Check Oil Pressure Warning Light While Idling in Bus: Here’s How to Fix It?
Two days ago, one of our buses experienced a concerning problem – oil pressure warning light while idling. This bus was relatively new, and we had just done a servicing. The driver, understandably concerned, immediately stopped and called us for guidance.
According to the driver, the oil pressure warning light appeared only when the engine was idling — whenever the RPM was low. Interestingly, the warning light disappeared when he accelerated or switched on the air conditioning.
Now, the oil pressure warning light is a serious concern, as it can signal underlying issues that could lead to catastrophic consequences, such as engine failure, if not addressed promptly.
We quickly reached out to the OEM, who asked us if there had been any noticeable loss of power in the bus. We confirmed that there was no power loss.
Since we were only about 100 kilometers from our destination, the engineers assured us that it was safe to continue the journey and advised us to bring the bus to its destination for further inspection.
Upon arrival, we diagnosed the issue, and fortunately, it turned out to be a trivial problem that was resolved within an hour.
Before I dive into the specifics of what happened with our bus, let’s first take a moment to understand the significance of the oil pressure warning light and what it indicates.
What Does the Oil Pressure Warning Light Mean?
The oil pressure warning light is a critical indicator on your bus’s dashboard. When the red, gravy boat like symbol is illuminated, it signals a potential issue with the engine oil pressure.
Oil is essential for lubricating the engine’s moving parts, reducing friction, and preventing overheating. If the oil pressure warning light comes on, it typically means that the oil pressure is too low to lubricate the engine properly.
The check oil pressure warning light indicates that there might be issues with your oil level, filter, or oil pump.
Here are some possible causes:
- Low Oil Level: One of the most common reasons for the light to appear is a low oil level. If the engine oil is insufficient, it can’t maintain the proper pressure, causing the light to turn on.
- Faulty Oil Pressure Sensor: Sometimes, the problem isn’t with the oil itself but with the sensor that monitors the oil pressure. A malfunctioning sensor can trigger the warning light even if the oil pressure is normal.
- Clogged Oil Filter: A clogged or dirty oil filter can restrict the flow of oil, causing a drop in oil pressure and triggering the warning light.
- Viscosity of Oil: The type of oil used in your bus’s engine can also play a role. If the oil is too thick (due to cold weather, for example), it may not circulate properly, leading to low oil pressure.
- Oil Pump Failure: The oil pump is responsible for circulating oil throughout the engine. If it’s failing or not working efficiently, the oil pressure warning light can come on, indicating that the engine isn’t getting the lubrication it needs.
Should You Take the Oil Pressure Warning Light Seriously?
Absolutely! The oil pressure warning light should always be taken seriously. When this light illuminates on your bus’s dashboard, it indicates a potential problem that could lead to significant engine damage if left unaddressed.
While some issues that trigger the oil pressure warning light might be relatively minor, such as a low oil level or a faulty sensor, others can be much more serious, like a failing oil pump.
Regardless of the cause, it’s essential not to ignore the warning. Prolonged driving with low oil pressure can lead to catastrophic engine failure, potentially leaving your bus stranded and incurring high repair costs.
Why Does the Oil Pressure Warning Light Appear While Idling?
The oil pressure warning light can often appear when idling and in low RPMs when the oil pump isn’t operating as efficiently as it should.
Oil pumps are positive displacement pumps, meaning they move a specific volume of oil depending on the engine’s RPM. As the RPM increases, the pump’s output also increases, ensuring a steady flow of oil throughout the engine.
However, over time, the internal components of the oil pump, such as the gears or rotors, can wear down. As these parts wear, they create larger spaces or “clearances” between them. These increased gaps make the pump less efficient, reducing its ability to push oil through the engine effectively.
At low RPMs, such as when the engine is idling, the oil pump operates at a reduced speed. If the pump’s efficiency has decreased due to wear, it may struggle to maintain the necessary pressure to ensure proper lubrication of the engine’s components.
This can trigger the oil pressure warning light on the dashboard, alerting the driver to the potential issue. The oil pressure warning light while idling is often a sign that the pump isn’t generating enough pressure to keep the engine properly lubricated at low speeds, which could result in engine damage if not addressed promptly.
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What to Do if the Oil Pump has Clearances?
If your oil pump has developed increased clearances due to wear, it can cause the oil pressure warning light to appear, especially while idling. One way to mitigate this issue is by using thicker oil.
Thicker oil, or higher-viscosity oil, can help compensate for the reduced efficiency of the pump by improving its ability to maintain oil pressure. The increased thickness of the oil helps fill in the gaps created by the wear in the pump’s internal components, allowing for better lubrication and more effective sealing within the oil pump.
As a result, thicker oil can help the pump maintain adequate pressure, even at lower RPMs, reducing the likelihood of triggering the oil pressure warning light while idling.
However, it’s important to note that using thicker oil is more of a temporary fix rather than a permanent solution. While it may help manage the issue in the short term, it’s crucial to address the underlying cause of the pump wear.
If the oil pressure warning light persists, it’s advisable to have the oil pump inspected and possibly replaced to prevent complete engine damage.
Self Diagnose Oil Pressure Warning Light Causes
If you encounter the oil pressure warning light on your bus’s dashboard, it’s important to perform a thorough check to identify the root cause. Here’s a step-by-step guide to help you diagnose the issue:
- Check Oil Level
Park the bus on level ground. Wait for 10 minutes to let the engine cool and then check the oil level. Top up if the dipstick shows a low oil level. - Check the Oil Filter
The first step is to check the oil filter. A clogged or dirty oil filter can restrict oil flow, leading to a drop in oil pressure. If the filter is blocked, it can trigger the oil pressure warning light. Replace the oil filter if necessary, ensuring it’s clean and free from debris. - Check the Oil Pressure Sensor
A faulty oil pressure sensor is another common cause of the oil pressure warning light. If the sensor is malfunctioning, it may falsely trigger the warning light even when oil pressure is normal. Test the sensor or replace it if needed. - Check for Wiring Issues
Inspect the wiring connected to the oil pressure sensor. Sometimes, loose, damaged, or corroded wiring can cause erratic readings or prevent the sensor from accurately detecting oil pressure. Make sure the wiring is intact, secure, and free of any visible damage. - Check the Oil Pressure
Finally, measure the oil pressure using a mechanical gauge. The pressure should typically be around 5 PSI at idle. If the oil pressure is too low, it could indicate issues with the oil pump or other internal components. Low oil pressure at idle is a sign that the pump may not be circulating oil effectively, and further investigation or repairs will be required.
Get in Touch with Your OEM and Perform an OBD Scan
While performing these checks will help identify common causes of the oil pressure warning light, it’s always best to consult with your OEM (Original Equipment Manufacturer).
Performing an On-Board Diagnostics (OBD) scan will allow for a deeper analysis of the vehicle’s systems, providing valuable data to pinpoint any underlying issues that may not be immediately visible.
Your OEM can provide you with more specific troubleshooting steps, helping to avoid unnecessary repairs and ensuring the long-term health of your bus’s engine.
Price of OBD Scan
The cost of an OBD scan can vary depending on the OEM (Original Equipment Manufacturer), but generally, it is not expensive. For our bus, we paid ₹1,200 + GST as of April 2025. In return, the scan provides a comprehensive diagnostic report, offering valuable insights into the health of your vehicle’s engine and systems.
Considering the benefits, the cost of ₹1,200 to ₹1,500 is quite reasonable. For a relatively small investment, you gain peace of mind and, more importantly, avoid the risk of expensive engine repairs or overhauls.
When you weigh the cost of the scan against the potential cost of engine damage, it’s clear that investing in an OBD scan is a cost-effective way to protect your vehicle.
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What Happened In Our Case?
In our case, the oil pressure warning light appeared shortly after we had completed a servicing of the bus. During the service, both the oil filter and engine oil were replaced. However, the mechanic who performed the service mistakenly didn’t fit the oil filter properly, which led to the activation of the warning light.
To ensure there were no underlying issues, we performed an On-Board Diagnostics (OBD) check on the bus as a precautionary measure. Thankfully, the diagnostics showed no other issues or errors, confirming that the problem was isolated to the improperly fitted oil filter.
Once the oil filter was properly secured, the oil pressure warning light went off, and the bus resumed normal operation.
Let us know if you find this useful. If there are other diagnostic/mecganical problems you would want us to cover, please let us now in the comments.
