P1684 – Battery has been disconnected within the last 50 starts (Chrysler, Dodge, Jeep, and Plymouth)

By Reinier (Contact Me)
Last Updated 2018-03-01
Automobile Repair Shop Owner

Manufacturer Specific Definitions for P1684

Table of Contents

1. What Does Code P1684 Mean?
2. What are the common causes of code P1684?
3. What are the symptoms of code P1684?
4. How do you troubleshoot code P1684?
5. Codes Related to P1684
6. Get Help with P1684

What Does Code P1684 Mean?

SPECIAL NOTES: Since carmakers are free to assign any problem to any P1XXX trouble code, it sometimes happens that a trouble code, OBD II code P1684 in this instance, can mean vastly different things depending on the problem any given carmaker has assigned to this code. One unfortunate consequence of this is that many generic code readers are sometimes not programmed with all the definitions in use for a particular P1XXX code, and in the case of P1684, there is a lot of confusion about which definition of this code relates to which manufacturer.

While this guide cannot provide detailed information on all the definitions of code P1684 (and the implications of those definitions), for all applications that use this code, it can provide some information on the two predominant definitions of the code, the first being OBD II code P1684 – “Battery has been disconnected within the last 50 starts” used by Chrysler, Dodge, Jeep, and Plymouth, and the other being OBD II code P1684 – “Metering Oil Pump Position Sensor Circuit Malfunction”, which is used by Mazda to indicate issues with lubrication on Wankel (rotary) engines.

Note though that there are still other definitions of code P1684 in current use, and some information on these definitions can be found in the Related Codes section of this guide. However, the information presented here is intended for general informational purposes only, and while every reasonable effort has been made to ensure that all details are correct, the information presented here should NOT be used in any diagnostic procedure(s) without proper reference to the application’s repair manual. END OF SPECIAL NOTES.

Overview of P1684 – “Battery has been disconnected within the last 50 starts”

OBD II fault code P1684 is a manufacturer specific code that is defined by Chrysler, Dodge, Jeep, and Plymouth, as “Battery has been disconnected within the last 50 starts”, and on these applications, code P1684 is set when the PCM (Powertrain Control Module) detects that the battery had been disconnected, or that full battery voltage had been lost during the last 50 start-up cycles.

Be aware though that the definition of code P1684 – “Battery has been disconnected within the last 50 starts” on Chrysler, Dodge, Jeep, and Plymouth applications does NOT mean that the battery has to be physically disconnected for the code to set. What this definition really means is that any problem or circumstance that causes full system (battery) voltage to be lost, or not to be available to any part of the electrical system or control module, can set this code.

Such circumstances could include defects or malfunctions of any component(s) of the charging system, PCM or other control module faults, damage to wiring that interrupts current flow to various control modules, or disconnection/replacement of the battery without having a memory saving device installed.

In many cases, the presence of code P1684 on Chrysler, Dodge, Jeep, or Plymouth applications means nothing more than an indication that either the battery was disconnected within the last 50 starts, or that system power had been lost for some reason during the last 50 starts. Moreover, the code will usually, but not always, be automatically reset, or cleared by the PCM if the code does not occur again within the 50 start-ups following the start-up event during which the code was set.

What are the common causes of code P1684?

Common causes of code P1684 – “Battery has been disconnected within the last 50 starts” could include the following, but note that the causes listed here do not represent a complete list of all possible causes. Refer to the manual for the application being worked on for detailed information on all possible causes of this code for that particular application.

• Disconnecting the battery either with the engine running, or while the ignition was switched on
• Replacing the battery without first installing a memory saving device
• Defects in the charging system that cause under charging of the battery, and hence low system voltages
• Poor connections between battery terminals and battery posts, caused by corrosion or sloppy maintenance practices
• Loss of battery ground due to poor cable connections on either the engine of body, or both
• Failure to program the replacement battery’s technical details/information into the PCM where this is required
• Damage to wiring and/components that results in a loss of communication between two or more control modules that use the CAN bus system for communication of vital control inputs

What are the symptoms of code P1684?

The most common symptom of P1684 on affected applications is the presence of a stored trouble code, and an illuminated warning light. However, the immediate absence of serious symptoms, which could include driveability problems, should NOT be taken as an indication that no damage to the system had occurred, since some symptoms can take a while to manifest.

As stated previously, the battery does not have to physically disconnected for this code to set, but since the affects of losing power to the system can (and often does) produce erratic, unpredictable, and often-confusing symptoms, many mechanics (including professional technicians) often fail to make the connection between the loss of system power, and the sometimes-bewildering array of symptoms and additional fault codes that can come with this code, especially when the battery has not been replaced in the recent past. Moreover, disconnecting a battery terminal to “reset a computer” or to “clear some fault codes” can often induce, or greatly aggravate some symptoms.

Below are details of some symptoms that may, or may not, be present with code P1684, but note that this list is not exhaustive. Refer to the manual for the application being worked for detailed information on all possible symptoms that could affect that particular application-

Loss of KAM (Keep Alive Memory)

The KAM chip in a PCM holds all the values and settings the PCM had “learned” from the moment it was first energized. Typical values include fuel trim settings, transmission shift points, and all other settings that are adaptive. Moreover, the KAM chip also contains all fault codes ever stored, all their accompanying freeze frame data, and the results of all self-tests the PCM had ever run on the emission control system.

All that disconnecting the battery will do in an attempt to clear P1684 is to restore the original base, factory settings for the air/fuel mixture, idle speed, and a few other control functions. Thus, if the problem that set code P1684 is not resolved, the code will be set again, and although it may take a day or two, the code will return, along with all the additional codes and driveability issues that were present originally.

Vehicle will not pass an emissions test

Even if the battery had not been disconnected, the presence of P1684 means that the PCM is almost certainly not able to complete all, or any of the self-tests (readiness monitors) it needs to perform on the emission control system at every start-up.

Bear in mind that the test equipment at testing stations does not measure the emissions of a vehicle; what this equipment does is check that the vehicle’s own diagnostic functions are able to monitor its own emissions. Thus, while P1684 is present and the battery is disconnected to “clear” the code, the test equipment at the testing station will recognize both the attempt at circumvention of the law, and the fact that code P1684 is preventing the execution of self-tests, with the result that the vehicle will fail the emissions test for as long as P1684 is present, and its underlying cause is not resolved.

Transmission may not shift properly

Regardless of the cause of code P1684, the transmission module may have to be reprogrammed as a result of the loss of power. In some cases though, the TCM (Transmission Control Module) will relearn all the settings it had lost, but usually only after the code had been resolved and cleared with a professional grade code reader, or when the code does not set again within 50 starts from the start cycle during which the code was set. Relearning usually takes anywhere from 50, to 100 miles of driving.

BCM (Body Control Module) may be affected

Again, regardless of the cause of P1684, the loss of power to the system can cause the BCM to stop working correctly, and in some cases, to stop working altogether until the module is either reprogrammed, replaced, or allowed to relearn all the settings it had lost. Worse, though, on vehicles with CAN (Controller Area Network) systems, the BCM acts as the “gate keeper” module for the system so when this module fails, all communication between some, or all of the control modules on a vehicle can be interrupted, which means that nothing on the vehicle may work for as long as the underlying cause of code P1684 is not resolved.

Steering angle sensor may not work

Even a momentary loss of power could cause the steering angle sensor on affected vehicles to lose all its learned settings and values, which could affect safety systems like stability control and others, until the sensor had relearned its settings.

Anti-theft system may be disabled

Like with the steering angle sensor, even a momentary loss of power could disable the anti-theft system by causing the system to lose some, or all its learned and programmed settings.

How do you troubleshoot code P1684?

NOTE #1: Note that the loss of system power does not always result in component damage or even noticeable symptoms, but when damage does occur, the required diagnostic/repair procedures are largely make and model specific. When diagnosing code P1684 on Chrysler, Dodge, Jeep, and Plymouth applications, always refer to the manual for the application being worked on for detailed information regarding this code (and its implications) as it relates to the affected application.

NOTE #2: In cases where symptoms do appear, these will almost always be indicated by codes other than P1684, but be aware that while some additional codes may be manufacturer specific, others are likely to be generic. Always refer to the manual for the application being worked on for detailed information on codes, and their likely symptoms, other than P1684.

NOTE #3: Since most manufacturers do not provide information on the possible harmful effects that go with disconnecting a vehicle battery or losing system power for whatever reason, it often happens that even professional mechanics and technicians sometimes make the mistake of disconnecting the negative battery terminal to “reset the computer”. “Resetting a computer” by disconnecting the battery is NOT recommended, unless the manual clearly states that disconnecting the battery is required at some point during the diagnostic process.

Step 1

Record all fault codes present, as well as all available freeze frame data. This information could be of use should an intermittent fault be diagnosed later on.

NOTE: In some cases, the event(s) that set code P1684 on Chrysler, Dodge, Jeep, or Plymouth applications may have damaged the CAN bus (Controller Area Network) system, which is generally not accessible with cheap, generic code readers. Accessing this system is best accomplished with professional grade diagnostic equipment, but even so, interpreting the data requires above average diagnostic skills, as well as expert level knowledge of the application being worked on. If it is suspected that the CAN bus system may have sustained damage, the wiser option is to refer the vehicle for professional diagnosis and repair.

Step 2

If there are other codes present along with P1684, it is likely that these codes are the result of P1684, rather than its cause. Therefore, note the order in which the additional codes were set and stored, and resolve these codes strictly in this order.

If only P1684 is present, consult the manual on the correct procedure to clear the code, especially if the battery had been replaced in the recent past.

NOTE: In some cases, a successful battery replacement requires that all the (technical) information about the battery be programmed into the PCM. This information usually includes the battery’s CCA rating, serial number, and other information the PCM needs to adapt the alternators’ charging rate as the battery ages. Make sure that if this information is required by the PCM, it has been entered correctly to avoid a recurrence of the problem.

Step 3

If the code persists, it is likely that either the underlying cause of the code has not been resolved, or that not enough start cycles (50) have elapsed since the code was set. However, if there are no other codes (active or pending) present, it is almost certain that the code will reset automatically once the required number of start-up cycles have completed successfully. Operate the vehicle normally until the required number of start-up cycles have been reached, and rescan the system to see if the code is still present.

Step 4

If the code returns, and especially if codes other than P1684 return as well, it is likely that an intermittent fault is present in the system. Be aware through that given the large number of possible causes of this code, finding and repairing an intermittent fault may be a near impossible mission for non-professional mechanics, and especially if the CAN bus system is involved.

If it is suspected that an intermittent fault is the cause of code P1684, the wisest option by far is to refer the vehicle to a dealer for professional diagnosis and repair, since even one mistake during the diagnostic process, such as disconnecting the battery while engine is running, or the ignition is switched “ON”, can cause irreparable damage to the vehicles’ entire electrical system.

Codes Related to P1684

NOTE: There are no codes directly related to P1684 – “Battery has been disconnected within the last 50 starts”, but many manufacturers have assigned different definitions to this code. Below are some examples, but take note that as with any manufacturer specific code, the manual for the application being worked should always be consulted for detailed information about the code as it relates to that particular application.

• P1684 – Fiat – “Motorised throttle (plausibility)”

This means that there is a discrepancy between the actual, and the desired or expected position of the throttle. The cause is often related to wiring between the throttle and the PCM.

• P1684 – Buick / Cadillac / Chevrolet / GMC / Oldsmobile / Pontiac / Saturn – “Driver 5 Line 4”

This definition of the code relates to PCM faults, and in particular, defects or malfunctions of drivers in the PCM that control devices like solenoids and relays. Be aware though that there is at least one other definition of code P1684 relating to Chevrolet, P1684 – “Transmission Control Module Power Up Temperature Sensor Performance”.

• P1684 – Honda / Acura – “Throttle Valve Return Spring Performance Problem”

On Honda applications, this code indicates a problem with throttle control due to a sticky, broken, or maladjusted return spring on the throttle.

• P1684 – Mini – “Electronic throttle control monitor level 2/3 – clutch torque min error”

This is not a common code, and hence there is no reliable diagnostic/repair information available for it outside of the dealer network. Consult the manual for the application for detailed information.

• Volkswagen/Audi/Volvo – “Contr. Unit Programming Communication Error”

Note that this code does not exist on vehicles made prior to 2002, but where it does occur on later models, it refers to programming issues within the PCM. Also, note that the VAG equivalent for this code is VAG DTC 18092.

SPECIAL NOTE: this list of alternative definitions of code P1684 may not be complete, or exhaustive. Moreover, the information regarding this code as displayed by generic code readers (and that of many other manufacturer specific codes), should be treated with a great deal of circumspection. For instance, some code readers will display code P1684 as “Metering oil pump position sensor circuit” on some Ford applications, even though Ford products do NOT have oil-metering pumps. Oil metering pumps are only used on Mazda applications that are fitted with Wankel (rotary) engines, about which more can be read in the Mazda area on this site. END OF SPECIAL NOTES.

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