Vehicle Enters Reduced Power Mode with OBD2 Code P2135 - Throttle Body Replacement Not Resolving Issue
I'm experiencing repeated instances of my vehicle entering Reduced Power Mode while driving on the freeway. This issue first appeared two weeks ago, and I took it to a mechanic who diagnosed a faulty throttle body and recommended replacement. After replacing the throttle body, the problem persists. I've returned to the same shop eight times since then, and each time the vehicle enters Reduced Power Mode, OBD2 code P2135 appears. The technician has repeatedly performed relearn procedures using a scan tool, but these have not resolved the issue. I'm increasingly concerned that the root cause may not be the throttle body itself. I've read several forum posts suggesting that P2135 is often linked to electrical issues—such as wiring faults, poor ground connections, or intermittent signal problems in the throttle body circuit—rather than a defective part. The vehicle typically enters Reduced Power Mode after sitting for several hours, though it has only occurred once during active driving so far. Given that I've been back eight times with no resolution, I'm seeking advice on what else should be investigated. Is there a known diagnostic procedure or specific test (like checking TPS data or ground integrity) that could help identify the real cause? I understand that some shops may simply replace parts without thorough diagnostics. I'd like to know if there are any standard electrical checks—such as wiggling connectors while monitoring signal data—that should be performed before concluding it's a defective throttle body.
Do you also have code P0120? Consider taking the vehicle to a mechanic with certified ASE credentials in diagnostics, electrical systems, or driveability. This issue is easily diagnosed using a digital multimeter (DMM), a high-quality scan tool capable of reading live data PIDs, and a solid understanding of how the throttle system operates. GM has historically had wiring and grounding problems related to the throttle body connector. A proper diagnosis would involve checking electrical continuity by wiggling the connector while monitoring signals at the throttle body. Additionally, use a scan tool to monitor TPS1 and TPS2 data—compare their values while gently vibrating the connector. The issue is likely either a wiring fault or an intermittent ground. GM issued a technical service bulletin (PI) addressing this specific problem.