| Neutral Safety Switch/Transmission Range Sensor |
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The neutral safety switch is used to prevent starter operation in all gears other than
Park and Neutral.Voltage should be present when the ignition switch is turned to the
start position. Any other gear the starter circuit is open and voltage is prevented from
turning the starter motor.
The neutral safety switch often has the backup lamp incorporated in its design. If there
is a no start condition this switch can be tested using a voltage meter. A technician
would back probe the “voltage out” wire while someone turns the ignition. Check to see
if battery voltage is coming out of the wires leading to the rest of the starter circuit in the
Park and Neutral positions. If there is voltage coming in to this switch and no voltage
coming out replace the neutral safety switch.
The Transmission Range Sensor is part of the transmission computer control system
found on late model vehicles. It can be analog or digital. Both of these are best
diagnosed with a scan tool. If one is unavailable the analog type can be diagnosed with
an ohmmeter.
The analog type TR sensor is constructed of a series of resisters that reduce the
voltage returned to the PCM according to the desired shift lever position. A technician
would measure the resistance between the appropriate connections and compare
these with manufacturer specifications.
Both the older neutral safety switch and the newer transmission range sensor will
cause a no start condition as well as no back up lamp operation. The TR sensor can
affect several different systems. A misadjusted TR sensor can cause harsh shifting or
confuse the PCM if the resistance is out of specifications.
Park and Neutral.Voltage should be present when the ignition switch is turned to the
start position. Any other gear the starter circuit is open and voltage is prevented from
turning the starter motor.
The neutral safety switch often has the backup lamp incorporated in its design. If there
is a no start condition this switch can be tested using a voltage meter. A technician
would back probe the “voltage out” wire while someone turns the ignition. Check to see
if battery voltage is coming out of the wires leading to the rest of the starter circuit in the
Park and Neutral positions. If there is voltage coming in to this switch and no voltage
coming out replace the neutral safety switch.
The Transmission Range Sensor is part of the transmission computer control system
found on late model vehicles. It can be analog or digital. Both of these are best
diagnosed with a scan tool. If one is unavailable the analog type can be diagnosed with
an ohmmeter.
The analog type TR sensor is constructed of a series of resisters that reduce the
voltage returned to the PCM according to the desired shift lever position. A technician
would measure the resistance between the appropriate connections and compare
these with manufacturer specifications.
Both the older neutral safety switch and the newer transmission range sensor will
cause a no start condition as well as no back up lamp operation. The TR sensor can
affect several different systems. A misadjusted TR sensor can cause harsh shifting or
confuse the PCM if the resistance is out of specifications.