic. But they’ll fix the problem no matter how serious it is.

Can You Drive With Your Cummins With Code U1421?  

This question has a technical answer. You can and can’t drive with code U1421 on your Cummins. We recommend you not to drive if you notice this code.

A loose hose connection to PCM isn’t able to deliver the electric signal to the BCM. Power cut may occur at any time because of this issue. As a consequence, the car will stop at any time.

It’s bad news if the circuit combination is not in place. The car’s electric parts, like lights, will stop working.

There’s a chance of the signal light going out while driving. You’ll be in deep trouble while driving if the car’s BCM is broken.


The DTC code U1421 is not a simple car problem like other DTC codes. Solving this code is tricky but possible. You won’t have to pay hourly to fix the code if you can detect the signs early.

Hopefully, analyzing what code U1421 means on Cummins has helped you fix the issue accurately. Scrutinize the causes before you take any step.

A regular check-up keeps the vehicle safe from these terrible DTC codes. Don’t forget to take an expert’s help to solve the U1421 code faster!

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