P0978

P0978 is the Shift Solenoid B Control Circuit Intermittent — the TCM sees SS-B circuit voltage drop out of normal operating range, then return, without staying in a stable short or open. Intermittents on shift solenoids cause non-reproducible harsh shifts, brief flares, or single-event limp-mode trips that clear before the customer can show you. Cheapest-first: freeze-frame data is your best friend here — pull the snapshot, note the fluid temp, vehicle speed, and gear range when the code set, and replicate those conditions on a road test with a scan tool live-recording SS-B commanded state and circuit voltage. Then wiggle-test the case connector and the harness route between TCM and trans with the engine running and a scan tool live on SS-B; movement that toggles the PID points at the connector or chafe point. Ohm SS-B pin-to-pin at the case both cold and at full operating temp — a winding that ohms 14 ohms cold and 4 ohms hot is breaking down thermally even though it passes a static check (spec should stay within 8-30 ohms across temp range; 19-31 ohms GM 4L60E, 9-16 ohms Ford 4R75W, 11-15 ohms Chrysler 545RFE pack, 10-15 ohms Toyota A340/A750). Ohms-to-ground should be >100k ohms on each pin both cold and hot — a reading that drops under load means partial short. Active current should track 0.5-1.5 A at full command; current excursions or dropouts during a road-test recording confirm the intermittent. Expensive-misdiagnosis caveat: on Chrysler 545RFE/68RFE intermittent P0978 is the textbook early-warning sign of pack thermal degradation — pack passes cold, faults hot, customer comes back. Single-circuit repair is not a supported procedure on this trans; full solenoid-pack replacement is the right answer once case connector and external harness are confirmed clean, and chasing connector cleanings or single-wire splices on a 545RFE/68RFE pack-failure case loses the customer's trust along with the come-back labor.

Vehicle-specific patterns: 1996-2007 GM 4L60E sets intermittent P0978 from a marginal case connector that loses pin-fit during temperature cycling — connector body replacement is the documented fix, not contact cleaner. 2003-2010 Dodge Ram 1500/2500 with the 545RFE and 2007-up 68RFE sees P0978 as the documented precursor to outright pack failure, and aggregated AAMCO/RepairPal cost data places solenoid-pack replacement at $500-900 parts plus labor at independents in the 70k-150k mile window. 2007-2013 Ram HD with the Aisin AS69RC throws intermittent P0978 from valve-body sleeve wear scoring the SS-B plunger after a torque-converter shudder event — valve-body R&R, $800-1,400. 2001-2010 GM HD with the Allison 1000 (LCT1000) sets intermittent P0978 from PCS-2/PCS-3 wire chafe at the case-flange ridge under thermal expansion — Allison Transmission service guidance addresses this with a harness re-route procedure before solenoid or pack replacement. Estimated repair: $300 to $1,500.