P2604 Intake Air Heater “A” Circuit Range/Performance

Technical Description of OBD-II Trouble Code

The circuit range/performance of the intake air heater “A” is being affected.

What does that signify?

This generic powertrain diagnostic trouble code (DTC) is applicable to all OBD-II equipped vehicles that have an air intake heater, including but not limited to Chevrolet GMC (Duramax), Ford (Powerstroke), Honda, Nissan, Dodge, etc.

This code is one of several possible codes associated with a malfunction in the intake air heater circuit. An intake air heater is a crucial component for assisting the starting process of a diesel engine. The Powertrain Control Module (PCM) may set five codes for issues with the intake air heater “A” circuit: P0540, P0541, P0542, P0543, and P2604.

What is the purpose of an air intake heater?

The intake air heater “A” circuit is designed to operate components that provide warm air to facilitate diesel engine starting and idling at different temperatures. The typical intake air heater circuit includes a heater element, relays, temperature sensor, and at least one blower. Air ducts are also necessary to direct the warm air to the intake, and electrical connections and wiring control the operation of these components.

The PCM triggers trouble code P2604 when it detects that the intake air heater “A” circuit is out of range or experiencing performance issues. The circuit may be out of range, contain a faulty component, or have improper airflow. Various malfunctions within the circuit can be physical, mechanical, or electrical in nature.

Here is an example of an air intake heater:

Code Severity & Symptoms

This code is typically of moderate severity, but it can be severe depending on the specific malfunction.

Symptoms of a P2604 diagnostic trouble code may include:

Causes

Potential causes for this code typically include:

Another style of air intake heater:

What are the most common repairs?

Diagnostic and Repair Procedures

The first step in the troubleshooting process for any malfunction is to research the Technical Service Bulletins (TSB) for the specific vehicle by year, model, and power plant. In some cases, this can save a significant amount of time by providing guidance in the right direction.

The intake air heating circuit may not work automatically if the ambient air or engine temperature exceeds the limit set by the manufacturer. The circuit should activate if it is commanded “ON” with a scanner or if power is manually applied.

Basic Steps

Advanced Steps

Advanced steps are highly specific to the vehicle and require the appropriate advanced equipment for accurate performance. These procedures necessitate a digital multimeter and the specific technical references for the vehicle. Voltage requirements will vary based on the specific year, model, and diesel engine of the vehicle.

Specific Checks:

Note: On applications that have Mass Airflow sensors, the intake air temperature sensor is incorporated into the sensor body. Consult technical data to determine the correct pins associated with the sensor.

Specific checks must be performed using the troubleshooting guidelines for the specific vehicle, utilizing the technical manual or online reference material. These steps will guide you through the process of checking the power and ground to each component within the intake air heater circuit in the proper sequence. If the voltage is correct for a component that is not functioning, that component is likely defective and requires replacement. If power is not available to operate the circuit, continuity checks may be necessary to identify faulty wiring or components.

Hopefully, the information in this article has been helpful in directing you towards resolving the problem with your intake air heater circuit malfunction. This article is strictly informational, and the specific technical data and service bulletins for your vehicle should always take priority.