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Discussion Starter · #1 ·
When I turn the ignition to the run position, the trans indicator on the instrument cluster panel (meter assembly) works fine. Every gear I shift to, shows up on the panel. If I shift it to "N" or "P" and start the engine, it stays stuck on that "N" or "P" light. I have already changed the A/T control module (mode sensor) and think it might be the multi-plexed indicator control unit or the powertrain control module (PCM). Any idea or thoughts would be greatly appreciated. :cry:
 

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The Range Mode Switch (RMS) sends four signals that are either +12 VDC or 0 VDC depending on the gear selection to the PCM. The PCM converts this 4 bit input into Class 2 serial data and sends it to the Multiplexed Indicator Control Unit (MICU) which decodes it and selects the correct instrument panel gear indicator lamp to illuminate. Since all the gear selection lamps work properly when the engine is not running the MICU has to be working properly. It seems that once the engine is started the Class 2 serial data is no longer being updated. The only apparent difference in operation of the MICU between engine running and not running is the power source.

It is possible the Alternator output voltage is too high or there is too much AC hash in the Alternator output which is causing a disruption in the Class 2 serial data. Step one is to ensure the voltage across the battery terminals with the engine running is not greater that 14.5 VDC.
 

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Discussion Starter · #3 ·
The voltage across the battery terminals with the engine running is 14.3 VDC. Any other ideas on what it might be or that I should check? :shock:
 

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The next step is to disable the Alternator by removing the serpentine belt and starting the engine to see how the gear lamps respond with the engine running on battery power only. The expected result is that the lamps should operate correctly and the Battery Icon on the instrument panel should illuminate indicating the Alternator is not working. The engine temp will slowly rise at idle but will not overheat unless left running for a long time. If the gear lamps still do not work correctly then????.
 

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Discussion Starter · #5 ·
Tried to see if the indicator light would work before I started it and I had no light at all. It was 91 degree outside and I didn't disconnect the serpentine belt yet. I then disconnected the battery and cleaned the connections with electrical cleaner going to PCM and Multifunction switch and still no light. Could it be a connection problem? And what connection could it be?
 

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If the lamps no longer work with the engine not running then there is no need to disable the Alternator as this is a different symptom than you originally reported. Check to see if your backup lamps are working, the fuse that powers them also powers the transmission Range Mode Switch.
 

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Discussion Starter · #7 ·
Hey Buster28, I appreciate all your help. The reverse lights are working in the run position, but still no indicator lights. The mode switch is new, so maybe check the power going to it? Which wires power the mode switch?
 

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Discussion Starter · #8 ·
Ok, I jacked up the front driver side so that I could check the mode switch for power and put the ignition switch to the run position and the indicator light was on and working. Started it up and everything is working fine and the alternator is putting out 14.01 volts. What the heck is going on with this? It has to be a broken wire, or a bad connection plug somewhere. I know it's fixed for now, but it's going to do it again (maybe tomorrow). What should I check next?
 

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Hard to determine exactly what is going on. However, if the backup lamps illuminate the RMS switch is receiving power. The same +12 VDC that generates the four wire gear selection code powers the backup lamps through a different set of contacts on the RMS.
 

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Discussion Starter · #10 ·
So the problem is between the rms and the pcm. What wire and connector should I check at the pcm. Could it also be a bad ground?
 

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It is unlikely the problem is between the RMS and the PCM as there are 4 wires involved. If one or more wires are open an invalid gear selection code should be generated causing the CEL to illuminate and DTC P0705 (RMS Illegal Position) to be set. Further, the transmission defaults to Drive range with maximum line pressure which causes harsh shifts to occur when this DTC is set. Accordingly, if your transmission is shifting properly the problem is between the PCM and the MICU which is single wire serial data or between the MICU and the instrument panel. Check to ensure the chassis ground point for the MICU is clean and tight.

The Winter and Power lamps are also controlled by the MICU, if these illuminate when the corresponding switch is activated the serial data bus and MICU are working.
 

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Discussion Starter · #12 ·
Ok, it went back to the original problem working in run position and engine not started. I disconnect serpentine belt and indicator light wouldn't move but battery light was on. Installed belt and put in run position without starting and the indicator lights worked. Started engine and it moved until it got to "N" and stayed stuck on "N". The Winter and Power lamps were not working, so I'm guessing it's the MICU or gremlins maybe? :shock: I also cleaned the ground for the MICU.
 

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Because the Winter/Power lamps quit working it indicates this problem has nothing to do with the RMS or the A/T shift indicator module. Further, since the "N" lamp remained illuminated it indicates the MICU is receiving power because the power for the A/T shift lamps comes from the MICU and there is only one +12 VDC input to the MICU.

The signal to illuminate the Winter/Power lamps and the A/T shift indicators in contained in the serial data sent to the MICU from the PCM. I believe the problem involves the serial data bus and not the MICU. The only way to check on the functionally of the serial data bus is to hook up a scan tool to the diagnostic port and monitor real time engine parameters to see if they are being updated when this anomaly occurs.
 

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Discussion Starter · #14 ·
When the indicator lamps are not working, I can push the Winter/Power switch and hear the transmission adjust but the lamps don't work. Where is the Class 2 serial data cable located on the PCM?
 

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There is no dedicated cable, it is a single Orange/Black wire that connects to the Blue ECM/PCM connector E21 Pin 58 to MICU connector B26-11 via Green left fender connector H5-7. It is also connected to Data Link Connector Pin 2
 

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The ECM/PCM on a 01/02 Rodeo is located on the left side behind the air filter box, I assume is it the same on a 00. There are two 80 Pin connectors attached, (E22) and (E21). E22 is closest to the fender. Connector H5 is Green and is adjacent to the ECM/PCM under the fender lip. The MICU is located at the rear of center console under the cover support bracket.
 

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This sounds pretty much like my problem except that the dash range indicators aren't working at all. I remember seeing alot of sticky old coke syrup in the rear cup holders-assuming this could indicate that the MICU took a sip and died. Im going to inspect and clean all this tomorrow. Thanks for another place to look-I was running out of ideas!
 

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So far it looks like I'm on the right track. Green fuzz around the MICU connector and same kind of corrossion around all the chip pins on the board. I doubt cleaning it up will bring it back to life. If only I could find one for less than $305...Scared of finding a damaged junkyard unit. Hmmm... :cry:
 
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