Skip the auto shop - Our mechanics make house calls

P0648 OBD-II Trouble Code: Immobilizer Lamp Control Circuit

Check Engine Light

P0648 code definition

When there is a fault in the immobilizer lamp control circuit, a P0648 trouble code is stored in the Powertrain Control Module (PCM) and the Check Engine Light illuminates. The problem could happen if the PCM or another supporting control module detects a fault. Supporting control modules include the alternative fuel control module, anti-lock brake control module, anti-theft control module, body control module, climate control module, cruise control module, fuel injection control module, instrument panel control module, proximity alert module, traction control module, and turbo control module, among others.

What the P0648 code means

A P0648 trouble code means that the PCM or other control module has detected an abnormal reading in the immobilizer lamp control circuit. Vehicle owners should keep in mind that illumination of the Check Engine light might require multiple drive cycles, sometimes even up to eight.

What causes the P0648 code?

A defective immobilizer lamp bulb or circuit is usually the culprit behind a stored P0648 trouble code. Some other causes for the storage of this code include corroded, shorted, or damaged wiring, connectors, and components within the Controller Area Network (CAN) Bus harness; a defective CAN Bus; or a loose ground strap or broken wire on one of the control modules.

What are the symptoms of the P0648 code?

Symptoms typical of a P0648 trouble code include illumination or flashing of the immobilizer lamp in addition to an illuminated Check Engine Light. If the Check Engine Light is not illuminated, the code is still stored, but shown as pending.

How does a mechanic diagnose the P0648 code?

Diagnosing a P0648 trouble code requires the use of a digital volt/ohmmeter and an advanced scanner by the mechanic, in addition to the mechanic following these steps:

  • Visually checking all wiring, components, and connectors for damage

  • Downloading all stored trouble codes and freeze frame data from the PCM for help in diagnosing the source of the problem

  • After replacing any wiring, connectors, or components, clearing the code and test driving the vehicle

  • If the code returns, inspecting the pins of the CAN Bus with a specialized scanner to determine where the fault is originating from. Before testing the CAN Bus pins, the mechanic needs to install a memory saving device to keep the PCM and other control modules from losing their memory.

  • The mechanic can also disconnect all of the control modules and perform a circuit continuity test using the volt ohmmeter, though this process is time consuming and cost prohibitive.

  • If the mechanic wishes to proceed, they should test continuity between each control module and the battery ground. If so, the mechanic should use an auxiliary ground cable to diagnose any ground discrepancies.

  • Using a CAN Bus wiring diagram, use the volt/ohmmeter to test the connection between each control module connector.

  • Clearing the P0648 trouble code and test driving the vehicle to see if it is stored once again.

Common mistakes when diagnosing the P0648 code

The most common mistake made by mechanics when diagnosing a P0648 trouble code is to treat any codes stored in reaction to the communication failure between the immobilizer lamp circuit and the PCM or other control module. In effect, this treats the symptoms but not the problem, with the trouble code returning.

How serious is the P0648 code?

A P0648 trouble code can affect a variety of control modules, causing issues with communication between the control modules and the PCM. The vehicle can still operate with a P0648 trouble code stored as it is just an indicator of a communication problem between control modules. Mechanics should focus on fixing the faulty control modules, wiring, or connectors to see if that alleviates the problem first.

What repairs can fix the P0648 code?

To repair a P0648 trouble code, a mechanic should perform the following repairs:

Need help with a P0648 code?

YourMechanic offers certified mobile mechanics who will come to your home or office to diagnose and repair your vehicle. Get a quote and book an appointment online or speak to a service advisor at 1-800-701-6230.

The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

Skip the repair shop, our top-rated mechanics come to you.

At your home or office

Choose from 600+ repair, maintenance & diagnostic services. Our top-rated mechanics bring all parts & tools to your location.

Fair & transparent pricing

See labor & parts costs upfront, so you can book with confidence.

12-month, 12,000-mile warranty

Our services are backed by a 12-month, 12,000-mile warranty for your peace of mind.

Get A Quote

Ask a Mechanic
(100% Free)

Have a car question? Get free advice from our top-rated mechanics.

Ask A Mechanic
Over 10,000 questions answered!

Need Help With Your Car?

Our certified mobile mechanics make house calls in over 2,000 U.S. cities. Fast, free online quotes for your car repair.


Post a question and get free advice from our certified mechanics.


More related articles

Rules of the Road For Iowa Drivers
Driving on the roads requires knowledge of the rules, many of which are based on common sense and courtesy. However, even though you know the rules in...
How to Avoid Back Pain in a Car
If you have back problems, sitting in a car for an extended period of time can be excruciating. Even without back problems, you could experience discomfort and soreness from...
P2422 OBD-II Trouble Code: Evaporative Emissions Control System (EVAP) Vent Valve Stuck Closed
Diagnostic Trouble Code (DTC): P2422 P2422 code definition Evaporative Emissions Control System (EVAP) Vent Valve Stuck Closed Related Trouble Codes: P2441: EVAP Vent Valve Stuck Open EVAP trouble...

Related questions

Q: Car is misfiring and has a lack of power

It is very difficult to definitively say what the issue is. Have you had the vehicle scanned for diagnostic troubleshooting codes? If not, you should start there. Due to your vehicle being pre-1996, the method of receiving codes will be...

Q: check engine light is on -- ge -ot a diagnotics test from onstar -- test stated emmissions system issue whatdoes this mean

Hello, thanks for writing in about your Chevrolet Malibu. If they did not give you the trouble code that is stored then you are going to need to have the system tested to see if the code can be diagnosed...

Q: No throttle response on 2012 dodge avenger

In the future, please include the motor size. Thanks. Your electronic throttle system consists of the throttle pedal assembly with an accelerator pedal position sensor, the throttle body which consist of a TPS (Throttle Position Sensor), throttle plate actuator,...