P1682 – Driver 5 Line 2 (GM)

By Reinier (Contact Me)
Last Updated 2020-12-21
Automobile Repair Shop Owner

Manufacturer Specific Definitions for P1682

What Does Code P1682 Mean?

OBD II fault code P1682 is a manufacturer-specific trouble code that is defined by carmaker General Motors as “Driver 5 Line 2” and is set when the PCM (Powertrain Control Module) detects a difference in voltage that exceeds a maximum allowable threshold between two circuits that supplies it with battery voltage.

NOTE: While most sources, including official GM sources, list code P1682 with the definition “Driver 5 Line 2”, many online non-official GM sources list this code as P1682 – “Ignition 1 Switch Circuit 2”. In practice, the latter definition describes the same problem as the former. Thus, from a diagnostic perspective, the two definitions are interchangeable.

Unlike almost all other manufacturers that use a single circuit to supply power to the PCM, General Motors products use two circuits to supply the PCM with battery power. One circuit passes through the ignition switch and a relay to the PCM to supply current to all internal circuits associated with the TAC (Throttle Actuator Control) system. The second circuit passes through the run/crank relay and a fuse to supply current to all other circuits in the PCM.

In GM-speak, these two circuits are known as Circuit 1 and Circuit 2, respectively, and in a fully functional system, the current in the two circuits will be equal at all times. However, GM vehicles made between about 2004 and 2015 were known to be fitted with poorly designed ignition switches, and as a result, ignition switch failures were common on vehicles that included many Buick, Cadillac, Chevrolet, GMC, Hummer, Isuzu, Oldsmobile, Pontiac, and Saturn models.

The practical effect of ignition switch failures on these vehicles was that the difference in voltage between circuits 1 & 2 sometimes exceeded 3 volts for longer than 2 consecutive seconds, which caused code P1682 to set. However, an additional complication was that different circuits were affected at different times on different vehicles, and under different conditions, which sometimes produced a bewildering array of symptoms.

For instance, when circuit 1 failed, the throttle actuator was sometimes disabled, and a no-start condition would result. Similarly, when circuit 2 was affected, the fuel pump was sometimes deprived of power, which also resulted in a no-start condition, although the engine would typically crank normally in both cases, although there are exceptions to this.

While a major recall campaign in 2014/15 appeared to have resolved the problem on most GM products, this code still makes random appearances on post-2015 GM products, with much the same causes and symptoms as on pre-2015 models.

Where is the P1682 sensor located?

This image shows a comparison between the poorly designed part (at the top) in GM ignition switches and the redesigned part (at the bottom) that largely corrected the overall design problem.

What are the common causes of code P1682?

Causes of code P1682 are similar on all GM products and could include one or more of the following-

• Failed, failing, or defective ignition switch (Most common)
• Defective fuses or fuse box. Note that under some conditions, such as when the vehicle had been parked in the sun, the fuse boxes on some models would deform, which often caused wiring connections in the fuse box to break or lose contact. This particular issue is known to affect Chevy Trailblazer, GMC Envoy, and Chevy SSR models
• Failed, defective, or malfunctioning PCM relays. Note that in cases where an ignition switch failure affected circuit 1, the reduced power feed to this relay often caused contacts in the relay to arc and burn
• Failed, defective, or malfunctioning fuel pumps, as the result of ignition switch failures affecting circuit 2
• Failed or failing PCM, but note that this code often mimics the effects of a failed PCM or corrupted software. Therefore, the fault must be sought elsewhere before any control module, including the PCM, is condemned

What are the symptoms of code P1682?

Common symptoms of code P1682 are also similar across all affected GM products and could include one or more of the following-

• Stored trouble code and illuminated warning light
• A no-start condition, although the engine would typically crank normally
• In some cases, additional codes may be present along with P1682, depending on whether (or not) the persistent primary problem had caused secondary damage to parts and components