it is such a code of 4 numbers you have to enter when you try to program new key eather lost or espair
The diagnostic code 12 51 55 is actually not a code for the 1994 Jeep Grand Cherokee Laredo. The 12 means that it has started searching for codes. The 51 is oxygen sensor stuck lean. The 55 means it is finished searching for codes. Getting this means nothing is wrong.
That is a fan relay error. Recommend replacing the relay, these jeeps are notorious for burning them up.
1990 will require an OBD1 reader
how to fix or check po 206
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Trouble code P0720 means:Output speed sensor circuit malfunction
The diagnostic code 12 51 55 is actually not a code for the 1994 Jeep Grand Cherokee Laredo. The 12 means that it has started searching for codes. The 51 is oxygen sensor stuck lean. The 55 means it is finished searching for codes. Getting this means nothing is wrong.
P0725 indicates Engine Speed Input Circuit Malfunction.
The computer has detected a malfunction and set a trouble code.
The code can be cleared by unhooking the battery. The light will return if the failure is not repaired.
Trouble code P0155 means:O2 sensor heater circuit malfunction (Bank 2 Sensor 1)
P0123 TPS volts high. Replace the throttle position sensor.
With a scan tool.With a scan tool.
Trouble code P0320 means: Ignition/Distributor Engine Speed Input Circuit
Basically it means it means you have a invalid skim key and you are going to have to replace the i mobilizer module with new keys and reprogram.
According to Haynes, this represents a misfire in cylinder 6.
The only proper way is with a scan tool. Unhooking the battery might clear the code temporarily, but it will return if not fixed.