-
Notifications
You must be signed in to change notification settings - Fork 1
/
WHEN TO REPLACE YOUR PCM (AND WHEN NOT TO).htm
208 lines (161 loc) · 11.6 KB
/
WHEN TO REPLACE YOUR PCM (AND WHEN NOT TO).htm
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
<!-- saved from url=(0054)http://www.obdii.com/articles/When_To_Replace_PCM.html -->
<html><head><meta http-equiv="Content-Type" content="text/html; charset=windows-1252">
<title>WHEN TO REPLACE YOUR PCM (AND WHEN NOT TO)</title>
<meta http-equiv="DESCRIPTION" content="When to Replace Your PCM (and when not to) - An Article from the OBDII Technical Library">
<meta http-equiv="KEYWORDS" content="powertrain control module pcm replacement malfunction indicator lamp mil check engine fix diagnose diagnosis obdii obd-ii">
</head>
<body bgcolor="#FFFFFF">
<table width="575" border="0" align="center" cellpadding="4" cellspacing="0">
<tbody><tr>
<td><p align="right"><a href="http://www.obdii.com/obdii.html"><img src="./WHEN TO REPLACE YOUR PCM (AND WHEN NOT TO)_files/bluelogosm_at_top.GIF" alt="The OBD II Home Page - On-Board Diagnostic System Information" border="0" width="135" height="66"></a><br>
<a href="http://www.autotap.com/"><img src="./WHEN TO REPLACE YOUR PCM (AND WHEN NOT TO)_files/spsm_at.GIF" alt="Autotap® OBDII Diagnostic Scanner" border="0" width="135" height="45"></a></p>
<p align="center"><font size="3" face="Arial, Helvetica, sans-serif" color="#CC0000"><strong>WHEN TO REPLACE YOUR PCM<br>(AND WHEN NOT TO)</strong></font></p>
<font color="#000000" size="2" face="Arial, Helvetica, sans-serif">
<p>The onboard computer is the brains of the engine control system, so when the
brain isn't functioning correctly neither is the engine or anything else that
the microprocessor controls - which may include the charging system,
transmission, various emission controls and communications with other onboard
control modules. Once a diagnosis has been made (and I emphasize the word
diagnosis), then and only then should the PCM be replaced. </p>
<p>All too often, the blame falls on what is least understood. If an
engine isn’t running right and the cause isn’t obvious, blame the
computer. Throwing parts at a problem in an attempt to solve it may be good for
the parts business, but attempting to return a replacement PCM because it didn’t fix
the problem isn’t good for anyone. Warranty returns on complicated and
expensive components like powertrain control modules can be tricky and are a no-win situation for everyone. </p>
<h1><font size="3" face="Arial, Helvetica, sans-serif" color="#CC0000"><strong>UNNECESSARY RETURNS</strong></font></h1>
<p>Over 50 percent of PCMs that are returned under warranty
have nothing wrong with them! So it’s obvious a lot of people are swapping computers to see if a
different PCM will fix their problem.</p>
<p>The trouble with returns is if the PCM has been on the car, you have no way of
knowing if it is still "good" or not. Somebody may have crossed up some wires,
zapped the PCM with too much voltage or who knows what? The computer needs to be
tested and verified before it can go back on the shelf and be sold to somebody
else. </p>
<p>Unfortunately, there’s no easy way of doing that in a parts store. The PCM has
to be hooked up to a sophisticated simulator that exercises all of the
computer’s input and output circuits to make sure it works correctly - which
means the PCM has to go back to the supplier, be retested, and if no fault is
found, repackaged and put back into stock.
You can understand then why many parts stores have a policy of "no returns or
refunds on electronic components." </p>
<p>So - don't even think about replacing that PCM until you're confident that you've properly diagnosed the problem.</p>
<h1><font size="3" face="Arial, Helvetica, sans-serif" color="#CC0000"><strong>WHY DID IT DIE? </strong></font></h1>
<p>One way to reduce the risk of PCM warranty problems is to find out why the old
PCM died. Determining the cause of death may not always be possible, but it may
be essential to prevent the same thing from damaging the replacement PCM in some
cases. </p>
<p>PCMs typically fail for one of two reasons: voltage overloads (often due to a
short in a solenoid or actuator circuit) or environmental factors (corrosion,
thermal stress or vibration). If the shorted solenoid or actuator isn’t found
and repaired, the voltage overload it creates may damage the replacement PCM,
too.
</p>
<p>As for environmental factors, water is the main thing to avoid. If water gets
inside a PCM, it can short circuits and set up irreversible corrosion that ruins
electronic connections. Most remanufacturers won’t even attempt to repair a PCM
if the vehicle it came out of was submerged in a flood. Replacement is the only
option. Thermal stress and vibration can form microcracks in circuit boards
(which are repairable). This often has more to due with the ruggedness of the
circuit design than operation factors in the vehicle itself.</p>
<h1><font size="3" face="Arial, Helvetica, sans-serif" color="#CC0000"><strong>ACCURATE IDENTIFICATION</strong></font></h1>
<p>Because there are so many different PCMs, accurate identification of the PCM and
its correct replacement is absolutely essential to prevent unnecessary returns.
Many PCMs appear to be exactly the same on the outside (same sized box and
connectors) but may be wired or calibrated differently inside.
If the wrong PCM is installed in a vehicle, it may run but probably won’t run
well. Close enough isn’t good enough when it comes to replacing PCMs. It must be
the correct replacement for the application.</p>
<p>Accurately identifying the PCM requires not only the vehicle year, make, model
and engine size, but also the OEM part number on the PCM itself. Most supplier’s
catalogs list replacement PCMs both ways. So if in doubt, always refer to the
OEM number on the PCM and look it up in the suppliers cross reference index to
find their replacement part number.</p>
<p>The calibration chip and PROM contains the programming instructions for the
vehicle application. That’s why it usually doesn’t come with the replacement
PCM. There are too many different possibilities. On many newer vehicles, flash
memory or "EEPROMs" (Electronically Erasable Program Read Only Memory) are used.
If the replacement PROM is not properly programmed for the application, it must
be reprogrammed after it has been installed. </p>
<p>Unfortunately, the ability to do this type of reprogramming is not readily
available to the aftermarket. The car makers don’t want aftermarket technicians
messing around with the calibration of their onboard computers because they’re
afraid doing so may alter emissions or performance. But that’s another issue.
One such example is Chrysler transmission modules. They must be reset with the
factory DRB scan tool and dealer codes to set the "pinion factor," which
controls the operation of the speedometer. </p>
<h1><font size="3" face="Arial, Helvetica, sans-serif" color="#CC0000"><strong>REMAN PCMs</strong></font></h1>
<p>Because PCMs are fairly expensive, almost all aftermarket replacement PCMs are
"remanufactured" units. PCMs are not rebuilt in the same way that alternators
and water pumps because there are no mechanical parts that wear out.
Remanufacturing in this case usually means testing the computer, isolating and
repairing any faults that may be found, then retesting the computer to make sure
everything works correctly.</p>
<p>Remanufactured PCMs are typically sold one of two ways: on an exchange basis
from stock, or on a custom rebuild basis. If a particular PCM is not in stock or
is unavailable, you can often send the old PCM to a remanufacturer
for repair. Turn around time is typically a few days and the cost is the same as
selling him an exchange unit from stock (except there’s no core charge).
Some PCMs, though, may not be repairable. As we said earlier, most
remanufacturers will not even touch a PCM if it came out of a flooded vehicle.
</p>
<h1><font size="3" face="Arial, Helvetica, sans-serif" color="#CC0000"><strong>REPLACEMENT TIPS</strong></font></h1>
<p>Replacing a PCM is essentially a matter of swapping boxes. Accessibility can be
a problem on some vehicles because the PCM is often buried under or behind other
components in the instrument panel, climate control system or console. Some are
located under a seat and require removing the seat.</p>
<p>Regardless of the PCM’s location, though, one thing every installer should do
(but many don’t) prior to removing the old PCM and installing the replacement
PCM is disconnect the battery.</p>
<p>Once the PCM has been installed and reconnected, the battery can be reconnected,
too. But the job isn’t done yet. Many PCMs have to undergo a "relearning"
procedure after they’ve been installed or if they’ve been disconnected from the
battery.
</p>
<p>On some applications, there may be a specific procedure for establishing the
base idle speed. On others, it may be necessary to take the vehicle for a short
test drive so the computer can adjust itself. The exact requirements will be
spelled out in the vehicle’s service manual, but that doesn’t mean the installer
has access to a manual or will use it. So the best advice here is to test drive
the vehicle after the computer has been installed. A short drive cycle that
includes going over 35 mph will usually reset most computers so they run
properly.</p>
<p>Most PCMs will also continue to learn and make small adjustments to the fuel
mixture and other functions over time as the vehicle accumulates miles. If the
PCM also controls the transmission, it may take awhile to relearn the driver’s
habits so the transmission may not shift exactly the same as before until this
occurs.</p>
<p>Finally, if the Malfunction Indicator or Check Engine light comes back on after
the PCM has been replaced, it means there’s still a problem with the vehicle -
not the PCM (assuming the code is not one for an internal PCM fault, in which
case the PCM would be saying it is faulty). The presence of fault codes means
something else is wrong that needs to be diagnosed and repaired. So until the
real problem is found and fixed, the PCM may not function normally. </p>
<p>If the engine control system is not going into closed loop, chances are the
coolant sensor or oxygen sensor are not working properly. If spark timing seems
to be over advanced or retarded, the problem may be a faulty MAP sensor,
misadjusted throttle position sensor or overly sensitive knock sensor. And if
nothing seems to work right, low charging voltage due to a weak alternator or
poor battery connections may be the fault.</p>
<p>Remember, the PCM needs all its sensor inputs, proper battery voltage, a good
ground and the ability to send out control signals to function normally. </p>
</font></td></tr></tbody></table>
<p align="center"><font face="arial" size="2" color="black"><a href="http://www.obdii.com/articles/When_To_Replace_PCM.pdf">.pdf version</a></font></p>
<p align="center"><font face="arial" size="2" color="black"><a href="http://www.obdii.com/obdii_library.asp">Return to OBDII Library</a></font></p>
<p align="center"><font color="#000000" size="2" face="Arial, Helvetica, sans-serif">
© 2011 B&B Electronics<br>
</font></p>
<p align="left"></p>
<p align="left"></p>
<script type="text/javascript" async="" src="./WHEN TO REPLACE YOUR PCM (AND WHEN NOT TO)_files/ga.js"></script><script type="text/javascript">
var _gaq = _gaq || [];
_gaq.push(['_setAccount', 'UA-20693869-1']);
_gaq.push(['_setDomainName', '.obdii.com']);
_gaq.push(['_trackPageview']);
(function() {
var ga = document.createElement('script'); ga.type = 'text/javascript'; ga.async = true;
ga.src = ('https:' == document.location.protocol ? 'https://ssl' : 'http://www') + '.google-analytics.com/ga.js';
var s = document.getElementsByTagName('script')[0]; s.parentNode.insertBefore(ga, s);
})();
</script>
</body></html>