How to Fix the P1688 DTC Code on Cummins (Expert Solutions)

The DTC (diagnostic trouble code) notifies the owner about the specific issue with the vehicle. P1688 is one such DTC that appears anytime while the engine is on. If you have Cummins and are familiar with the code, you probably know how to deal with it.

Conversely, if the code is entirely new to you, you’d better approach the code by knowing its meaning. In simple language, Code P1688 On Cummins indicates a failure in the internal fuel injection pump controller.

Well, this is a pretty short answer to the question. Our purpose is to give you general guidelines on how to fix the code while the symptoms, causes, and severity will also be taken care of. Keep reading!

How to Fix the P1688 DTC Code on Cummins

What Does Code P1688 Mean On Cummins?

We have previously mentioned that the code P1688 indicates a failure in the internal fuel injection pump controller. The code is set, especially if there is damage to the pump, any programming error, or maybe an error in the PCM( powertrain control module) memory. 

When the Fuel Pump Control Module (FPCM) is monitored, ensure the ignition is on, but the engine is off. When the code appears, you must take the necessary steps to fix it. Here is a breakdown of the code P20b9 to increase your understanding.

  • P= denotes the vehicle’s powertrain. 
  • 1= indicates a generic number derived from the SAE standard.
  • 6= refers to the internal fuel injection pump controller
  • 88= indicates a failure of the internal fuel injection pump controller

How Serious Code P1688 On A Cummins?

How Serious Code P1688 On A Cummins?

The fuel pump is a very important part of the fuel system. The other parts include injectors and pressure regulators. If any of these parts have any issue, there can be serious drivability, including the vehicle won’t start.

Problems with the fuel pump may prevent the engine from starting. The performance of the engine will be reduced. This is obvious since a faulty fuel pump may change the timing of the injection or cause an imbalance in the air-fuel ratio.

There can be additional consequences too. Fuel efficiency may be reduced. All in all, a faulty fuel pump will affect the overall performance of the vehicle with the Cummins engine.

What Causes Code P1688 On A Cummins?

A poor electrical connection could be the major reason for the code. There could be some other additional causes. If you can address and resolve these causes, it will certainly result in the code being removed.

  • Electrical Fault 
  • Wear and tear 
  • If the dirt or moisture contaminates the fuel
  • Damaged or poor electrical connection
  • The circuit has a poor electrical connection
  • The trip counter is equal to zero
  • Faulty fuel pump controller

Other Symptoms of Getting Code P1688 on Cummins

There is a possibility that fuel pump failure often occurs without symptoms. The most obvious symptom is that you will have an illuminated check engine light. The other symptoms include the following:

  • Due to wear in the internal component, noise from the pump
  • Unable to start the engine 
  • Lack of power when the engine is loaded
  • Reduction in the fuel flow at the inlet and outlet valves
  • Corroded Diaphragm springs
  • Reduction in fuel pressure and fuel delivery pressure

How To Fix the Code P1688 On Cummins?

P1688  should be taken seriously and fixed without wasting too much time. You can fix the code by following the DIY (do it yourself) approach.  Or take professional help? It is a logical decision to get help from an expert with experience in this field. 


When it comes to diagnosis, if you follow the DIY( do it yourself) approach, you will need a repair service bulletin from Cummins corresponding to the make, year, and engine size. 


The fixing strategy we will describe below is for informational purposes only. The fixing strategy may change corresponding to the make, year, and engine size. 

Basic Tools Required

Fixing the code requires a few common and necessary tools, which include the following:

  • The OBD Scanner 
  • A digital Volt or ohmmeter 
  • Screwdrivers and pliers

Step 1: Collect all the stored Data 

Usually, the first thing mechanics do: they collect all the freeze frame data using an OBD scanner. Then they clear all the codes and test drive the vehicle. After the test drive, they rescan and see if any codes return. 

If the code P1688 returns, they find the possible causes for the code. It can either be a fuel injector or an FCPM. Anyway, move on to the next step.

Step 2: Visual Inspection

Visual Inspection

A code may appear due to damaged wiring and poor electrical connection. So, locating the damaged wire and replacing it with a new wire may fix the code in no time. 

Mechanics usually inspect all the parts and wiring harness around the fuel pump and pump injector. If everything is fine here, move on to the next step.

Step 3: Resistant Test

Resistant Test

Whether the proper voltage is maintained, it is crucial to check the voltage range. Mechanics do check voltage using a digital volt or ohmmeter. The voltage should not be less than the predetermined range.

Some repairs may fix the issue.

The code may disappear if the issue is fixed. During the process, you may need to replace parts and components given below:

  • Fuel pressure Control module FPCM
  • replace the fuel injection pump
  • Fuel Pressure Gauge 
  • Corroded Electric wire

How Much Does It Cost To Fix Code P1688 On Cummins?

When it comes to the cost of fixing the code, there are three important criteria you have to think about. The first is a professional’s cost, usually given per hour. The cost of hiring a professional for an hour is somewhere between $100 and $150.

On the other hand, you need a skill set and tools such as a scanner or ohmmeter to fix the issue on your own. The cost of purchasing them will be somewhere between  $200 and $300.

Finally, besides some hidden costs, including tips or VAT, or maybe transportation costs, you may also have to bear the cost of replacing parts, especially the fuel pump control module.

Can You Drive With the Code P1688 On Cummins?

As you have learned, the severity of the code A faulty fuel pump control module prevents you from starting the vehicle. Sometimes, partial faults like leaks may not stop you from driving, but you should not drive. As soon as the code appears, take the necessary steps before it is too late.


The problem with this DTC is that it can often appear without warning signs or symptoms.  Act intelligently when the P1688 comes on the screen. Some people freak out, which must be avoided.

The best way to approach the code is first to get the meaning of the code and then identify the root cause behind the code. As soon as you have the reason, simply fix it.

People frequently ask, “Can I do it myself?”  Well, you know the answer. Without experience and skill, it is advised to seek a professional with previous experience in this field.

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