Always post the year/engine in your threads. By your public profile, I see that your XJ is a 97.
Read the TSB I've posted below for your P1398, it applies to your 97.
As for your 42 code, it has to do with your ASD relay. You could try swapping in a new relay to see if that helps; located inside the power distribution center under the hood. Here is a link to some more information on the 42.
http://autorepair.about.com/library/faqs/bl561g.htm
Using a code reader or scan tool and getting the full code (like P1398) is more helpful than the 2 digit codes that come up with key-on, key-off trick.
Good luck and let us know what you find!
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"NUMBER: 25-003-01
GROUP: Emissions
DATE: Feb. 23, 2001
This bulletin is supplied as technical information only and is not an authorization for repair. No part of this publication may be reproduced, stored in a retreival system,
or transmitted, in any form or by any means, electronic, mechanical, photocopying, or otherwise, without written permission of DaimlerChrysler Corporation.
SUBJECT:
Erroneous DTC P1398 (or $BA) - No Crank Sensor Learn
OVERVIEW:
This bulletin involves selectively erasing and reprogramming the Powertrain Control
Module (PCM) with new software (calibration level 96Cal18 or 97Cal18).
MODELS:
1996 - 1997 (AB)
Ram Van
1996 - 1997 (AN) Dakota
1996 - 1997 (BR/BE) Ram
Truck
1997 (TJ)
Wrangler
1996 - 1997 (XJ) Cherokee
1996 - 1997 (ZJ)
Grand Cherokee
NOTE: THIS BULLETIN APPLIES TO
VEHICLES EQUIPPED WITH
A GASOLINE ENGINE.
SYMPTOM/CONDITION:
A customer may experience a MIL (Check Engine Lamp) illumination due to an
erroneous DTC P1398 - No Crank Sensor Learn. This DTC may also be displayed as
a $BA - Adaptive Numerator at Limit. This condition may be caused by a momentary
drop in the supply voltage to the powertrain control module.
This condition may occur when a normal, or higher, electrical load is applied to the
battery. A momentary drop in the supply voltage to the PCM may be caused by a
marginal battery or poor electrical connections from the battery to the PCM. The
condition may be further aggravated by cold ambient temperatures or when the
vehicle has been left unused for an extended period of time.
DIAGNOSIS:
1. Verify the calibration level of the PCM software. If the PCM software is at 96Cal18 or
97Cal18, or higher, then this TSB does not apply. Further diagnosis is required.
2. If PCM software is earlier (lower or less) than either 96Cal18 or 97Cal18,
then perform the Repair Procedure.
PARTS REQUIRED:
Qty. Part No. Description
1 04669020 Label, Authorized Software Updade
1 04275086 Label, Authorized Modification
EQUIPMENT REQUIRED:
CH6000 Scan Tool (DRB III®)
CH7035 General Purpose Interface Bus Cable (GPIB)
CH7000/7001 J1962 Cable
MDS2 (Mopar Diagnostic System)
NOTE: THE MDS2 MUST BE OPERATING AT CIS CD 2077 OR HIGHER.
REPAIR PROCEDURE:
1. Reprogram the PCM using the MDS2 (Mopar Diagnostic System)
and the DRBIII® (Scan Tool).
NOTE: DUE TO THE PCM REPROGRAMMING PROCEDURE, A DTC MAY BE SET IN
OTHER MODULES (BCM, MIC, SKIM, ETC.) WITHIN THE VEHICLE, IF SO EQUIPPED.
SOME DTC’S MAY CAUSE THE MIL TO ILLUMINATE. ALL DTC’S RELATE TO A
LOSS OF COMMUNICATIONS BETWEEN MODULES. CHECK ALL MODULES,
RECORD THE FAULTS, AND ERASE THESE FAULTS PRIOR TO RETURNING THE
VEHICLE TO THE CUSTOMER. ERASE ANY FAULTS IN THE PCM LAST, AFTER
ALL OTHER MODULES HAVE HAD THEIR FAULTS ERASE.
NOTE: THE FOLLOWING STEPS ARE REQUIRED BY LAW.
2. Type the necessary information on the “Authorized Software Update Label”
p/n 04669020 (Fig. 1). Attach the label to the Powertrain Control Module
and cover the label with the clear plastic overlay.
Fig. 1 AUTHORIZED SOFTWARE UPDATE LABEL
3. Type the necessary information on the “Authorized Modification Label” p/n
04275086 and attach the label near the VECI label (Fig. 2). "
, then you can add your signature.
