← Back to list

2005 GMC Sierra 1500 5.3L Engine P2101 and P2135 Fault: Reduced Power Mode Intermittent Failure Diagnosis

Model: 2005 GMC Sierra 1500 Fault Code: P2101 Posted: 2020-07-23 06:37

I'm experiencing intermittent reduced engine power mode on my 2005 GMC Sierra 1500 with a 5.3L V8 engine, triggered by fault codes P2101 and P2135. The issue occurs intermittently and has persisted despite replacing the throttle body. Initial diagnostics suggested a connection problem, but I'm skeptical—many users report similar symptoms after installing aftermarket throttle bodies. After multiple attempts to resolve it, the issue returned even after driving around the block. The current theory is that rusted frame grounds are causing electrical interference or harness damage, leading to intermittent signal loss between the TAC module and throttle body. A recent repair involved replacing the wiring harness between the TAC module and throttle body, which has temporarily resolved the problem. However, the issue reoccurred during a drive home, triggering P2135 and P2101 again, along with limp mode activation. I'm now considering a full ground inspection due to known rust issues in this vehicle model. A lab scope and real-world test under driving conditions would be ideal for definitive diagnosis. This case highlights the importance of proper wiring integrity and grounding in older trucks with high rust exposure.

Related fault codes
P2101P2135
Comments (10)
Anonymous 2020-07-24 09:36

The scanner initially indicated a connection issue, but I'm not fully convinced. Many users report throttle position sensor (TPS) problems after installing aftermarket throttle bodies—this could be the root cause. If the replacement doesn't resolve it, further investigation into wiring and grounding is warranted.

Anonymous 2020-07-24 10:39

OBD-II scanners are limited in diagnosing intermittent faults like this. A lab scope with real-time signal monitoring and repeatable driving conditions would provide more accurate results. In practice, these issues often require physical inspection and part replacement—time is money, especially when dealing with complex electrical systems.

Anonymous 2020-07-31 17:31

After replacing the throttle body, I drove around the block and immediately experienced a return of reduced engine power mode. I knew it would happen sooner or later—but not this quickly. The current diagnosis points to corroded grounds due to rust on the frame, which may be damaging the wiring harness.

Anonymous 2020-07-31 17:51

A faulty TAC (Throttle Actuator Control) module is a plausible next step—especially given that P2101 and P2135 are related to throttle position and signal integrity. This should be considered before moving on to other components.

Anonymous 2020-09-01 09:32

The issue was resolved after replacing the wiring harness between the TAC module and throttle body. So far, no recurrence has been observed—this appears to have fixed the intermittent power loss problem.

Anonymous 2020-09-01 11:05

Great to hear! A visual inspection of connectors and wiring would have revealed damaged or corroded sections. A wiggle test while the engine is running can also detect loose connections. Thanks for sharing your resolution—it's helpful for others facing similar issues.

Anonymous 2020-09-02 04:08

I'm not fully convinced yet—on my way home, the issue returned and triggered P2135, P1516, and again P2101 during limp mode. The mechanic suspects frame rust is causing electrical shorts in the harness. I plan to inspect all ground connections myself now that our local auto shop has reopened.

Anonymous 2020-09-02 07:12

Did you see any visible damage to the wiring harness? Such as charring or melting?

Anonymous 2020-09-02 07:24

I haven't had a chance to inspect it yet, but when they replaced the harness, they reported it was shorted—likely due to internal corrosion from rust exposure.

Anonymous 2026-01-29 08:24

This issue has been ongoing for years—I'm now experiencing the same symptoms. Was there a definitive fix or long-term solution identified for this specific P2101/P2135 problem on the 2005 GMC Sierra 1500?