P1735

P1735 is a Ford-specific code meaning the First Gear Switch circuit has failed — on the 5R55E/5R55W/5R55S and certain 4R70W variants, the trans uses a dedicated 1st-gear position switch (separate from the MLPS) that confirms the gearbox is mechanically engaged in 1st when the PCM commands 1st gear, primarily for the lockup/coastdown logic and the manual-1 enforcement. Circuit failure can be open, shorted to ground, or shorted to power. Cheapest-first ladder: (1) Pull the harness connector at the trans-case bulkhead and inspect for ATF migration, corrosion, and backed-out pins — same failure path as every other internal-harness Ford trans code ($0, 10 min). (2) Verify the 1st-gear switch signal with KOEO and the scan tool: the switch should pull low (<0.5V) or high (>10V) depending on application when the manual valve is in the M1 detent, and the opposite state in all other positions. (3) Resistance-check the switch contacts from the case-external connector — open circuit in M1 confirms the switch or its internal harness is open; if the switch tests good in M1 but the code persists, the fault is between the case connector and the PCM. (4) Inspect for any recent valve-body work — the 1st-gear switch is often disturbed during valve-body service and can be reinstalled with a pinched O-ring or mis-clocked, causing intermittent contact. Expensive-misdiagnosis caveat: P1735 on a 5R55-series gearbox after a valve-body service is almost always installation-related, not a failed switch — don't order a new switch until you've pulled the pan, inspected the valve-body-to-case interface, and confirmed the switch terminal isn't grounded by a misrouted internal harness.

Vehicle-specific patterns: 1996-2003 Ford Explorer/Mountaineer with the 5R55E and 1997-2011 Ford Ranger with the 5R55E throws P1735 from internal harness contamination and from the 1st-gear switch contact wearing flat after high-mileage manual-1 use (off-road and trailering). 1996-2010 F150 and 1996-2014 E150/E250/E350 vans with the AODE/4R70W (early variants with the discrete 1st-gear switch) see P1735 from the same internal-harness ATF migration path that drives P1701/P1702/P1716. 1996-2010 Mustang with the AODE/4R70W sees P1735 less often because the M1 manual range gets little use. 1996-2011 Crown Vic Police Interceptor sees P1735 in service from heavy stop-and-go fleet cycling. Estimated repair: $50 to $1,200.