P1635 code and how it affects your GM engines
A GM P1635 code means 5 volt reference 1 circuit malfunction. If you remember, most GM engine computer (ecm) sends a 5 volt reference to all sensors when monitoring the engine electronic system. Example is the 5 volt reference 3rd wire you will find on the tps sensor and map sensor along with the ground and signal wires. If this 5 volt reference change in value other than 5 volts, a P1635 will be flagged by the ecm. Some of the symptoms when this code appears are erratic idle speed or occasional engine going into high idle without stepping on the gas pedal.
The most common way to check this GM P1635 code is to measure and verify the 5 volt reference wire at your tps, coolant sensor, egr valve and if possible disconnect each of them one at a time. Hooking it up to a DVOM, the 5 volt reference reading can be monitored every time the sensors are unplugged. It is also suggested to check the ecm by disconnecting the ecm terminals making sure that the ecm pins are clean and not corroded. On extreme cases where the 5 volt reference is difficult to diagnose, the ecm pins are checked for ground and supply voltage and if proven OK, will result in replacing the ecm. Do this only if you have a wiring diagram and has the assistance of an experience online mechanic.
Tips:
When checking the ground voltage terminals on the ecm pin terminals, put the vehicle under load like your head lights to force the defective faulty ground wire to come out.
On advance set up, a good scanner can be hooked and then monitor all sensors connected to the 5 volt reference wire. With the vehicle road tested, all 5 volt reference voltage readings can be compared for changes and figure out which sensors or output loads are affected. This service should be available from any small garage if you have difficulty in finding the source of P1635 code.
If the ground voltage exceeds 0.250 volt, a practical tests can be done by checking your battery connections and all ground supplies to the engine, ecm, sensors and output loads. For a detailed assistance on this, please contact ATS.
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