P2608 Intake Air Heater “B” Circuit High

Technical Description of OBD-II Trouble Code

The circuit for the intake air heater “B” is experiencing high levels of activity.

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 “B”. An intake air heater is a crucial component for a diesel engine as it aids in the starting process. The Powertrain Control Module (PCM) may set four codes for intake air heater “B” circuit issues: P2605, P2606, P2607, and P2608.

What is the purpose of an air intake heater?

The intake air heater “B” circuit is designed to operate the components that provide warm air to facilitate diesel engine starting and idling at various temperatures. The typical intake air heater circuit consists of 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 P2608 when it detects a high signal from the intake air heater “B” circuit. The circuit may be out of range, contain a faulty component, or have improper airflow. Various malfunctions within the circuit may be present and can be physical, mechanical, or electrical. Consult a vehicle-specific repair manual to determine which circuit corresponds to “B” in your particular vehicle.

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 P2608 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 function automatically if the ambient air or engine temperature exceeds the manufacturer’s limit. 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 in 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 using 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 to a component that is not functioning, that component is most likely defective and requires replacement. If power is not available to operate the circuit, continuity checks may be needed 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.