stilllearning6

2003 Tahoe 5.3 L, Flex:
Both the tach and the fuel gauge jumped to off the index gauge max on the same drive.

First, I noticed that the fuel gauge was reading correctly just after a fill-up. Good. Parked car at home.
Next day, started vehicle and saw that fuel gauge was reading excessively high. A little too high but not off the chart.
Hmm. What's happening? Just a little off at this time.

Started a 50 mile trip.
The tach was correctly reading rpm's at approx 1300 rpm's while highway cruising 60 mph.
Took photo 5 minutes into 50 mile trip. Tach is good; fuel gauge a little too high.
That will soon change.
As I drove the vehicle on a 50 mile trip, I saw that the fuel gauge was gradually dropping. Good.
Reached approximately "3/4 plus " full after 50 trip. Good.
However, twenty minutes into the trip, I also noticed that while highway cruising at 60 mph, the tach was now reading way too high .
It read off the chart (above 6000 rpms ) the tach was suddenly over maxed.
I suspected a poor tach connection : cable or wiring issue?
Turned engine off 20 minutes.

Perhaps things will reset??

Upon restarting, the fuel gauge was now excessively buried to the far right , way over the full index.
Just prior to turning off engine after the 50 mile trip, it was showing 3/4 full. Dramatic change to bad.
Perhaps a bad electrical connection in the fuel gauge circuit?

Also, the tach was showing rpm's way too high upon restarting. Guessing at least 6000.
As I increased engine speed while parked, the tach would increase to go way off the chart.
Tach returned to a minimum of 4600 rpm while still at idle.
It seemed to be overstating the actual rpm .

Both issues appeared during the same trip.
The fuel gauge was the first to show indications of a fault, tach would soon follow.
I believe that the fuel gauge circuit may have a faulty ground causing super high full reading.
Since the tach is also experiencing crazy readings, I am wondering if the two circuits share a common grounding terminal that might be faulty.

The Tahoe fuel sending unit sits atop the fuel tank and might require dropping the tank to access the sending unit terminals.
I did that job at Halloween and it was a nightmare. Looking to avoid that procedure.

I suspect/hoping something in the dash may be the culprit. I do not know.
Any guidance as to what might cause both tach and fuel gauge to be maxed out?

Photo below shows 5 minutes into trip, tach is still AOK, fuel gauge reads a little too high:


Below photo morning after trip: engine OFF, tach reads 4000 rpm, Fuel gauge reads almost Full . But, engine is OFF. All should read zero.

Gumby22

The gauge clusters in this era of GM vehicles (all of them, not just SUV’s) are known for multiple problems due to cold solder joints and faulty stepper motors, which is what moves the gauges. They can be repaired if you’re skilled at soldering, otherwise you can send it out for repair.

All the gauges and indicators are logic controlled by the cluster - it receives necessary information from the PCM, BCM and other modules via the class 2 data network and performs tasks accordingly. The tach and fuel gauge only malfunctioning indicates there may be a short in the wiring harness to the cluster, but your best chance of determining if it’s the cluster or not is by having a shop check the IPC for codes and check gauge/light function with a scan tool.

You can visually inspect the wiring harnesses under the dash and in the engine bay for areas that have rubbed through and may be grounding out or shorting together. The next step would be to remove the cluster and check power/ground inputs and signal feeds at the IPC connectors.

stilllearning6

Gumby, thank you for feedback.
I ordered $32 cluster repair kit which includes 7 stepper motors and solder sucker and heat gun.
I needed to solder the weak PRNDL solder joint associated with my failed PRNDL pixels , so the value was there for me.

Yes, it might merely be a shared rubbed common wiring harness , yet I am leaning to both stepper motors as culprits in spite of both appearing within same trip, not at exact same time.

Plus, after sitting overnight again, both came back to normal within 3 minutes but not at same time.
I will wait for good weather to start this project.

Gumby22

It’s not too difficult to repair the cluster - it just takes patience.

Before removing the gauge needles, put a piece of masking or painters tape on the cluster face and mark the default positions with a marker.