No twelve Volt reference from PCM to crankshaft sensor

Tiny
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  • MEMBER
  • 2003 CHEVROLET AVALANCHE
  • 5.3L
  • V8
  • 4WD
  • AUTOMATIC
  • 170,000 MILES
Crank, no start. Replaced crankshaft sensor, camshaft sensor, ignition switch, and PCM. Checked all three wires from PCM to end of crankshaft sensor connector for continuity and all are good. I have "peeled" back some insulation from twelve volt green wire coming immediately out of PCM and can use a jumper wire from hot post of battery to the wire and it will immediately start. Any ideas what is going on? Thanks in advance for any help.
Tuesday, January 9th, 2018 AT 4:39 PM

15 Replies

Tiny
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Sensor signals are usually only 5 volts. Check all of your PCM fuses, they are the PCM 1 fuse in the under hood fuse block, (hot in run/start), the crank fuse (hot in start) same block, the PCM B fuse in the same block, IGN O fuse in the left I/P fuse block, (hot in run/start). I also see an IGN 1 relay that feeds that PCM 1 fuse. That relay is also under the hood. That IGN 1 relay is also fed from a IGN B fuse under the hood (hot all the time).
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Thursday, January 11th, 2018 AT 8:58 AM
Tiny
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Thanks for responding to my request for help with my Avalanche. I thought I had checked the items you suggested but just to make sure I went back and verified the things you listed were indeed to spec.

I am stumped on this vehicle. In addition to what I listed I have also checked the blue/green C1 and C1 connectors to the PCM. I removed them and checked them for full time twelve volts from the under hood fuse box as well as IGN 1 voltage (run). Also, checked the wire connectors at the blue/green PCM connectors and the pins on the PCM and all seemed to be good condition.

I am pretty much out of ideas. Now I know how people end up with 4,000 boat anchors setting in their yard. :). Any other ideas or suggestions?

I thank you very much for your help.
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Thursday, January 11th, 2018 AT 1:21 PM
Tiny
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Try a new IGN 1 relay.
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Thursday, January 11th, 2018 AT 2:52 PM
Tiny
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Went and purchased a new relay for the IGN 1 in fuse box. No change. Still no 12 volts to wire from computer to crankshaft sensor with ignition switch in run position. This is the green wire (#2 position on Blue connector to PCM). Any other ideas? Once again, thanks for your help.
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Friday, January 12th, 2018 AT 11:24 AM
Tiny
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Answer these questions: How much voltage do you have at both sides of these fuses?
1. The PCM 1 fuse in the under hood fuse block, with the key on run?
2. The crank fuse with the key on start? Same underhood block
3. The PCM B fuse in the same underhood block, with key off?
4. The IGN O fuse in the left I/P fuse block with the key on run?
5. The IGN B fuse under the hood with key off?
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Friday, January 12th, 2018 AT 3:11 PM
Tiny
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Ok. Here are the readings. I read voltage on the battery initially and it indicated 11 volts - somewhat discharged from setting and testing.

1. The PCM 1 fuse in the under hood fuse block, with the key on run? 11v/11v
2. The crank fuse with the key on start? Same underhood block 10v/10v
3. The PCM B fuse in the same underhood block, with key off? 11v/11v
4. The IGN O fuse in the left I/P fuse block with the key on run? 5v/5v
5. The IGN B fuse under the hood with key off? 11v/11v
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Friday, January 12th, 2018 AT 4:52 PM
Tiny
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Didn't mention previously, but my instrument cluster has been jacked up the last several weeks/months. First, the transmission gear indicator went out. Then the oil pressure gage started pegging out way past max all the way to the right. Then the speedometer would indicate about 30 when I was probably doing 60+. Speedometer issue was coming and going based on how cool the weather was.
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Friday, January 12th, 2018 AT 5:10 PM
Tiny
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That ign o fuse should be battery voltage, too. That is fed from the ignition switch. I see the tbc ign o fuse is also fed from the ignition switch and is spliced to the same wire that feeds that ign o fuse fuse so check the voltage at that tbc ign o fuse. Same left I/p fuse block. If it's only 5 volts also, check the white wire right at the ignition switch again for voltage with the key on run and if it's still 5 volts there it appears you have a bad ignition switch.
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Friday, January 12th, 2018 AT 5:28 PM
Tiny
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Will do and I'll report back. Thanks.
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Friday, January 12th, 2018 AT 5:32 PM
Tiny
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Well - bad news or good news - depending on how you look at it. I hooked up battery charger this weekend and charged the battery - just to make sure. The IGN 0 and the TBC IGN 0 both read 11 volts. I checked three times just to make sure. Don't know if I wasn't getting a good connection previously or what. Anyway, all is well with those readings.
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Monday, January 15th, 2018 AT 4:00 PM
Tiny
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For one thing after charging the battery, all of those fuses should be at least 12 volts.
Anyhow, do you finally have the 5 volts going to the crankshaft position sensor from the pcm or not?
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Monday, January 15th, 2018 AT 4:51 PM
Tiny
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No. Sure don't. No voltage to crankshaft sensor.
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Monday, January 15th, 2018 AT 5:11 PM
Tiny
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It appears then you have a faulty pcm.
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Monday, January 15th, 2018 AT 5:13 PM
Tiny
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Well I thought the same thing, but have already changed out the pcm. Had it flashed to match the old one and it still is doing the same thing. So I have an extra PCM now.
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Monday, January 15th, 2018 AT 5:16 PM
Tiny
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Which color wire are you testing for voltage to the crankshaft position sensor and are you testing with the key on run, key off or key on start cranking the engine over?
Is there any security issue preventing that engine from starting? Is there any security light remaining on past bulb check or flashing?
Is the check engine light remaining on or flashing/
Have you pulled any codes from the pcm?
Does the check engine light at least come on for bulb check, when you first turn the key to run?
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Monday, January 15th, 2018 AT 6:09 PM

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