A technician was facing a strange issue with a 2015 Toyota Land Cruiser with a 5.7L V8 engine. It was experiencing what he described as a strange loss of power output. Motor Age Technical Editor Brandon Steckler jumped in to help with the diagnosis.
Steckler thought it was a straight-forward issue, but was faced with helping the young tech obtain the needed data. You can get reacquiainted with the Toyota case's details here.
Here are the four options Steckler offered. Which did you choose?
- Replace PCM for erratic internally shorted 5V reference
- Monitor 5V reference circuit at PCM, with amp probe
- Rewire all the 5V reference circuit feeds on the vehicle
- Replace CKP/CMP sensors for intermittent 5V ref short to ground
For those of you who chose answer No. 2, congratulations. An amp probe place around the 5V reference wire of the PCM would’ve shown an increase in current each time the sensor signals failed.
Careful inspection prior to more pinpointed testing of the wire harness would’ve revealed a poorly secured harness. The connector pigtail for the fuel tank pressure sensor allowed the 5v reference wire to melt on the exhaust pipe and short the signal to ground, pulling it low and causing the stall (See the image).
Although a faulty PCM could cause this issue, it wouldn’t be wise to condemn a computer without eliminating external faults. Rewiring all existing 5V reference circuits would’ve solved the issue but would be a tremendous investment in time and not an efficient use of that time. Replacing the CMP/CKP sensors is not going to solve this issue but could be the cause of the stalling symptom. Without evidence to support the sensor failure, it would simply be a guess and not very professional to conduct analyses like that.
Motor Age Technical Editor Brandon Steckler presents a new case for the Data Doesn't Lie each month.
