1991 GMC Sierra "obd 2 code reader 91" Questions

...2 second. This is sometimes called the Normal or System Clear signal. After the diagnosis check, turn the ignition OFF and remove the jumper wire. Compare the codes found to the applicable diagnostic ...

...OBD I vehicles. If the engine isn't running correctly this could cause the transmission not wanting to shift. 2 vehicles that come to mind where I've seen this happen. One was a Pontiac and it ...