Test light for checking short circuit?

[Noname]

Iv been trying to figure out a p0153 code for a while now. 2005 jeep LJ. Using a tester light I connected the alligator clip to my positive battery terminal and then probed the positive battery cable and the light turns on ever so slightly and then dims down and off completely within 2-3 seconds. When I touch the probe to the negative battery terminal it turns on strong and bright.

I’m wondering if this indicates I have no shorts at all in my wiring harness? Because from what I read and watched in tutorials, if you clip the positive terminal and touch the positive cable the tester light will illuminate indicating a short somewhere and then you proceed with removing fuses and unplugging the pcm, ground points, o2 sensors etc etc until that tester light turns off.

Any help is appreciated. Im confused why my tester light isn’t turning on after touching both positive leads and if it means I have no short circuits or im doing something wrong with this diagnosis trick

 

[Chris]

Iv been trying to figure out a p0153 code for a while now. 2005 jeep LJ. Using a tester light I connected the alligator clip to my positive battery terminal and then probed the positive battery cable and the light turns on ever so slightly and then dims down and off completely within 2-3 seconds. When I touch the probe to the negative battery terminal it turns on strong and bright.

I’m wondering if this indicates I have no shorts at all in my wiring harness? Because from what I read and watched in tutorials, if you clip the positive terminal and touch the positive cable the tester light will illuminate indicating a short somewhere and then you proceed with removing fuses and unplugging the pcm, ground points, o2 sensors etc etc until that tester light turns off.

Any help is appreciated. Im confused why my tester light isn’t turning on after touching both positive leads and if it means I have no short circuits or im doing something wrong with this diagnosis trick

The behavior of your test light when connecting to the positive battery terminal and the positive cable can give you some clues.

First, when you clip the test light to the positive battery terminal and probe the positive cable, the light dimming and then going out could indicate a few things:

Voltage Drop: If there’s a weak connection or corrosion on the positive cable or terminal, it could cause a voltage drop, leading the light to dim. This might not necessarily indicate a short circuit but could mean there's excessive resistance in the positive lead.

Ground Reference: When you touch the probe to the negative terminal and it lights up bright, it shows that you have a good ground connection. This suggests your ground side is fine, but the fact that your test light doesn’t stay lit on the positive side suggests there’s likely no short, but possibly an issue with the connection.

In summary, your observations seem to lean towards the fact that you might not have a short circuit in your wiring, especially since the light stays bright when probing the negative terminal. However, since you're getting a dimming light when probing the positive battery cable, it's worth checking the integrity of that connection and the cable itself.

Consider taking these steps:

• Inspect and clean the positive terminal and battery cable for corrosion.
• Ensure tight connections at both the battery and the starter or distribution points.
• If you have a multimeter, measuring the voltage at various points could give you more clarity about where any issues might be.

If you’re still seeing the P0153 code after these checks, it might be worth looking into the O2 sensor wiring or the sensor itself as it might be complying with your test light results but causing the code to activate.

Hope this helps clear up some of your confusion! Keep us updated on your findings.

 

[TJ Jim]

Iv been trying to figure out a p0153 code for a while now. 2005 jeep LJ. Using a tester light I connected the alligator clip to my positive battery terminal and then probed the positive battery cable and the light turns on ever so slightly and then dims down and off completely within 2-3 seconds. When I touch the probe to the negative battery terminal it turns on strong and bright.

I’m wondering if this indicates I have no shorts at all in my wiring harness? Because from what I read and watched in tutorials, if you clip the positive terminal and touch the positive cable the tester light will illuminate indicating a short somewhere and then you proceed with removing fuses and unplugging the pcm, ground points, o2 sensors etc etc until that tester light turns off.

Any help is appreciated. Im confused why my tester light isn’t turning on after touching both positive leads and if it means I have no short circuits or im doing something wrong with this diagnosis trick

https://www.obd-codes.com/p0153

 

[TJ Jim]

Not sure what you’re trying to accomplish with the tester, but you may be going in the wrong direction.
https://www.obd-codes.com/p0153

 

[FPGT72]

A very useful tool for checking shorts and opens is a power probe, I don't think it will help with your issue, but if you're playing with cars it falls into the group of tools called where have you been all my life.

PS. Get the real one, they are spendy but well worth it.

 

[Noname]

The behavior of your test light when connecting to the positive battery terminal and the positive cable can give you some clues.

First, when you clip the test light to the positive battery terminal and probe the positive cable, the light dimming and then going out could indicate a few things:

Voltage Drop: If there’s a weak connection or corrosion on the positive cable or terminal, it could cause a voltage drop, leading the light to dim. This might not necessarily indicate a short circuit but could mean there's excessive resistance in the positive lead.

Ground Reference: When you touch the probe to the negative terminal and it lights up bright, it shows that you have a good ground connection. This suggests your ground side is fine, but the fact that your test light doesn’t stay lit on the positive side suggests there’s likely no short, but possibly an issue with the connection.

In summary, your observations seem to lean towards the fact that you might not have a short circuit in your wiring, especially since the light stays bright when probing the negative terminal. However, since you're getting a dimming light when probing the positive battery cable, it's worth checking the integrity of that connection and the cable itself.

Consider taking these steps:

• Inspect and clean the positive terminal and battery cable for corrosion.
• Ensure tight connections at both the battery and the starter or distribution points.
• If you have a multimeter, measuring the voltage at various points could give you more clarity about where any issues might be.

If you’re still seeing the P0153 code after these checks, it might be worth looking into the O2 sensor wiring or the sensor itself as it might be complying with your test light results but causing the code to activate.

Hope this helps clear up some of your confusion! Keep us updated on your findings.

O2 sensor has been replaced with a brand new ngk. PCM has been replaced with a brand new one a couple years ago. Fixed a vacuum leak. Checked where the exhaust meets the manifold flange and tightened the bolts.

Was trying to cancel out a short circuit issue with the tester light but it won’t stay on for me to remove the common ground point connection for my o2 sensors, unplug the pcm plugs, unplug the 02 sensor plug, remove fuses, wiggle wires etc etc thats why Im wondering why the tester light doesnt stay illuminated when attaching both leads to positive. If I could unplug the pcm and the tester light still doesnt turn off it cancels out the computer, and also the signal and heater circuits to my 02 sensor. Would leave me to only deal with ground.

Aside from that the only other thing I have yet to do is plug the exhaust and smoke the system to see if there’s an exhaust leak anywhere. Thats the only thing I haven’t done yet. Just wondering about this tester light situation currently

 

[Chris]

O2 sensor has been replaced with a brand new ngk. PCM has been replaced with a brand new one a couple years ago. Fixed a vacuum leak. Checked where the exhaust meets the manifold flange and tightened the bolts.

Was trying to cancel out a short circuit issue with the tester light but it won’t stay on for me to remove the common ground point connection for my o2 sensors, unplug the pcm plugs, unplug the 02 sensor plug, remove fuses, wiggle wires etc etc thats why Im wondering why the tester light doesnt stay illuminated when attaching both leads to positive. If I could unplug the pcm and the tester light still doesnt turn off it cancels out the computer, and also the signal and heater circuits to my 02 sensor. Would leave me to only deal with ground.

Aside from that the only other thing I have yet to do is plug the exhaust and smoke the system to see if there’s an exhaust leak anywhere. Thats the only thing I haven’t done yet. Just wondering about this tester light situation currently

Regarding your test light situation, if it doesn’t stay illuminated when probing the positive battery cable, and considering that you have made other checks (like grounding and replacements), it suggests you might not have a direct short to ground, especially since the light illuminates strongly when touching the negative terminal.

Here are a few more things you can consider regarding the test light and your troubleshooting approach:

Inspect for Voltage Drop: As previously mentioned, a dimming light could indicate excessive resistance or a poor connection. It’s a good practice to inspect for any frayed wires, bad connectors, or corrosion at the terminals—especially at the battery, starter, and any junction points along the positive cable.

Test with a Multimeter: If you have access to a multimeter, use it to check continuity and voltage at various points in your system. This can help you identify where there might be a drop in voltage or resistance.

Ground Connections: Since your test light behaves differently when touching the negative and positive terminals, make sure all ground connections related to the O2 sensor and PCM are clean and secure. A weak ground can cause strange issues.

Read Any Additional Codes: Sometimes, there can be multiple codes that could help you zero in on the issue. Make sure to check for any additional codes besides P0153.

Exhaust System Check: Finally, your idea to smoke test the system for exhaust leaks is a solid one! A leak upstream from the O2 sensor could lead to incorrect readings and cause the P0153 code.

It seems like you're on the right path. Just remember, diagnostics can sometimes be a process of elimination, so continue to methodically check each part of the system. Keep us posted on your findings!

 

[Noname]

Regarding your test light situation, if it doesn’t stay illuminated when probing the positive battery cable, and considering that you have made other checks (like grounding and replacements), it suggests you might not have a direct short to ground, especially since the light illuminates strongly when touching the negative terminal.

Here are a few more things you can consider regarding the test light and your troubleshooting approach:

Inspect for Voltage Drop: As previously mentioned, a dimming light could indicate excessive resistance or a poor connection. It’s a good practice to inspect for any frayed wires, bad connectors, or corrosion at the terminals—especially at the battery, starter, and any junction points along the positive cable.

Test with a Multimeter: If you have access to a multimeter, use it to check continuity and voltage at various points in your system. This can help you identify where there might be a drop in voltage or resistance.

Ground Connections: Since your test light behaves differently when touching the negative and positive terminals, make sure all ground connections related to the O2 sensor and PCM are clean and secure. A weak ground can cause strange issues.

Read Any Additional Codes: Sometimes, there can be multiple codes that could help you zero in on the issue. Make sure to check for any additional codes besides P0153.

Exhaust System Check: Finally, your idea to smoke test the system for exhaust leaks is a solid one! A leak upstream from the O2 sensor could lead to incorrect readings and cause the P0153 code.

It seems like you're on the right path. Just remember, diagnostics can sometimes be a process of elimination, so continue to methodically check each part of the system. Keep us posted on your findings!

Very good very good thanks for the help!

 

[steelhd]

You need a multimeter instead of a test light.

 

[TJ Jim]

thats why Im wondering why the tester light doesnt stay illuminated when attaching both leads to positive.

This part confuses me? Positive to positive does not give you a difference of potential so you will not see a signal. You must go from positive to negative to get a difference in potential and illuminate your test light. Check you ground on the block and make sure it is secure and clean. Put one end of your test light to the grounds and the other to your positive battery terminal to light your test light.

Why are you putting both ends of your test light on the positive cable?

 

[ItchyDong]

This part confuses me? Positive to positive does not give you a difference of potential so you will not see a signal. You must go from positive to negative to get a difference in potential and illuminate your test light. Check you ground on the block and make sure it is secure and clean. Put one end of your test light to the grounds and the other to your positive battery terminal to light your test light.

Why are you putting both ends of your test light on the positive cable?

This made my brain hurt too.

 

[KennethS]

This part confuses me? Positive to positive does not give you a difference of potential so you will not see a signal.

Agreed. The only way a test light will illuminate when connected like that is if there is a resistance in the positive wiring between the points where the test light is connected that is larger than the test light resistance.