P0973: How to Diagnose & Fix — Shift Solenoid 'A' Control Circuit Low
2 vehicles · 1 makes · $300-$2,500 repair
How to diagnose and fix P0973: most-reported vehicles
Ranked by owner reports. Each card gives the symptoms, how to confirm the cause, the fix, parts and sources for that vehicle.
Chevrolet Silverado 1500 · 2007–2019
P0700 is not a specific fault by itself — it is an umbrella/MIL-request code the ECM stores whenever the transmission control module (TCM) detects an internal transmission problem and asks the ECM to turn on the check-engine light. On the Silverado 1500 it almost always appears alongside more specific companion codes, and the underlying failure follows two dominant, well-documented patterns depending on the transmission. On trucks with the 6L80 six-speed automatic (many 5.3L and 6.2L V8 trucks, plus 2014-onward 4.3L V6 trucks; 2015-onward 6.2L trucks use the 8L90 eight-speed instead), the internal TEHCM (Transmission Electro-Hydraulic Control Module — GM's combined valve body, solenoids, pressure switches, and TCM in a single pan-mounted unit) develops internal circuit-board/solenoid faults from heat and fluid degradation, throwing P0700 together with codes like P0796, P0777, P0842, or P0973 and dropping the truck into limp mode. On older/base trucks with the 4L60E four-speed (2007-2013 4.3L/4.8L), the same P0700 is typically triggered by a failed shift solenoid (P0753/P0758) or a faulty internal mode switch. Because P0700 is a stored 'passenger' code, a scan tool that can talk to the TCM (not just a basic reader) is required to pull the specific sub-code that identifies the actual failed component.
Common Symptoms
- Check engine light on with P0700 stored
- Transmission stuck in limp mode / limited to one gear (often 3rd or 5th)
- Harsh or delayed shifts
- Transmission fails to shift or slips
- Torque converter clutch not locking up / shudder
- No movement or won't shift out of park in severe cases
How to Fix
Do NOT replace parts off the P0700 alone. Use a bidirectional/TCM-capable scan tool to read the companion codes stored in the transmission controller and verify transmission fluid level and condition first (low or burnt DEXRON-VI fluid alone can trigger the chain). For 6L80 trucks, a failed internal TEHCM is confirmed by multiple simultaneous solenoid/pressure codes; the fix is to drop the pan and replace the TEHCM, which MUST then be programmed to the vehicle's VIN with GM calibration files before the truck will start or shift correctly (ordering the OEM unit by the last 8 VIN digits can yield a plug-and-play unit needing no fast-adapt relearn). For 4L60E trucks, replace the specific failed shift solenoid or internal mode switch identified by the sub-code. Repair the wiring/connectors to the TCM if corrosion is found.
Sources for this issue (4)
Chevrolet Silverado 2500HD · 2001–2019
Separate from the well-known torque converter shudder, the Allison 1000 in these trucks is documented for shift solenoid faults that drop the transmission into limp mode. The TCM sets P0700 - a generic 'transmission fault' pointer - accompanied by a specific code such as P0871 or P0872 (pressure switch E reading wrong for the commanded state of shift solenoid E, often caused by the solenoid or a sticking valve). When that code sets, the transmission falls to hydraulic default, the TCM inhibits torque converter clutch engagement, and the truck is left in a single gear, usually third, sometimes refusing to move at all until it is restarted. On a loaded 2500HD this strands the truck. Forum diagnosis repeatedly finds the cause outside the solenoid itself: low or burnt fluid, a loose battery ground, or a chafed harness behind the transmission.
Common Symptoms
- Transmission stuck in one gear (limp mode)
- Check engine light with P0700
- Harsh or no shifts
- Torque converter clutch will not lock up
- Truck will not move until restarted
- Service transmission message
How to Fix
Do not open the transmission on a P0700 alone - read the sub-code first. Check fluid level and condition, then inspect the internal wiring harness pass-through connector, the transmission harness where it routes behind the case, and the battery/chassis grounds, all documented causes of these codes. If the solenoid body is genuinely at fault, the internal control solenoid body and the internal harness are replaced with the pan down. Fluid and filter service on the Allison's real interval (much shorter for tow and plow duty) is the strongest prevention. No recall covers this.
Sources for this issue (5)
- Allison 1000 issues and limp mode - Chevy and GMC Duramax Diesel Forumforum
- Allison 5sp: Limp mode bad solenoid - DuramaxDiesels.comforum
- Allison Transmission P0700 Code Help - Chevy and GMC Duramax Diesel Forumforum
- Allison pressure switch codes - Transmission Digestarticle
- Allison 5sp: Codes set P0847 & P0872 - DuramaxDiesels.comforum
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P0973 code reference
General diagnostic-code context. The code alone does not confirm a cause for your vehicle; use the applicable issue card and its sources.
Frequently asked questions
What does P0973 mean?
P0973 stands for "Shift Solenoid 'A' Control Circuit Low." The shift solenoid 'A' control circuit voltage is below the expected range (too low / shorted to ground).
What are the most common causes of P0973?
The most common causes of P0973 are: Solenoid circuit shorted to ground, Faulty shift solenoid A, Corroded/damaged connector, Internal TCM fault. The specific cause varies by vehicle.
How much does it cost to fix P0973?
Repair costs for P0973 range from $300 to $2,500, depending on the vehicle and root cause.
Which vehicles are affected by P0973?
Au7o has documented P0973 across 2 vehicle models from 1 manufacturers: Chevrolet.
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Content compiled with AI assistance using NHTSA complaints, TSBs, and owner reports. May contain errors. Always verify with your vehicle's service manual.