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:
  • 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!


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