2007 Chevy Suburban P0641 and P1682 Codes: Causes of Reduced Engine Power and Traction Control Issues

Check the official TSBs at http://www.bbbind.com/free-tsb for wiring diagrams specific to your 2007 Chevy Suburban. The ECM relies on two separate ignition 1 voltage circuits: one from the powertrain relay (via fuse 5) and another from the run/crank relay (via fuse 56). If the ECM detects a voltage difference between these circuits, it sets DTC P1682. P0641 relates to the internal 5-volt reference buses in the engine control module. Each bus supplies a stable 5V reference for multiple sensors (such as MAP, FTP, CMP, and APP). A fault on one reference circuit can affect all sensors connected to that bus. The ECM continuously monitors these reference voltages to ensure sensor accuracy.

Here is a diagram showing the 5V reference voltage circuits in the engine control system—useful for understanding how sensor readings are referenced and monitored.

Thanks for the detailed explanation. Based on the wiring diagram, do I need to test only the sensors connected to Voltage A (MAP, FTP, CMP, APP), or should I check all sensors that share the same reference bus? I suspect there's a correlation between them as mentioned by cj1—does a fault in one sensor affect others on the same reference line?

P0641 is triggered when the reference voltages from the ECM’s internal buses don’t match. These reference voltages depend on stable battery power (B+) reaching the ECM. A mismatch may stem from a faulty relay or poor grounding, which can also trigger P1682.

cj1 wrote: Wed Nov 14, 2018 12:31 pm P1682 Description: There are two ignition 1 voltage circuits supplied to the Engine Control Module (ECM). The first comes from the powertrain relay (fuse 5), powering throttle actuator control (TAC) circuits. The second comes from the run/crank relay (fuse 56), powering other internal ECM functions. If the ECM detects a difference in voltage between these two circuits, DTC P1682 is set. P0641 Chevrolet Description: The ECM has two internal 5V reference buses—Reference 1 and Reference 2. Each bus powers multiple sensors. A fault on one reference circuit affects all sensors connected to that bus. The ECM monitors the voltage levels on these reference buses. Note: The symptoms appear intermittent—after clearing the code, the vehicle runs fine for about five minutes before returning to fault status. This suggests an intermittent issue rather than a permanent internal PCM failure. Possible root causes: - Faulty powertrain or run/crank relay - Poor wiring or connection in either circuit - Voltage mismatch due to degraded battery or ground I would prioritize checking the relays and their associated fuses before assuming P0641 is directly caused by a sensor fault—P1682 may be the upstream trigger.

Relay diagrams for both powertrain and run/crank relays: - Run/Crank relay supplies 12V to ECM via fuse #56 (15A) - Powertrain relay supplies 12V to ECM via fuse #5 (15A) The difference in voltage between these two circuits is what triggers P1682. This confirms that a faulty relay or loose connection could be the source of both DTCs.

Thanks for the help. I disconnected the battery and took the vehicle for a drive earlier today. After about 15 minutes, the same warning messages reappeared—Reduced Engine Power, Stabilitrak, and Traction Control. This suggests an intermittent or electrical issue rather than a mechanical one. I’ll continue troubleshooting tonight.

Quick update: I was out of town and delayed my diagnosis. Tonight, after clearing the codes and driving for about 10 miles at various speeds (up to 55 mph), the check engine light came back on with P0641, P1682, and a new code—P0341 (Camshaft Position Sensor A Circuit Range/Performance – Bank 1). This raises concerns: could this be related to relay issues or a more serious electrical fault in the ECM?

A less common but possible cause: inspect the airbag module under the driver’s seat. Water damage can create short circuits without blowing fuses, leading to DTCs like P1682 and others due to ground faults in the ECM or related modules.

Did you ever resolve this issue? I'm experiencing exactly the same symptoms on my 2007 Chevy Suburban. Any advice would be greatly appreciated!