* Instrument Cluster: The fuel gauge and coolant temperature gauge are both controlled by the instrument cluster. A faulty instrument cluster, a bad connection to the cluster, or a problem within the cluster's circuitry could explain both gauges not working.
* Body Control Module (BCM): The BCM is a central computer that controls many electrical functions, including DRLs. A faulty BCM is a strong possibility if all three systems are malfunctioning. A failing BCM often manifests with multiple seemingly unrelated electrical problems.
* Wiring Harness Issues: A break, short, or corrosion in the wiring harness affecting the power or ground for these circuits is also possible. This is especially likely if the affected components are located in different parts of the car. Inspect wiring harnesses, paying close attention to areas that experience vibration or movement (engine bay, under the dash). Look for chafing, broken wires, or corrosion.
* Grounding Problems: A poor ground connection can affect multiple electrical systems. Check the main ground points in the engine bay and chassis. Poor ground connections can cause erratic operation or complete failure of various components.
* Power Supply Issue: While you've checked fuses, a faulty wire leading *to* the fuse or a problem with the power distribution circuit itself could be the culprit. It's less likely if all three are down, but worth considering.
Troubleshooting Steps:
1. Visual Inspection: Carefully inspect all wiring related to the fuel gauge, coolant temperature sensor, and DRLs for any signs of damage.
2. Check Ground Connections: Clean and tighten all ground connections you can easily access.
3. Instrument Cluster Test (If Possible): If you have access to a diagnostic scanner, it might be possible to test the instrument cluster's functionality independently.
4. BCM Test (Requires Scanner): A diagnostic scanner is needed to check the BCM for fault codes. This would give you a much clearer indication of the problem.
5. Wiring Diagram: Obtain a wiring diagram for your 1998 Chevy Malibu. This will show the circuits for each component and help you trace the wiring to identify any breaks or shorts. These diagrams are available online from various sources, often for a small fee.
6. Professional Diagnosis: If you're not comfortable working with automotive electronics, take your vehicle to a qualified mechanic. They will have the diagnostic tools and expertise to pinpoint the problem quickly and accurately. A generic scan tool might not catch this since these seem unrelated.
Because all three systems are affected, the problem is most likely a central issue like the BCM, a major ground fault, or a widespread problem with the vehicle's wiring harness. A professional scan and inspection are strongly recommended.
