|Trouble Code||Fault Location||Probable Cause|
|P1259||Immobilizer to PCM Signal Error (Ford)
VTEC System Malfunction (Acura, Honda)
Glow Plug Module Control Over Current (Chrysler/Dodge/Jeep)
Engine Coolant System Valve Short to Ground (Volkswagen/Audi/Volvo)
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What Does Code P1259 Mean?
SPECIAL NOTES: Since the purpose of anti-theft systems is to prevent vehicle theft, there is no DIY repair information available for immobilizer related faults, beyond a few simple checks that may or may not resolve the problem. Unlike other faults in the CAN (Controller Area Network) system for which comprehensive repair information is available, factory-fitted anti-theft systems are protected by captive technology/information, which means that only authorized dealers of a vehicle has the software and equipment to diagnose the root cause(s) of immobilizer related faults.
The only other persons that may have access to the relevant software and equipment are some locksmiths who have gone to the trouble and huge expense to become trained, vetted, accredited, and bonded, meaning that apart from authorized dealers, there are very few people who can legally diagnose and repair this code. END OF SPECIAL NOTES.
OBD II fault code P1259 is manufacturer-specific code that some manufacturers define as “Immobilizer to PCM Signal Error”. On applications that use this definition, code P1259 is set when a break in communication between the immobilizer module and the PCM (Powertrain Control Module), or between the transponder key and immobilizer module occurs.
Immobilizing, or anti-theft systems go by many names, such as General Motors’ VDT (Vehicle Theft Deterrent) system, Fords’ PATS (Passive Anti-theft) system, or Chryslers’ SKIS (Sentry Key Immobilizer) system. Regardless of the name however, all anti-theft systems have the sole purpose of preventing a vehicle being stolen, but when a loss of communication occurs between the PCM and the immobilizer module, there are no easy cures, even for the legal owner of the vehicle.
In simple terms, most applications work on the principle of a transponder receiver that “reads” the security code transmitted by a coded chip in the key. When the transponder receiver (that is wired into the PCM) does not recognize the code sent by the key, or does not receive any communication from the key, the immobilizer module continues to disable the ignition, starter, and/or fuel management circuits in the PCM.
In practical terms, the immobilizer module needs to recognize, and acknowledge that it recognizes the code transmitted by the key via the transponder before it can enable the PCM to activate disabled ignition and fuel management circuits.
The image below shows the battery in a typical transponder key being replaced. Note that designs of key fobs and battery replacement procedures vary greatly between applications.
What are the common causes of code P1259?
The most common cause of code P1259 is flat batteries in keys, with abnormal system voltages caused by faults and defects in the charging system that could damage control modules following close behind. Other possible cause could include the following-
- Open circuits in the CAN system
- Damaged, burnt, shorted, or corroded wiring and connectors
- Loss of ground to some modules
- Defective immobilizer modules. Note that this is a relatively rare event, but not altogether impossible.
- Defective electronics and/or programming errors in the key, fob, or keyless entry system
- Failed, or defective aftermarket immobilizer bypass devices.
- Failed, or failing PCM. Note that this is also a rare event, and the fault must be sought elsewhere before any controller is replaced.
What are the symptoms of code P1259?
One symptom shared by all applications is that the vehicle won’t start, although in some cases, the engine may still crank. Other possible symptoms could include the following-
- Flashing security-system related warning lights.
- In some cases, the engine may switch off a few seconds after starting.
- In cases where intermittent faults in the wiring cause a momentary loss of communication, the engine may shut off or stall unexpectedly. This will be accompanied by security-system related warning lights.
- Intermittent faults can cause unpredictable no-start conditions, which will also be accompanied by security-system related warning lights.
How do you troubleshoot code P1259?
NOTE: Diagnosing immobilizer related faults is NOT recommended for non-professional mechanics, or even professional independent mechanics that do not have access to factory diagnostic equipment and software. Modern anti-theft systems are protected by several layers of built-in deterrents to prevent tampering that could cause a vehicle to be “hot-wired”. Moreover, only factory-approved diagnostic equipment has the ability to extract fault data from the security system, which means that there is little, to nothing non-dealer technicians can do to trace, diagnose, and repair immobilizer related codes beyond the few steps outlined below. Be aware though that replacing transponder key batteries is not guaranteed to resolve code P1259.
Record all codes present, as well as all available freeze frame data. This information can be helpful should an intermittent fault be diagnosed later on.
NOTE: It is important to confirm or verify that the code actually is associated with the anti-theft system, since there are many other causes of no-start conditions. Check, and verify that illuminated warning lights (that could either flash or burn steadily) actually indicate a security system issue. Refer to the “Related Codes” section of this guide for other possible definitions of code P1259.
Since all immobilizer, systems require a power source to transmit the code from the key or fob to the immobilizer module, replace the battery in the key, but be sure to refer to the directions in the manual for the correct procedure to prevent damage to the key.
Test the system by starting the vehicle to see if the battery replacement resolved the problem, but if the code persists, it is likely that the key or fob had lost some, or all of its programming. There is no simple DIY cure for this; the best course of action if this is suspected is to seek professional assistance to have the key reprogrammed and matched to the vehicle.
If replacing the battery in the key does not solve the problem, try to start the vehicle with the spare key. If this works, the problem obviously involves the other key. However, if the spare key also does not solve the problem, the issue is only resolvable by referring the vehicle to the authorized dealer for professional diagnosis and repair/reprogramming.
WARNING: Do NOT disconnect the battery in an attempt to “reset” the immobilizer unless the manual explicitly states that the battery must be disconnected at this point. Disconnecting the battery can have unpredictable results, which can include causing some control modules (including the immobilizer module) to lose some or all of their programming. If this happens, the only remedy is reprogramming of affected modules, which should NOT be attempted on a DIY basis, and especially not with non-professional grade software and equipment.
This is not so much a step toward resolving the problem as it is a recommendation not to proceed with the diagnostic procedure beyond Step 3. If the problem persists, the better option is to refer, or remove the vehicle to the authorized dealer for professional diagnosis and repair.
Codes Related to P1259
There are no codes directly related to P1259. Any problem such as abnormal input or system voltages, intermittent faults, or high resistances in any part of the immobilizer control circuit will set code P1259.
Below are some examples of definitions of code P1259 that do not relate to the anti-theft system. Note that this list is not definitive, and that code P1259 may have other definitions than those supplied here. Always refer to the manual for the application being worked on to determine the exact definition of P1259 as it applies to that particular application.
- Acura – VTEC System Malfunction
- Chrysler/Dodge/Jeep – Glow Plug Module Control Over Current
- Honda – VTEC System Circuit Fault (Bank 1)
- Volkswagen/Audi – Engine Coolant System Valve Short to Ground
- Volvo – Engine Coolant System Valve Short to Ground
Other Manufacturer Specific Definitions for P1259Engine Coolant System Valve Short To Ground (Volkswagen)
Camshaft position (CMP) actuator - circuit malfunction (Acura)
Engine Coolant System Valve Short To Ground (Audi)
VTEC system malfunction (Honda)
VTEC system - malfunction (Isuzu)