Here is what the shop manual says about P0122
, and P0155
. P0155 has the same possible causes as P0135
What they have in common is a low voltage condition, one a low Vref
(reference voltage) from the PCM. The other a low Vpwr
(system [battery] power) level. This could be a wiring problem, or just low battery output.
Check the battery terminals to make sure they are clean and solidly connected, also check the voltage at the battery posts (the posts, not the terminals). It should be 12.6 V with the battery fully charged and stabilized (5 to 10 minutes after shutting down the engine)--if it is not then the battery is not charging properly.
If the battery post voltage is OK then check the voltage between the battery terminals, it should be close to the battery voltage not more than 0.1 V less. If it is less than that check the connections.
Next check the voltage between the positive battery terminal and the engine block. It too should be within 0.1 V of the battery voltage--if not there is a bad ground connection between the battery negative (ground terminal) and the block.
Monitor the battery voltage while cranking the engine, it should not drop below 10.5 V--if it does the battery has a bad cell, you will need a new battery or the battery is not fully charged. You can find the complete charging system description and diagnostic tests by going to my website and making these menu selections:
- 2003 GT, UPR X, 24lb/h injectors, Magnaflow, 180° stat,
PP 70mm TB & plenum, Ralco RZ_flywheel, RAM HDX clutch, 3.73s, 262 rwHP/305 lb-ft.
new ride - 1998 SL500, 5.0L 32V 326/347 HP/tq