Damaged or corroded wiring in the STB line between the TCS control unit and the throttle body.; Loose, dirty, or corroded electrical connectors at the TCS module or throttle body.; Failed throttle body assembly with an internal fault on the STB circuit.; Faulty TCS control unit not sending or receiving the proper STB signal.; Poor ground connection for the TCS or throttle body circuits causing voltage irregularities.; Aftermarket electrical accessories improperly tapped into the STB line, introducing interference.

DTC codes / Honda codes / P1690

P1690 · HondaTraction Control System STB Line Failure

Q: What does code P1690 mean?

Traction Control System STB Line Failure. P1690 on Honda vehicles indicates that the traction control system (TCS) has detected a failure on the STB (Steering Throttle Body) communication line, which is a dedicated serial data circuit between the TCS control unit and the throttle body assembly. The computer sets this code when the expected voltage or signal pattern on that line does not match what the TCS module is commanding, often due to an open, short, or excessive resistance in the wiring or a faulty component on that line.

P1690 on Honda vehicles indicates that the traction control system (TCS) has detected a failure on the STB (Steering Throttle Body) communication line, which is a dedicated serial data circuit between the TCS control unit and the throttle body assembly. The computer sets this code when the expected voltage or signal pattern on that line does not match what the TCS module is commanding, often due to an open, short, or excessive resistance in the wiring or a faulty component on that line.

SystemPowertrain

Code typeHonda specific

SeverityMedium

Fix difficultyIntermediate

AreaComputer and output circuits

Symptoms you may notice

The traction control system (TCS) warning light illuminates steadily on the dashboard.
The vehicle may enter limp mode, limiting engine power or disabling traction control entirely.
The throttle may feel unresponsive or sluggish, especially during acceleration from a stop.
In some cases, the check engine light may also come on if the fault affects shared data lines.
Often no symptoms besides the warning light, with the vehicle driving normally in dry conditions.

Common causes, most likely first

Damaged or corroded wiring in the STB line between the TCS control unit and the throttle body.
Loose, dirty, or corroded electrical connectors at the TCS module or throttle body.
Failed throttle body assembly with an internal fault on the STB circuit.
Faulty TCS control unit not sending or receiving the proper STB signal.
Poor ground connection for the TCS or throttle body circuits causing voltage irregularities.
Aftermarket electrical accessories improperly tapped into the STB line, introducing interference.

How to diagnose and fix it

Scan all modules for stored codes and record freeze-frame data to confirm P1690 is active and not historical.
Visually inspect the STB wiring harness and connectors for chafing, corrosion, or loose pins, especially near the throttle body and TCS module.
Measure resistance and continuity on the STB line from the TCS control unit to the throttle body, comparing to factory specifications.
Check for short circuits to ground or power on the STB line with a multimeter while wiggling the harness.
Perform a voltage drop test on the ground circuits for the TCS module and throttle body to rule out bad grounds.
If wiring and grounds are good, substitute a known-good throttle body and retest to see if the code clears.
If the code persists after throttle body substitution, test or replace the TCS control unit as the last step.

STB Line Faults Often Misdiagnosed

A common mistake is replacing the throttle body immediately, but the STB line fault is frequently caused by a chafed wire near the intake manifold where heat and vibration damage the insulation.
The STB line is a low-current serial data circuit, so a standard test light can damage the TCS module; always use a high-impedance multimeter or oscilloscope for testing.
This code can be set by a weak battery or charging system issue that causes voltage spikes, so check battery health and alternator output before condemning expensive components.
Aftermarket alarm or remote start installations often tap into the STB line for tachometer signals, creating intermittent faults that only appear under certain conditions.
On some Honda models, the STB line shares a connector with the cruise control circuit, so a fault in the cruise control switch can set P1690 without any traction control symptoms.

Can I keep driving with P1690?

You can usually drive the vehicle with P1690 set, but traction control and possibly stability assist will be disabled, so avoid aggressive acceleration or slippery conditions. If the engine enters limp mode or the throttle response becomes erratic, have the vehicle towed to a repair shop rather than continuing to drive.

Tools that help

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Guidance is general and written for Honda vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.