P0703 and P0706: brake switch B and transmission range sensor

An automatic gearbox needs two pieces of information before it will do anything: which range the driver selected, and whether the brake is being pressed. These two codes cover the failure of each.

Code	Meaning
P0703	Brake switch B circuit malfunction
P0706	Transmission range sensor circuit range/performance

Related: P0705 transmission range sensor.

P0706: the selector position

The range sensor — also called the neutral safety switch or inhibitor switch — tells the transmission control module which position the lever is in.

Range/performance means the signal is present but implausible: two positions reported at once, a transition that skipped a position, or a value that does not correspond to any valid range.

Symptoms

• No crank in Park, but it starts in Neutral. The single most diagnostic symptom, and it means the switch is not reporting Park correctly.
• The wrong gear indicated on the dashboard, or none at all.
• Harsh shifts, because the module is calibrating for the wrong range.
• No reverse lights, since they are commonly switched by the same sensor.
• Limp mode, with the gearbox holding one gear.

That last one is why this is not a cosmetic fault: limp mode, what it is and how to exit.

Causes

Adjustment. External switches on the gearbox are adjustable, and they drift. A switch out of alignment reports the wrong position or two positions during the transition. Check adjustment before replacing anything — it is often the whole fix.

Contamination. External switches take road spray and salt. Internal ones sit in transmission fluid, and degraded fluid attacks the contacts.

Selector cable stretch. The lever says Drive, the switch sees something between Drive and Neutral. Common on higher-mileage vehicles and frequently misdiagnosed as an internal fault.

Wiring, at the gearbox connector.

P0703: the brake switch, transmission side

Many vehicles run two brake switch circuits: one for the engine and cruise control, one for the transmission and the shift interlock.

P0703 covers the second. Symptoms:

• The selector will not move out of Park, because the interlock never releases.
• The torque converter clutch behaving oddly, since it must release when braking: P0740 and P0741 torque converter clutch.
• Cruise control faults, where the same switch feeds both.

The causes are the same as the other brake switch circuit, including the small rubber pedal pad that falls out and leaves the plunger extended: P0571 brake switch circuit.

Read the two together

The combination narrows the diagnosis considerably.

Codes	Likely cause
P0706 alone	Range switch adjustment or the switch itself
P0703 alone	Brake switch or its adjustment
Both	Shared wiring, ground, or a supply feeding both
Either plus P0700	Read the transmission module for the real detail

That last row matters. P0700 is a pointer code — it means the transmission module has something to say, and the specific code lives in that module rather than in the generic list.

What to check in the data

Selected gear and actual gear, side by side.

Observation	Meaning
Both agree through every position	Range sensor healthy
Selected value jumps or shows an invalid position	Sensor or adjustment
Selected lags the lever by a position	Cable stretch or misadjustment
Brake status does not change with the pedal	Brake switch

Move the lever slowly through every position with the engine off and ignition on, watching the reported value. A position that flickers or skips is the fault, shown directly.

Do not start with the gearbox

The expensive misdiagnosis here is treating harsh shifting and limp mode as an internal transmission problem when the module simply does not know which range is selected.

A switch, a cable adjustment or a connector is a fraction of the cost of a gearbox. Establish that the module has correct inputs before anyone opens anything.

Transmission not shifting diagnosis and how to read a workshop quote.

Where to start

1. Try starting in Neutral — if it works, the range switch is the fault.
2. Watch selected gear in live data through a slow sweep of the lever.
3. Check the reverse lights as a free cross-check.
4. Check switch adjustment before replacing it.
5. Check the selector cable for stretch.
6. Read the transmission module for the codes behind P0700.

Try it on the free tier of the app — pair an ELM327 adapter and watch the reported gear position while moving the lever through every range. A position that never appears is the whole diagnosis.