5V Reference Circuit

🚗 2007 Cadillac Escalade 6.2L

• Car would intermittently stall on the road.
  • Sometimes it would start, sometimes would refuse.
• Customer’s tech has pulled ECM codes that have been complaining about 5V reference (P0641) and CMP sensor circuit.
• CMP sensor has been replaced.
  • CMP code yet still remained. Sometimes 5V code would also pop up.
• ECM has been replaced and reprogrammed with same results.
• After much testing, customer’s technician started cutting wires and jumping them between ECM and CMP, claiming there was no continuity.
• Then, customer decided to introduce this brat to me, hoping that my story will have a positive ending for a change.
• Long story short, before I get to the point of a case study, I had to rewire the previously cut wires back to the CMP sensor, and replace ECM connector terminal for CMP 5V due to damage.
  • ECM connector terminal was shamelessly abused by a thick testing lead that widened it which broke connectivity between ECM’s connector and the ECM.
  • I use a thin test probe/needle to ‘drag test’ all suspected terminals.
• After fixing secondary diagnostics-caused issues I had start tackling the original complaint with intermittent no start and stalling.

🩺 Diagnosis

• Codes (from ECM)
  • P0315 Crankshaft Position (CKP) system variation not learned (Special Functions ➯ CKP relearn, after other codes are fixed)
  • P0606 Control module internal performance
  • P0641 5V reference 1 circuit
  • P2122 Accelerator Pedal Position (APP) (sensor 1) circuit low voltage
  • P0107 Manifold Absolute Pressure (MAP) sensor circuit low voltage
  • P0452 Fuel Tank Pressure (FTP) sensor circuit low voltage
  • P0532 A/C refrigerant pressure sensor circuit low voltage
• Which code to troubleshoot first?
  • What is common between all these codes? All these sensors are connected to the same 5V Reference 1 circuit.
  • So, this is where I should start my search.
• ECM ➯ Live Data ➯ Ignition
  • 
  • This shows that 5V Reference 1 Circuit is pulled to ground (should be 5V obviously).
• Diagram of a 5V Reference Circuit
  • 
• The possibilities are
  • One of the sensors is faulty
  • 5V reference circuit leading to the sensors is shorted to ground somewhere
• Where should I start?
  • God gave me a thought, and I remembered that the car was running fine in my shop until the moment I started moving. After I’ve moved for like a foot it stalled.
• So, I decided to look at Fuel Tank Pressure (FTP) sensor first, because it might have a 5V reference running near moving parts under the car. Here is what I found:
  •  
  • A few wires from a loom have been arbitrarily touching front (driver side) driveshaft!
  • One of them was 5V reference wire.
• When I’ve insulated the compromised wires with heat-shrink waterproof butt connectors, a new corrugated harness conduit, and zip-tied it away from temptation, here is what live data showed me:
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• When customer came to pick up the car, after his 10th ‘thank you so much’ I stopped counting. What a headache it has been to him!