2003 Chevrolet Silverado 1500 4.8L No Start, Stall

Truck wiring question:

My truck won't start and after scanning for codes, I found a crank sensor fault code. I have to remove the starter to access the sensor. Tracing one of the 3 wire connection, found the IGN 12 volt signal is missing. Replaced the sensor and truck started. Next day, the truck quit again but it started right away. On my way home it quit again and won't start for good. Have I missed anything?

ATS Adviser:

On top is the ECM wiring diagram of both crank and cam sensor. The crank sensor 3 wire connectors are the IGN signal (12V), crank signal and ref low signal. However, when troubleshooting no starts, take a look also on the cam sensor which controls the fuel. It has 3 wire connectors such as 12 volt ignition feed, ref low and fuel pressure signal. You can test these 3 wires using a DVOM but focus on IGN and ref lo signals since the other sensor signals can be measured by scope only. IGN feed should read 12 volts and ref lo is ground.

Shown below is an approximate 2003 Chevrolet Silverado cam sensor wiring diagram. Red wire for cam sensor and green wire for crank sensor are both 12 volt ignition feed. Lo ref signal wire is ground signal.

For more details, you can get a complete wiring diagram of this vehicle from most parts store when you buy parts or get it FREE online when you join ATS.

ATS Wiring TIP:

A quick way to test these sensor's 3 wire connectors for open is to wiggle it and see if you can make the IGN or ref lo voltages comes out. Also, if you watch the voltage reading and the voltage change while you are wiggling the wires, you will find the problem.


I found the problem! I hooked up an ohmmeter to test continuity on the ref lo wire and it was open. When I wiggled it and cranked the engine at the same time, it started. Looking at the cam wiring, it was barely connected by 2-3 strands of wires. Replacing this vref cam wire fixed the problem. Thanks!

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