Fuel system 1 OL fault – What Causes & How to Fix It?

An open loop (OL) fault is an electrical problem that occurs when a system fails to close its calculated circuit due to an interruption. These interruptions prevent the control system from getting the necessary feedback, such as emission, engine performance, sensor reading, etc., to make important adjustments. The result is poor engine performance and other issues.

Particularly, OL fault arises when components such as sensors and wirings responsible for sending these feedbacks to the ECM are faulty. Finding the cause of this issue and fixing it is paramount if you want your car to function optimally. With an understanding of what an OL means, let’s look at what fuel system 1 OL fault is, what causes it, and how to fix it.

how to fix fuel system 1 ol fault

What is a fuel system 1 OL fault?

The fuel system 1 OL fault occurs when the control system does not switch from an open to a closed loop as the engine temperature rises, preventing the system from making correct fuel adjustments and causing your engine to run rich.

Before the engine warms up, it depends on data from various sensors, such as the ECT, MAF, and MAP to decide how much fuel to push into the engine for optimal performance. At this stage, the engine runs on an open loop, which is normal.

However, when the engine warms up and the oxygen sensors get activated, the ECM then switches to relying on the O2 sensors to make necessary fuel adjustments. At this stage, the system should start running on a closed loop.

However, once this switch does not occur, the system continues running on an open loop and shoves excess fuel into the engine. A car running on an open loop is one unable to get the necessary feedback from various sensors or components to make needed adjustments, invariably causing performance issues.

So if you detect a fuel system 1 OL fault in Nissan or any other model, the wise thing to do is fix it as soon as possible. But this is possible when the cause of the fault is known.

Causes of fuel system 1 OL fault

The fuel system 1 OL fault in Ford Focus and other models arises when various components responsible for feeding the ECM with information to make timely adjustments are bad. These include faulty wiring, O2 sensors, MAF sensors, etc

Faulty oxygen (O2) sensors

Dirty or bad O2 sensors are one of the most common causes of open-loop faults, whether in fuel systems 1 or 2. Oxygen sensors help measure the amount of oxygen in the exhaust and communicate this to the engine computer. The ECM then uses this information to determine how much fuel to push into the engine.

However, when the O2 sensor is faulty and unable to do this effectively, the ECM fails to switch into a closed loop due to a lack of feedback. Failure to switch causes the ECM to make wrong fuel adjustments. This not only hampers vehicle performance but causes increased fuel consumption.

Faulty wiring

Another common cause of fuel system 1 OL fault in Chevy Cruze and other vehicles is bad wiring. Wires serve as a link between the sensors, actuators, and control systems. However, when they get bad, loosed, or damaged, it causes an interruption in the transmission signal between these components. This invariably results in an open loop since the ECM is unable to get feedback from them.

Bad engine control module (ECM)

A vehicle’s control module is responsible for generating control signals based on feedback received, as well as managing a car’s electrical system. However, it can get faulty due to electrical, software, and other issues within the module. When the control module gets bad, it not only fails to interpret data accurately, but it also hampers the creation of control signal—invariably causing an open loop.

Bad MAF or ECT sensor

The mass air flow sensor and engine coolant temperature sensor are two essential sensors that help your car perform well. With the MAF sensor helping to measure the amount of air entering the engine, the ECT helps measure engine coolant temperature.

The ECM, in turn, uses input from these sensors to adjust fuel injection and ignition timing. If either of these sensors fails and provides wrong readings, the ECM cannot switch to close loop. Engine running on an open loop control due to Bad ECT or MAF not only results in misfires but generally causes your car to run poorly.

Wrong grounding or voltage level

Generally, grounding helps prevent sudden surges and shocks. However, poor grounding results in the creation of wrong current pathways affecting the current distribution within the system. In the same vein, too high or too low voltage level impedes the correct flow of current within the circuit. Because correct current distribution is impacted, an open loop situation occurs.

Poor insulation

The insulation on your car’s wiring can get damaged due to age or other issues. This often results in short-circuiting and eventually causing the fuel system 1 OL fault in your Nissan or Ford.

Bad actuators

The ECM uses actuators such as motors, solenoids, and valves to carry out visible actions. If any of these actuators fails or gets stuck in a particular position, they interrupt the system’s operation.

For example, when the fuel injector fails or gets stuck in the open position, it injects too much fuel into the engine. This not only deters vehicle performance but also results in poor fuel economy.

Faulty components

Faulty components, such as semiconductors, can result in poor connections, hampering the proper flow of current. With interruption in connection, an open-loop situation can occur.

How to diagnose fuel system 1 OL fault

Cars not switching from close to open loop is a telltale sign of an open loop fault. Unfortunately, diagnosing a fuel system 1 OL fault in a Ford and other vehicles is tricky since various factors could be responsible for this fault. Hence, such a diagnosis is best left to experts. However, if you want to do it yourself, note this.

Generally, when there is an OL fault, the system displays an error message reading “OL.” Your engine check light will also turn on. More so, fuel system 1 open loop fault cause misfire, stalling, loss of engine power, and other car problems. While these point to an OL fault, they don’t point to specific components responsible for the OL fault. Hence, the need for a diagnostic test.

Plug any diagnostic tool into your car’s OBD II port and scan for error codes. The error codes will help you determine which component is causing the fault. This implies you must know how to read these codes when they appear. If you can’t, look up your OBD codes booklet to interpret those codes.

You can also read live data during the scan test. Usually, technicians can compare these real-time data to the estimated ones and can pinpoint the cause of the OL fault.

How to fix a fuel system 1 OL fault

Just like diagnosing, fixing is a bit tricky, too, since anything can be responsible. However, if you have made a proper diagnosis, here is how to fix fuel system 1 OL fault in any car. Note that which of these you do will depend on the fault codes in your OBD II scanner.

Change bad sensors

Suppose the diagnosis points to any sensor as the cause of OL fault; replacing it should solve the issue. However, first, check the specific sensor to be sure it is really faulty and why. If it is dirty, you can clean otherwise, replace it with one compatible with your vehicle make and model.

Repair faulty actuators

If actuators cause the fuel system 1 OL fault in your Chevy Silverado or your specific vehicle, check to see why they got bad. Check for broken parts, if they got stuck or have any mechanical issues.

Depending on your findings, repair or replace with one compatible with your car’s make and model. More importantly, ensure the new actuators are correctly installed and adjusted.

Replace faulty wiring and connections.

Inspect the wires and connections in the system. Check for tear, corrosion, or looseness. If they are bad, replace them so your signals can be restored. Also, check the wiring harness of any faulty components the scanner reveals. If these components are defective, chances are their wires or connectors are also worn.

Replace any other defective components.

Make repairs and replacements based on the result of your diagnosis. So long as these things are fixed, the open-loop fault should disappear.

However, while doing these yourself is okay, try taking your car to an expert to run a check afterward to ensure everything is in place. Lastly, if you are unsure how to diagnose and fix it, leave it to the hands of professionals to prevent more damage that may cause you to spend more.


Generally, the OL should display when the car is cold and switch to CL when it warms up. But if there is an open loop fault, it will fail to change to CL even when the vehicle temperature rises. However, after fixing the components responsible for the OL fault, the OL error code displayed on your dash should disappear whenever your vehicle is warm. But note that these things can be tricky.

The error code may leave and return after a while. So to ensure these components responsible for the fuel system 1 OL-fault in your BMW, Ford, or any other vehicle are fixed, do the following.

Troubleshoot the fuel, air, and spark. Check your fuel consumption; it should be better or at least return to the usual. Check your air-fuel ratio; you can do this by looking at the oxygen data sensor from the ECU. Better still, use an air-fuel ratio gauge. Has the ratio returned to normal?

You should also check how well the car runs. Rough running at idle that worsens when you apply more throttle may mean one of the components responsible for the fault wasn’t fixed well.

Start your engine and record how fast it turns on. If it stalls for long before coming up, chances are there are still issues causing the ECU to push more fuel into the engine, causing the engine to run rich. If the engine runs rich, check the oxygen sensors, MAF sensors, and fuel injectors again. 

If all these look good, the ECM is likely supplying just the right amount of fuel to the engine. This means that various actuators and oxygen sensors are now working fine.

Safety precautions

While fixing the fuel system 1 OL fault may seem simple, it requires expertise and carefulness. Hence, you may end up causing damage not to your car but to your body. To avoid these, here are safety precautions to follow.

  • Be sure you can fix replacement sensors and any defective components. If you can’t, refer to an expert to prevent unnecessary cost
  • Do not make repairs based on guessing; you will spend more. Always make diagnosis
  • Replace with only compatible sensors or parts.
  • Work in a ventilated area, especially if you’re using chemicals like grease to avoid suffocation or respiratory issues.
  • If there is a need to lift your car, use suitable jacks and support with a Jack stand
  • Wear safety gear (gloves, safety Google), especially when cleaning parts with detergents like carb cleaners and their alternatives.
  • Always remove the battery terminals before removing any electrical wires or connectors to avoid shock.

Final Words

The Fuel System 1 OL fault pops due to ECM not switching to a close loop due to a defect in components responsible for sending feedback to the engine computer. When this happens, you should get an OL error code on your dash even if the engine is warm.

The first place to start is to scan for error codes so you find the real culprit. Trying to fix different components by guessing and hoping you fix the real culprit is not cost-effective. With the codes, fix the issue and finally carry out subsequent tests so you’re sure that the fault has been fixed.

Osuagwu Solomon

Osuagwu Solomon is a certified mechanic with over a decade of experience in the mechanic garage, and he has over five years of experience in the writing industry. He started writing automotive articles to share his garage experience with car enthusiasts and armature mechanics. If he is not in the garage fixing challenging mechanical problems, he is writing automotive repair guides, buyer’s guides, and car and tools comparisons.

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