Code
P1704
FIAT
P — Powertrain
Autotransmission | Secondary pressure sensor
AI status
Completed
Completed
100%
Causes
- Faulty secondary pressure sensor (internal failure)
- Damaged, corroded or disconnected sensor connector or wiring harness
- Short to ground or to battery in signal/reference circuit
- Low or contaminated transmission fluid affecting pressure readings
- Valve body or hydraulic control block fault (sticking valve, leak)
- Failed TCM/ECU or poor ground at control module
Symptoms
- Transmission may go into limp/reduced‑gear mode
- Harsh, delayed or incorrect shifting
- Transmission warning light or MIL illuminated
- Stored transmission-related trouble codes
- Possible slipping or unexpected gear engagement behavior
What to check
- Read and record freeze frame data and live sensor values with a capable scan tool
- Visual inspection of sensor, connector and wiring for damage, corrosion, pulling or pin pushout
- Check transmission fluid level and condition (contamination, metal debris)
- Backprobe sensor signal, reference and ground pins while monitoring voltage
- Wiggle test harness while observing live data and watch for intermittent changes
- Check TCM power and ground circuits and related fuses/relays
Signal parameters
- Sensor type: analog pressure sensor (typically 3‑wire: 5 V reference, signal, ground)
- Reference: approx. 5 V supply from TCM (verify with meter)
- Signal voltage: commonly in the range ~0.5–4.5 V proportional to pressure (consult OEM spec for exact values)
- Expected behavior: signal changes with engine speed/gear and when hydraulic pressure changes
- Resistance: varies by design—consult OEM service data for exact ohms if measuring with meter
Diagnostic algorithm
- Connect scan tool, read codes and freeze frame; note when code set and any concurrent codes.
- Perform visual inspection of sensor, connector and wiring; repair obvious damage and clear code to retest.
- With ignition on, backprobe sensor connector: verify 5 V reference present, good ground and that signal toggles with engine/transmission operation. Record voltages.
- Wiggle harness and connectors while watching live data for intermittent faults; repair/replace connectors or wiring as needed.
- Check transmission fluid level and condition; top up or service fluid if low/contaminated and retest.
- If electrical checks fail (open/short), trace and repair wiring or replace connector. If wiring is good but signal out of range, replace the secondary pressure sensor.
- If replacement sensor and wiring are good but fault persists, inspect valve body/hydraulic circuits for internal leaks or sticking valves; measure line pressure with a calibrated mechanical gauge and compare to OEM values.
- If hydraulic pressures are correct and wiring/sensor are verified, evaluate TCM for internal fault and consider reflashing/updating software or replacement as final step.
- After repairs, clear codes and perform road test and full scan tool verification to confirm repair.
Likely causes
- Open/short or poor connection at sensor connector
- Failed pressure sensor
- Contaminated/low transmission fluid or internal hydraulic leak
Fault status
Status
Transmission control module detected invalid/absent secondary pressure sensor signal (circuit malfunction/out of range). Fault stored and MIL may be illuminated; limp mode possible.
Repair difficulty: Medium
Diagnostic time: 1-3 hours
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