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P2605 Intake Air Heater B Circuit Open

OBD-II Trouble Code Technical Description

Article by
John Ingalls
John Ingalls
Former Service Manager & Air Force Mechanic

Intake Air Heater "B" Circuit Open

What does that mean?

This generic powertrain diagnostic trouble code (DTC) typically applies 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 a number of possible codes that are associated with an intake air heater circuit "B" malfunction. An intake air heater is an essential component for a diesel engine to assist the starting process. The four codes that the Powertrain Control Module (PCM) may set for intake air heater "B" circuit issues are 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 incorporates a heater element, relays, temperature sensor and at least one blower. Air ducts are also needed to route the warm air to the intake and electrical connections and wiring control the operation of these components.

Trouble code P2605 is triggered by the PCM when it detects an open circuit in the intake air heater "B" circuit. Refer to a vehicle specific repair manual to determine which is the "B" circuit for your particular vehicle.

Here is an example of an air intake heater:
Air intake heater

Code Severity & Symptoms

The severity of this code is normally moderate, but can be severe based on the specific malfunction.

Symptoms of a P2605 diagnostic trouble code may include:


Typically, potential causes for this code include:

Another style of air intake heater:
GM 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 circumstances this can save a lot of time in the long run by pointing you in the right direction.

The intake air heating circuit might not work automatically if the ambient air or engine temperature is above the limit set by the manufacturer. The circuit should activate if it is commanded "ON" with a scanner, or if power is applied manually.

Basic Steps

Advanced Steps

Advanced steps become very vehicle specific and require the appropriate advanced equipment to perform accurately. These procedures require a digital multi meter and the specific technical references for the vehicle. Voltage requirements will very based of the specific year, model and the 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 to point you in the right direction to correct 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.

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