2002 Nissan Altima 2.5L mil lamp on

Car problem question:

Me and my neighbor is troubleshooting my 2002 Nissan Altima. The check engine light is on and we got P1574 code. It means ascd speed sensor ecu/icc signal different but we don't know what it means. We scanned it because the dash panel speedometer is going all over the place and the transmission is stuck in first gear which I understand as LIMPED MODE. However, when we hooked up the scan tool, everything works! What happen?

ATS Adviser:

Just looked at the computer data line diagram for this vehicle and this is what I see. Using the DLC pin terminals, Pin 3 and PIN 4 are ground terminals. You have to test that with a DVOM with your scanner disconnected. The reason your symptom was coming out with scanner connected because one of these 2 ground DLC terminals were open or not connected.

When you use the scanner, it connects to both of them restoring the grounds going to the vehicle modules. To test, get hold of a ground distribution wiring diagram and check all the ground circuits going to the module circuits especially the ECM. Check also the ground connection terminals for the bus modules located at the front of the engine and behind the right side of dash.

Shown below is a typical 2002 Nissan Altima Bus Module Wirings. Kline bus wire (pin 7) is 5-7 volts at key on engine off (KOEO). Both Can bus wires are + or - 2.5 volts at pin 3 and pin 6 terminals at DLC.

2002 Nissan Altima Bus Module Wires

For more details, you can get a complete wiring diagram for this vehicle from most parts store when you buy parts or get it free online when you join ATS.

FINAL FIX:

We found a loose ground connection for the ECM ground wire. We tighten it and everything is back to normal. We use the ECM and bus wiring diagram for locating the ground connections. Thanks for the TIP!

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