P0702

Code

Generic P — Powertrain

Transmission Control System Electrical

Brand: Generic

Type: P — Powertrain

Views: UK: 32 EN: 54 RU: 38

AI status

Completed

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Page language: EN

Causes

Low or intermittent battery voltage / weak battery
Poor or corroded ground(s) at transmission or control module
Blown fuse or faulty relay supplying the transmission control module
Damaged, corroded or disconnected wiring/connector to TCM or sensors
Faulty transmission control module (TCM) or PCM
Intermittent CAN bus or serial data communications

Symptoms

Malfunction Indicator Lamp (MIL) illuminated
Transmission may enter limp/limitation mode
Erratic shifting, harsh or delayed shifts, or failure to shift
Failure to engage gears or stuck in a single gear
Intermittent transmission operation or loss of drive
Possible loss of communication with transmission on scan tool

What to check

Retrieve freeze frame and all stored codes (scan tool) and note events/conditions
Verify battery state-of-charge and charging system voltage (key ON ~12.0–12.8V, engine running ~13.5–14.8V)
Inspect and wiggle-test wiring and connectors at the TCM and transmission for corrosion, bent pins or water
Check fuses and relays related to transmission control power/ignition circuits
Verify good chassis and engine/transmission grounds (clean and ensure tight connections)
Check for lost or intermittent CAN/serial communication messages with a scan tool

Signal parameters

Key ON battery voltage at TCM power terminal: typically ~12V (vehicle-specific)
Engine running charging voltage at TCM: typically ~13.5–14.8V
Ground resistance from TCM ground pin to chassis: ideally
CAN bus idle voltages (vehicle-specific): common-mode ~2.5V; CANH ~2.5–3.5V, CANL ~1.5–2.5V
Transmission shift solenoid coil resistance (typical range for many designs): ~6–30 Ω (check OEM spec)
Quiescent module current draw: small (vehicle-specific); large unexpected draw may indicate internal fault

Diagnostic algorithm

Connect a full-function scan tool. Read and record all transmission and powertrain codes and freeze-frame data. Note if communication to the TCM is lost intermittently.
Verify battery voltage (key ON and engine running). Charge or replace battery if low. Check charging system under load.
Inspect all relevant fuses and relays for transmission control/TCM power and replace if suspect.
Visually inspect TCM and transmission connectors for corrosion, bent pins, water entry, or damage. Securely reseat connectors.
Back-probe the TCM power and ground pins. Confirm proper voltage and good ground while performing wiggle tests on harness to reproduce fault.
Check CAN/serial communication lines with an oscilloscope or scan tool: verify idle voltages and presence of messages. Repair short/open/short-to-ground as required.
Measure resistance and continuity of shift solenoids and related wiring if accessible. Compare to OEM specs and check for shorts to ground or battery.
If wiring and power/ground are OK but fault persists, consider replacing or reprogramming the TCM per OEM procedure. Verify software updates and TSBs before replacement.
After repairs, clear codes and perform road test to confirm fault does not return and transmission operates normally.
Safety note: disconnect battery when performing high-voltage repairs or when instructed by OEM procedures. Follow lockout/tagout and proper ESD precautions for module handling.

Likely causes

Loose, corroded or damaged connector at the TCM
Low battery voltage during key on/engine start
Failed or intermittent TCM
Open or short in power/ground/communication wiring to the TCM
Blown fuse or bad power relay for transmission control
Faulty speed/position sensor causing erroneous TCM behavior

Fault status

⚠️ Status

P0702 — Transmission Control System Electrical: The control module detected an electrical fault or communication error in the transmission control system. Inspect power, ground, wiring/connectors, fuses/relays, CAN/communication and the TCM. Repair or replace affected components and confirm with a scan tool.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 1-3 hours