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Brad
Brad, Jeep Dealership Tech
Category: Jeep
Satisfied Customers: 7507
Experience:  19 Yrs Chrysler/Dodge/Jeep. ASE Master (L-1) Certified
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I have a 2009 Jeep Liberty. The top stoplight works but not

Customer Question

Hi! I have a 2009 Jeep Liberty. The top stoplight works but not the two on the left and right. On the driver's side left I removed the taillight assembly and disconnected the plug. Seems like there is a constant 8 volts to the two terminals (upper left two, hot, ground) but only perhaps a 1 volt rise when I step on the brake
Submitted: 1 year ago.
Category: Jeep
Expert:  Brad replied 1 year ago.

Good morning...

I have attached the brake wiring diagram. The TIPM which is the fuse box under the hood supplies 12v to the brake lights and if it only has 8v then you likely have a bad TIPM.. Do you know what codes are in the TIPM, this will require a scantool..

Expert:  Brad replied 1 year ago.
Customer: replied 1 year ago.
I hooked up a CanOBD2 to the diagnostic port (if that is what it's called) and it read the protocol, established a link, but said there were no DTC's or freezeframe data (approximate quote here) in the system. I did disconnect the negative battery cable for a moment previously. Driving it around the block did not populate any codes. The passenger's side voltage is close to the driver's side, only difference I think is that there is no standing voltage, and maybe 5-6 volts if I press on the pedal. Now, the running light comes on if I press the brake pedal. Thought I'd mention that.
Expert:  Brad replied 1 year ago.

You have a code reader and you will need a scantool such as the WiTech I use here at the dealership to retrieve the codes from the TIPM..

Customer: replied 1 year ago.
Can't I verify this by disconnecting a fuse or wire to measure the voltage? The flow comes out of the TIPM someplace, right? Shouldn't I be able to measure the voltage from that point?
Expert:  Brad replied 1 year ago.

Did you get the wiring diagram I sent? If you wanted to you can remove the TIPM and disconnect C7 and see if pin 47 has 12v or 8v. If it doesn't have 12v then you likely need a new TIPM but the proper way to diagnose this issue is with a scantool..

Customer: replied 1 year ago.
TIPM is off. C7 is a green connector? How can I identify pin 47 or 49
Customer: replied 1 year ago.
Ok, giving up on getting more info. I have ordered a TIPM. A little more information would have helped...
Customer: replied 1 year ago.
To anyone reading this, the fix was to replace ALL the bulbs, even the ones that were not burnt out, even though none of them were actually "bad" when measured or tested against a battery. I took this to a friend with years of experience who insisted we go out and buy all six, each side and replace them. It worked. The bulbs were 12 bucks.
Expert:  Brad replied 1 year ago.

If that is the case then you should have 12v at the light connector and I wouldn't have had you test the TIPM. You have to understand I'm not there testing and I depend on you the customer to give me good readings.. Yes if you had tested 12v at the connector which you have since the bulbs are working then I would have had you replace the bulbs..

Glad I could help and thank you for the positive rating,

Brad

Customer: replied 1 year ago.
I appreciate that you tried to help. I think the point here however is that testing was misleading -- and not in itself conclusive. The point is that the modern bulb design (Which skimp on raw materials and have less electrical connection surface area) plays a part in the operation of the system. In future I think your first advice to clients should be to replace ALL bulbs on both sides as cheap and quick first step. Put yourself in the position of a customer who is trying to troubleshoot this without immediately being referred to a dealership or other expensive testing facility. Some more explanation would have been helpful -- more than short replies, explanations that explain a bit more of the system. It is true that you are not here, that's why this can't be done without some exposition. I came here hoping to purchase a little experience and insight. I hope you can take the constructive comments to heart.
Expert:  Brad replied 1 year ago.

Your your referring to the test I asked for you to do as in testing for 12v to the bulb as misleading I have to say I disagree.. If the bulb will not light up the very first test is to check for 12v and ground. You said you have 8v and rises to 9v then you have a voltage supply issue, but if you replaced the bulbs and it worked then you do have 12v at the bulb and not the 8v you had first said. You may have had a poor connection which showed 8v, but either way it fixed and I appreciate the positive rating so I;m compensated for my time..

Have a great weekend,

Brad