P0291 OBD Error Code: Problem & Solutions

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The “drivers” or special transistors in the Engine Control Module (PCM) turn the fuel injectors on and off in the Fuel Injection System. If the PCM is unable to control the fuel injector, the error code P0291 will get generated.

If the drivers in the PCM are unable to control the Fuel Injector, this might result in the fuel injector spray to get reduced from the prescribed limits. This will result in a lean mixture hence beginning a ripple. The oxygen sensor will then send signals to the PCM indicating a lean mixture. This will, in response, lead to enrichment of fuel mixture being delivered to all the cylinders. Thus, the fuel economy will plummet.

The conditions in which the error code is generated:

• Fuel injector is defective
• Electrical wiring is loose
• There’s corrosion on the electrical wiring
• Connector faces are damaged

The OBD code P0291 indicates that the PCM is unable to control the fuel injector. Some of the parts might be causing this and thus must be repaired or replaced immediately to eliminate the error code. Some of these parts might be:

1. Fuel Injector - The ECM sends a signal to the fuel injector to spray the pressurised fuel into the engine. The fuel delivered will depend on the duration of time the fuel injector is open. If there is an issue with the Fuel Injector itself, the PCM will not be able to control it and thus the fuel mix might be tainted and delivery could be below/above the prescribed limits. Thus, it is necessary the fuel injector is repaired or replaced, as required, urgently.
2. Fuel Injection System - For smooth working, an engine needs to be supplied with the right amount of fuel/air mixture. Due to an issue with the Fuel Injection system, the amount of fuel delivered to the engine might be exceeding or be below the optimum limits or the balance of quantities between the fuel and air might not be in concurrence with the limits required for an efficient emission.
3. Wiring - The Fuel Injection Wiring/Harness includes the wiring of the fuel injector. If the wiring is faulty, it might be leading to short circuiting or variations in the amount of current flowing to the injection system. Fixing the wiring is a tedious job since it requires looking very minutely to any rust or cracks in the wiring or harness.
4. Connector - The Fuel Injection Connectors are used for making connections between the incoming current to the Fuel Injector and the ECM. The problems with Fuel Injector Connectors usually go undiagnosed and lead to repairs of costlier parts without the actual problem getting solved. The connectors can be replaced at very cheap prices and thus if the error code is being generated, it might be wise to have a look at the connectors early on so that the problem can be diagnosed and you don’t have to waste thousands of dollars repairing/replacing parts that actually are not the problem at all.
5. Powertrain Control Module - PCM is a combined control unit that consists of Engine control unit (ECU) and Transmission control unit (TCU). The PCM is one of the most important components in the control system of a vehicle. It controls over a hundred factors in a vehicle. The PCM is commonly referred to as ‘The Brain’ of the engine control system. Thus, being pivotal in the operations of a vehicle, it is extremely necessary that even the slightest fault in the PCM must be immediately rectified.
6. Engine Control Module - The Engine control module controls the fuel mixture, ignition timing, variable cam timing and the emission control. It acts as the main think tank and a controlling body of the engine management system. It is as essential as a brain is to the human body and thus must be fixed immediately in case of any issues detected.

If the PCM is unable to control the Fuel Injector and thus, as a result, the fuel air mixture going in is lean, there are some symptoms that might start showing and hence point in the right direction. These symptoms might be:

• Engine light or Service Engine Soon Warning Light might be ON
• Engine light misfire
• Engine might be running rough
• MPG might be low

To correct the issues occurring with the Cylinder 11 Injector Circuit, you can follow the below steps:

• Replacement of the bad injector
• Cleaning out the Fuel Injector
• Replacement or Repairing of the fuel injector electrical connector

Electrical connections can become corroded over time due to all sorts of reasons or they might get loose and keep working correctly.

The mechanic will first use an OBD II scanner to get a reading on the codes that have been stored by the PCM. For error code P0291 issue, the mechanic might use an Ohmmeter, noid lamp and the vehicle’s user manual to figure the severity of the problem.

Once the issue is confirmed, the mechanic will most probably examine the associated connectors and wirings and also fuses, if it’s necessary. All the while, the system should be reset to see if the codes have permanently been eliminated or if they come back.

Common Mistakes When Diagnosing the P0291 Code

Diagnosis of error code P0291 might give inaccurate results if the following mistakes have occured:

• There might be Fuel Injection Control Module (FICM) failure
• There might be Fuel Injector Failure
• PCM might have failed
• There might be some wiring issue