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2011 Chevy Silverado Duramax P0708 Code: Causes, Diagnosis & Fix - Transmission Fluid Level Solution

Model: Silverado Fault Code: P0708 Posted: 2019-10-14 11:42

I own a 2011 Chevrolet Silverado with a Duramax engine and have been consistently encountering the P0708 diagnostic trouble code. I've already replaced the oil-filled harness (between the range sensor and P/N switch), tried both aftermarket and original Allison transmission range sensors, and even swapped out the TCM — none of these fixes resolved the issue. The truck exhibits a strange behavior: it will shift into forward gear, then unexpectedly drop into neutral. When I give it throttle, it briefly returns to forward gear. I've also replaced the park/neutral position switch with no improvement. I'm now wondering what I might be overlooking. The P070 or P0708 code indicates that the transmission range sensor is detecting conflicting gear positions for more than 30 seconds — if this occurs twice in a row, the vehicle enters 'limp-home' mode and the check engine light illuminates. The key insight from another user: when the truck entered limp-home mode, the D-line indicator disappeared and manual shift mode stopped working. A clunk was heard under the vehicle, and it was later discovered that transmission fluid had not been checked after a filter change. After adding Dexron 3 to bring the level up to the low mark, the code cleared and the truck functioned normally. This suggests that low transmission fluid levels may be causing false signals to the TCM, leading to misinterpretation of gear position — which directly triggers P0708. I'm seeking confirmation: could low transmission fluid be a common yet overlooked cause of this code in 2011 Silverado Duramax models? How can I verify proper signal integrity from the range sensor and TCM using a volt/ohm meter and wiring diagrams? Any advice or diagnostic steps to get my truck back on the road would be greatly appreciated.

Related fault codes

P0708

Comments (6)

Anonymous 2019-10-14 13:49

Yes, the harness I replaced was between the transmission range sensor and the P/N switch. To accurately diagnose the issue, it's essential to verify that signals sent from the range sensor are properly reaching the TCM. For detailed wiring diagrams and signal specifications, subscribing to ALLDATA.com or similar technical resources is highly recommended. The Transmission Control Module (TCM) relies on the transmission range sensor — also known as the inhibitor switch — to determine the shift lever position. If the TCM detects conflicting gear signals for more than 30 seconds, it will set code P0708. Repeated occurrences trigger 'limp-home' mode and disable transmission functionality. For more information: https://www.alldata.com/p0708

Anonymous 2019-10-14 14:36

Yes — the issue was in the harness itself, specifically within the case. I also inspected two feet of wiring leading to the TCM and found no physical damage or nicks. This ruled out wire breaks or insulation issues.

Anonymous 2019-10-14 16:05

The most effective next step is to verify transmission signals using a volt/ohm meter and reference the official wiring diagram for your 2011 Silverado Duramax. Confirming signal voltage and continuity will help isolate whether the problem lies in sensor output or TCM input.

Anonymous 2019-10-14 19:03

I'll perform a full signal check tomorrow using a multimeter and the factory wiring diagram to verify transmission range sensor signals to the TCM.

Anonymous 2023-04-01 16:59

Did you ever find a solution? We're experiencing the same P0708 issue on our 2011 Silverado Duramax. Any updates or troubleshooting steps would be very helpful.

Anonymous 2024-07-11 10:13

I recently had the P0708 code appear and the truck entered limp-home mode. I noticed that the D-line indicator disappeared and manual shift mode stopped working. A distinct clunk was heard under the vehicle at the time. While driving home, I recalled that I had replaced the transmission filter previously but hadn't checked fluid levels afterward. The fluid level was significantly below the minimum mark — I had nearly a full quart of Dexron 3, so I drained it and topped it up to the low-level line. After adding another 1–2 quarts as a safety margin, I reset the system. The check engine light turned off, and during a test drive, the transmission shifted normally with no issues. This strongly suggests that low transmission fluid levels can cause false gear position signals, triggering P0708 — even if all sensors and wiring appear intact. This is a critical but often overlooked factor in Duramax Silverado troubleshooting.