Network, generic

U0688 Lost Communication With Throttle Position Sensor/Switch G

Check engine lightOn

EmissionsRelevant

Drive cycleNot required

Limp modePossible

Throttle sensor G is the second track of a second throttle body. GM's 23OBDG07 and 24OBDG07 tables, for a program with one throttle per bank, use it for throttle position sensor 2 on bank 2. Both tracks of that throttle travel in one SENT stream, so GM sets U0688 together with U0608 (sensor 1, bank 2) when the line carries no signal, pulse widths fall outside their window or the calibration pulse is off, within 0.13 s and MIL in one trip. NXP's KMA215 shows why: its dual throttle format packs the angle and its inverted copy into a single frame. Raw value checks of track G are P212C under 0.195 V and P212D over 4.805 V, P212B checks synchronisation. Bank 2's throttle can then no longer be positioned reliably, so power is reduced.

Likely causes

SENT, supply or ground wire to the bank 2 throttle body faulty

Throttle body connector loose, wet or corroded

Sensor electronics in the throttle body failed (replaced as a unit)

Engine controller SENT input fault

Symptoms

Check engine light on the first trip
Reduced power, uneven running between banks
U0608 stored at the same time

Repair estimate

DifficultyMediumDIY possible

Parts and labour€60–700

Time0.5–2 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

throttle position sensor gvehicle bus wiring

References: gsi.ext.gm.com, gsi.ext.gm.com, nxp.com, law.cornell.edu.