I'm terrible at figuring out a pattern with these flashing lights. Can someone help me diagnose please? T.I.A.
91 2.5 5 speed, no A/C,
91 2.5 5 speed, no A/C,
Help reading check engine codes
- Thread starter Maxamy
- Start date
12, 33, 14, 15, 55. 14 and 15 are the only two worth thinking about.
14: MAP sensor circuit open or shorted; voltage too low
15: No speed/distance sensor signal
To have both of them throwing codes I wonder if you have an issue with the sensor ground circuit or maybe the PCM’s power supply. I think both of those are provided a 5V power supply, but I’d need to dig into the FSM again to refresh my memory.
14: MAP sensor circuit open or shorted; voltage too low
15: No speed/distance sensor signal
To have both of them throwing codes I wonder if you have an issue with the sensor ground circuit or maybe the PCM’s power supply. I think both of those are provided a 5V power supply, but I’d need to dig into the FSM again to refresh my memory.
Is that the turn key on-off three times method? I have done that on my LJ but didn’t know it worked on YJs. I thought I would have to get an OBD1 reader if it ever threw codes.
Well I think it works. I was just told by a local mechanic that this method only works on vehicles prior to 1986 but I think he's wrong. There's a chart online to determine what the flashes mean I just am always unsure of what I'm seeing. The above post diagnosed mine so apparently it's a thing
So, how would I determine which problem? Check for 5V at the sensor? I know where the MAP is but where is the Speed distance sensor? is that under the Jeep on the transmission? would I check for 5V there as well?
It definitely works, this process of checking codes is straight out of the factory service manual.
So I was wrong about the power supply - the PCM provides 8V power to the to the speed sensor on circuit K7. The PCM provides 5V power to the MAP sensor on circuit K6.
They both share the sensor ground from circuit K4.
There are a bunch of other sensors utilizing the K4 ground circuit, and they all originate from one splice, so I doubt it's a grounding problem, because the MAP and VSS are on their own separate legs of ground.
To test the MAP:
Probe terminals A and B with a multi meter and observe voltage. Should find 4-5V with engine OFF and key ON. Voltage should drop to 1.5-2.1V with the engine running, at warmed up idle.
Testing the voltage at the PCM would verify the same voltage at the sensor and the PCM, to help make sure the wires are good.
For testing the VSS, the FSM just recommends following the procedure in the Powertrain Diagnostics manual using a DRB. So you're kinda out of luck on that one. You can at least test the connector terminals to verify the 8V, and confirm you have a 5V speed signal at the PCM and instrument cluster. These would both be with the ignition on.
This is awesome! Thank you so much of your help... I appreciate you taking the time... I will do these and report back.